Sailing boats' Stability, STIX and Old Ratios [Archive]

Guillermo

09-03-2006, 03:41 PM

Jeff promised, a long time ago, to open a Forum about Stability issues. Because he can always transfer this thread to such a Forum, if ever created, I post this thread to discuss Sailing boats' Stability, their STIX and the correlation with 'old' ratios and parameters.

To begin with, here the numbers for two cruisers, one light and more 'modern' and the other one more conservative. The numbers were taken from the article written by Rolf Eliasson, one of the fathers of the STIX number, in Professional Boat Builder magazine, February/March 2003. Let's call the boats RED and BLUE, as they appear in the article. I will consider only displacement as Mmsc (Some kind of medium load), as this is the one giving the lowest figure for STIX in both cases, which is the mandatory one to be asigned to the boat.

Let's see:

RED's BASIC DATA:
Overall Hull Length = 11,98 m
Length Waterline = 10,57 m
Flooded Buoyancy (Y/N) = N
Beam Waterline = 3,27 m
Beam = 4,1 m
Tc (HD) = 0,55 m
T = 2.38 m
Displacement MSC = 5165 kg
Displacement Max = 6190 kg
Ballast = 1300 kg (guess; does not influence any ratio or factor other than W/Disp)
Height of CE above DWL = 6,87 m
Height of CLR below DWL = 0,95 m
Angle of vanishing stability, Avs = 123 deg
Downflooding angle Afl = 137 deg
GZ at downflooding angle = -0,23 m
GZ at 90 degrees = 0,58 m
Sail Area = 71,1 sq.m
Area to flooding (Agz) = 74,46 m.deg (The one to be used in this case, as Afl >Avs)
Area to Avs = 75,6 m.deg

RED's 'OLD' RATIOS AND PARAMETERS
Length/Beam Ratio L/B = 2,75 -- being L = (Lod+Lwl)/2
Ballast/Disp Ratio W/Disp = 0,25
Displacement/Length Ratio D/L = 121,99
Sail Area/Disp. Ratio SA/D = 24,18
Power/ Disp. Ratio HP/D = 4,74 HP/ton
Hull speed HSPD = 7,89 Kn
Potential Maximum Speed PMS = 9,78 Kn
Velocity Ratio VR = 1,24
Capsize Safety Factor CSF = 2,39
Motion Comfort Ratio MCR = 15,2
Heft Ratio HF = 0,5
Angle of Vanishing Stability AVS = 116 º
Roll Period T = 1,93 Sec
Roll Acceleration Acc = 0,3 G's
Stability Index SI = 0,47
Upright Heeling Moment UHM = 19635,03 Ft*pound
Heeling Moment at 1º HM1º = 1306,88 Ft*pound
Dellenbaugh Angle DA = 15,02 º

RED's FACTORS AND STIX
Base Length Factor = 11,040
Displacement Length Factor (FDL) = 0,914
FL = 1,001
FB = 2,519
Beam Displacement Factor (FBD) = 0,815
FR = 3,066
Knockdown Recovery Factor (FKR) = 1,146
Inversion Recovery Factor (FIR) = 1,010
Dynamic Stability Factor (FDS) = 1,361
Vaw = 1,000
Wind Moment Factor (FWM) = 1,000
Downflooding Factor (FDF) = 1,522
Delta = 0
STIX = 42,546

ASIGNED DESIGN CATEGORY: A
Wave height max 7 metres (significative)
Windspeed max. Force 10

BLUE's BASIC DATA
Overall Hull Length = 12,2 m
Length Waterline = 10,52 m
Flooded Buoyancy (Y/N) = N
Beam Waterline = 3,2 m
Beam = 3,65 m
Tc (HD) = 0,80 m
T = 2,00 m
Ballast = 3600 kg (guess; does not influence any ratio or factor other than W/Disp)
Displacement MSC = 10319 kg
Displacement Max = 11769 kg
Height of CE above DWL = 6,65 m
Height of CLR below DWL = 0,8 m
Angle of vanishing stability Avs = 147 deg
Downflooding angle Afl = 114 deg
GZ at downflooding angle = 0,4 m
GZ at 90 degrees = 0,67 m
Sail Area = 72,5 sq.m
Area to flooding (Agz) = 57,42 m.deg
Area to Avs = 66,83 m.deg (The one to be used in this case, as Avs>Afl)

BLUE's 'OLD' RATIOS AND PARAMETERS.
Length/Beam Ratio L/B = 3,11 -- being L = (Lod+Lwl)/2
Ballast/Disp Ratio W/Disp = 0,35
Displacement/Length Ratio D/L = 247,21
Sail Area/Disp. Ratio SA/D = 15,54
Power/ Disp. Ratio HP/D = 2,37 HP/ton
Hull speed HSPD = 7,87 Kn
Potential Maximum Speed PMS = 8,26 Kn
Velocity Ratio VR = 1,05
Capsize Safety Factor CSF = 1,69
Motion Comfort Ratio MCR = 35,35
Heft Ratio HF = 1,24
Angle of Vanishing Stability AVS = 123 º
Roll Period T = 3,66 Sec
Roll Acceleration Acc = 0,07 G's
Stability Index SI = 1
Upright Heeling Moment UHM = 19074,33 Ft*pound
Heeling Moment at 1º HM1º = 697,53 Ft*pound
Dellenbaugh Angle DA = 27,35 º

BLUE's FACTORS AND STIX
Delta = 0
Base Length Factor = 11,080
Displacement Length Factor (FDL) = 1,033
FL = 1,001
FB = 1,781
Beam Displacement Factor (FBD) = 1,047
FR = 7,170
Knockdown Recovery Factor (FKR) = 1,508
Inversion Recovery Factor (FIR) = 1,240
Dynamic Stability Factor (FDS) = 1,040
Vaw = 1,000
Wind Moment Factor (FWM) = 1,000
Downflooding Factor (FDF) = 1,267
STIX = 52,100

ASIGNED DESIGN CATEGORY: A
Wave height max 7 metres (significative)
Windspeed max. Force 10

Well, thinking CE marking is not conceived for racing boats, but for the recreational market, where most of cruising boats are short handed and boats should look after their crews, in my humble opinion, I think it's worrying that the RED boat can be labelled as Category A, taking into consideration it has what has been commonly understood for many years, among designers, NA’s and boat owners, as 'cruel' and even dangerous ratios and parameters. The boat is too stiff by all means, with a low motion comfort ratio, too high accelerations (And so quite punishing for a short handed crew) and with a Capsize Safety Factor well above 2, widespread considered a safe limit.
BLUE boat seems to be much better suited for ocean crossings than RED, both from the point of view of 'old' ratios and the STIX.

As we can see STIX provides not enough information about the seaworthiness of a boat (It was never intended to be a clue to this, but this idea is spreading around quickly) and may even be a tricky and dangerous number. Seaworthiness is a complex matter, involving stability, all around scantlings, quality of movements, and a long etc.

I think manufacturers/designers should at least be obliged to publicize the STIX Factors and not only the number itself (Which is not even mandatory!). And even better, publish also the 'old' ratios and parameters, for the people to have a more complete view and understanding of the boat.

Rolf Eliasson himself expressed some serious concerns about the STIX number and how it finally 'came to life', in the aforementioned article. He even suggested minimum STIX for Categories A and B should be 40 and 28, instead of 32 and 23 as it is now. But even rising the level provides not enough guarantee as to define a boat as seaworthy, as we could see per numbers above.

Again in my opinion, most probably a great pressure from modern mass (and light) boats producers (and their designers) was put into the process. Those manufacturers produce very nice boats for Club racing and coastal cruising in fair weather (what most of users do) and fun to sail, but of course they want not many of their models to be obliged to be labelled as Category C, what they should be in most cases.

Long range racing is quite a different thing (with full trained crews aboard), than family oceans crossings so, in my opinion, CE Category's assigning criteria should be revised and adequate to the RCD’s own reason of existing. If racing is intended, a new special Category or Note should apply in addition to the ‘familiy’ Category.

I recommend the reading of Rolf Eliasson's article. Here a LINK (http://www.woodenboatstore.com/products.asp?dept=7&pagenumber=11&sort_on=&sort_by=) to buy the magazine issue. Search for number 81. Also here a LINK (http://www.rina.org.uk/rfiles/HISWA/1994/Investigation%20of%20minimum%20stability%20requirements%20for.pdf) to a very interesting document written before 1996 by Dr. Peter van Oossanen, another STIX father.

I attach again SailDesign's STIX spreadsheet, with a further correction to allow for downflooding angles greater than AVS.

Now, your comments.

Guillermo

09-04-2006, 06:36 PM

A last correction (And I hope the very last one!) of the STIX spreadsheet.

Guillermo

09-08-2006, 01:42 AM

Interesting....
No comments at all? :(

M&M Ovenden

09-08-2006, 08:47 AM

Guillermo,

I'll jump in for a comment. I find all the stability discussion very interesting and have enjoyed reading most of your postings on the subject. It can be sometimes a little uncomfortable to post comments and questions as we feel we are dealing we some big boys of boat design.
So about the STIX. I find the index really interesting and quite well thought threw even though it doesn't, as you point out, on its own mean enough to decide of the seaworthiness of a boat. I don't think the problem is the index itself but more that tendency of our modern societies to want everything simplified into standards. The standards themselves are not the problem but more the habit of many to blindly rely on them. Standardization tends to deresponsibilize individuals by making them feel safe without anymore questioning. On an issue as boat stability there are way to many variables to bring it down to a simple binary answer. But most people want simple answers, they don't want to understand why a boat is considered stable and safe.
This is unfortunate because there is no perfect boat and understanding the specific characteristics of a vessel will lead to different ways to face weather and make the boat safer by taking advantage of its own abilities.
So the problem with any index is the blind confidence most people put into it as soon as some authority starts using it. Coming up with a different index for cruising boats wouldn't make much difference, a ballasted log would probably qualify. Understanding of each specification and good common sens is the best index and I agree they should be published.

Heres a question about a variable used for STIX. What is considered for down flooding angle?
Does it stop at watertight opening portholes, or the same porthole if they have deadlights, or at any possible opening? Or is it left to the designers judgment? I couldn't find a clear answer.

Cheers
Murielle

Tim B

09-08-2006, 09:23 AM

STIX is intended to allow classification, it is an indication of a yacht's stability, not a Quick-Fix answer. Thinking that STIX will give a be-all-and-end-all answer is foolish. No single number can sum up any boat. They are too complex for that.

Taken to it's greatest extreme it could be argued that the RAOs and full stability data are made public. How many sailors fully understand RAOs or would be able to use them. Similarly, how many would back off well before GZmax. There are people on this forum who don't like 20 degrees of heel, let alone 70!!!

What information is divulged is largely down to the designer. And generally they get it about right.

Tim B.

PS. Will explain Downflooding later when I've had chance to look at ISO again.

Vega

09-08-2006, 11:37 AM

Guillermo

09-08-2006, 06:15 PM

Sensible post, Murielle.
Downflooding angle for this kind of boats is the one at wich water may enter the boat trough a non watertight opening under ISO rules. So watertight portholes or hatches under the ISO rules, even if may be left opened, shall not be considered in the calculations, but the "lowest" opening not being watertight under them. Usually one of the the top corners of the companionway is the considered downflooding point as this companionway uses not to be watertignt (This is the "lowest" point as top corners are upside down when heeled in sailing boats having a downflooding angle greater than 90º).

Relevant information on watertightness shal be looked at in EN ISO 12216:2002 "Small craft - Windows, portlights, hatches, deadlights and doors - Strength and watertightness requirements" and EN ISO 11812: 2001 "Small craft - Watertight cockpits and quick-draining cockpits"

Guillermo

09-08-2006, 06:41 PM

STIX is intended to allow classification, it is an indication of a yacht's stability, not a Quick-Fix answer.......How many sailors fully understand RAOs or would be able to use them.....
Precisely! The problem is that as people understand almost nothing about these matters, they tend to fix to a simple rule, as it couldn't be other way. And STIX is becoming dangerously a kind of 'magic' number among boatowners. What is worst, this Design Categories scheme is tending to confuse people's judgement on a boat's ability to survive bad weather, in my opinion. I think nowadays Category A means in a growing number of people minds, that the boat is able to go anywere, which is not true even under the RCD. Categories are a clue but not a 'Safety Act'. In my opinion this misunderstanding is being consistently encouraged by manufactures; and designers as well....:(

Taken from the "Recreational Craft Directive and Comments to the Directive Combined":
"The directive does not include any navigation or usage rules and there is no link between the design categories and any such rules; taking into account construction safety, the user is only clearly informed of what the boat was designed and built for in relation to certain parameters of significant wave heights and wind speeds."

Guillermo

09-08-2006, 08:06 PM

In my opinion you mistake comfort with safety....
In my opinion I don't. :)
Comfort is just one of the factors in safety, specially important with short handed crews.

I agree that the Blue is a much more comfortable boat than the Red, but may I point out to you that the Red has a downflooding angle of 137º with an AVS of 123º and that the Blue has an AVS of 147º but a somewhat poor downflooding angle of only 114º.
Downflooding point has been taken as being one of the the top corners of the companionway for both cases. As you point out, the BLUE boat has a much better AVS than the RED, but flooding angle is lower as the RED is beamier and lighter. This only gives the RED an advantage in the Dynamic Stability Factor (FDS) as FWM and FDF are the same (*) as well as length correction (FL), which is not actually a factor in itself but a part of the FDL factor. BLUE boat is better in all other respects except the Dynamic Stability Factor (FDS), where RED has an advantage. The reason for this is that in all remaining factors (FIR, FKR, FDL and FBD) the displacement plays an important part, and the Blue boat is the heavier of the two.

The FDS is calculated using the positive area under the righting arm curve, up to the Avs in this case (as Afl>Avs). So the entire positive area under the curve is used, which is big thanks to the wide beam. The usable positive area for the BLUE boat is limited to the downflooding angle (Afl) and this, joined to the narrower beam, gives much less area, so penalizing FDS.

But it has to be noted that, since STIX gives no consideration to the importance of the negative areas, it is fully possible to draw a boat that's wide and flat with a low center of gravity, with a GZ curve that reaches to the sky quickly, and then drops again as quickly as it rised, just passing the minimum Avs requirement, and producing a negative area almost as big as the positive one. Such a boat could still receive a category A rating, which it clearly does not merit; it would be unsafe in the conditions outlined in that category. (Rolf Eliasson)

As you know, for the calculation of the STIX number there are some factors that take into account the boat dimensions but there are others that are taken from real trials with the boat (RM and AVS)
Not exactly. RM curve is not considered to calculate STIX, but GZ curve. And this curve as well as the Avs value (as usually published at the magazines and quoted as being data provided by designers or manufactures), use to be get by calculation methods on estimated COG position, and not after an stability test, as it should be.

.... I am quite sure that 99% of the buyers will not have a clue about all those numbers.
I agree 100% . But market should be educated. It's designers, NA's, manufacturers and authorities' responsibility.

I disagree with you in what concerns the importance of the capsize screening formula.
As you know that formula does not take into account the vertical position of the CG and because obviously the Red has a Bulb in the end of a very deep Keel (draft is missing on the boat’s data) the CG of the boat will be lower than expected and if that was taken into account the Real Capsize Safety Factor would be a lot better.
Draft is not missing. You can find it as "T" for total draught and "Tc" for body draught.
And yes, RED is bulbed.
About the safety of the boat and CSF: Although symplistic, CSF gives a clue, and RED's value is quite high. And what this high value of CSF highlights, is supported in this case by the RED's much bigger negative area under the GZ curve than BLUE's (curves available at Rolf Eliasson's article), being BLUE inherently more safe than RED because of that.
On the COG's position, the RED boat, even having a bulb, has it located 5 cm above the waterline, while BLUE's is 2,5 cm under it.
As you can see, CSF seems to be quite right in this case.
(Interesting to note also that neither draught nor ballast are used, as direct input data, to calculate 'old' ratios or the STIX).

As you know there is a big discussion about what is acceptable as an AVS for an oceangoing boat. The actual norm is a minimum of 120º. I think that it should be at least 125º and personally I would not have a boat with less than 130º.
In my opinion Avs has become also one of those 'fixing factors' intended for widespread and easy understanding among not specialized people. Being important, of course, and generally speaking the higher the better, it should be used not alone but in conjunction with GZ at 90º value. A high value here is to ensure that the boat is able to right herself from a knockdown to an angle of around 90º. This is accomplished in the STIX calculation by means of the FKR factor, which (surprise!), is bigger for the BLUE boat.
Also GM at 180º or GZ max in the inverted position should be considered to have a better clue about the boat's ability to recover from a knockdown.

I believe you put too much of your personal preferences when analyzing a boat.
Yes. :)

....If you know little about boats and buy a boat that is government certified to go Offshore , it is normal that you think that it is safe to do so.:mad:
I again agree 100%

Quoting Rolf Eliasson again:
"...It's always possible to add more factors (To the STIX) without disturbing the end result, which should hover around a factor of 1. I'm thinking of Stability Loss due to Speed Factor, Transverse Inertia Factor, and GZ-area Ratio Factor (positive vs. negative areas), among others...."
1000% agree!!

(*) Please note, there is a mistake in FDF factor for both boats, as it cannot be greater than 1,25. I've already corrected the spreadsheet R3 constant in my second post)

Crag Cay

09-09-2006, 05:17 AM

Whilst it may be possible to argue that one boat is better than another for offshore work, the RCD (as a trade agreement - and nothing else), is there to ensure that 'patently unsafe' boats don't come to market.

It is a 'trading standards' regulation, in the same way as kitchen appliances get a CE mark: It guarantees that an electric toaster, for example, with a CE mark shouldn't kill you in normal use, but it doesn't give you one iota of information about whether it makes good toast.

It's exactly the same with boats. Wind and waves of a stated size shouldn't kill you when a boat with that rated category is operated properly. It unfortunately does not indicated a good boat that Guillermo would enjoy sailing.

The laudable ambitions to harmonise trade within Europe by eliminating individual counties' specific boat design requirements, were under intense corrupting influences from the word go. Countries with boat use restrictions or licensing saw the RCD as an extension of those, marketeers saw the potential of 'high categorisation' of their products as a sales tool, and to be honest, a lot of designers and naval architects saw the rule, at worst, as an interesting intellectual exercise, and at best, an decent revenue stream by being a Notified Body.

Many of the current problems with the public's perception of the meaning of the RCD are only natural and predictable. A few of us warned that this would be the case, but our practical objections to the way it would be perceived and used in the real world were often confused with those who just objected to the whole thing on principal. At RINA conferences 10 or 12 years ago those who could see the selfish advantages in it had already got momentum. There was even completely fuzzy thinking by those who were involved in its conception. The top dog in the British marine industry's trade body kept going on about it being as 'significant as the introduction of the Plimsoll Line was to shipping', despite that being a 'restriction on use and practice', something the RCD was never intended to be, but might still become by de facto practice.

So any criticism of the RCD can only be made on the grounds that it is allowing boats that are patently dangerous to come onto the market. Not just indifferent, or undesirable or uncomfortable or misguided, but just down right lethal.

However, the (mis)use of RCD Categories as a marketing tool brings them under other legislation, namely the trade description regulations. Now a seller can only make claims for something that is truely 'fit for purpose'. This is open to a much broader interpretation and the courts in these case only have to decide whether you were miss-sold a product. If a boat proves in service to be unsatisfactory in any way for a purpose that the salesman and advertising had you believe otherwise, then you are entitled to redress. It's in this circumstance that the difference between the very restricted scope of the RCD and the much fuller implication of it given by the marketeers, would be revealed.

Guillermo

09-09-2006, 05:17 AM

Please everybody note:
Correcting FDF factor to its maximum of 1,25 for both boats, STIX numbers became 38,838 for RED and 51,756 for BLUE.
Sorry.

Excellent post, Crag Cay.

Vega

09-09-2006, 08:20 AM

Yes, I agree but I have some doubts about this:

So any criticism of the RCD can only be made on the grounds that it is allowing boats that are patently dangerous to come onto the market. Not just indifferent, or undesirable or uncomfortable or misguided, but just down right lethal.

However, the (mis)use of RCD Categories as a marketing tool brings them under other legislation, namely the trade description regulations. Now a seller can only make claims for something that is truely 'fit for purpose'. This is open to a much broader interpretation and the courts in these case only have to decide whether you were miss-sold a product. .

When a seller sells a 29ft boat with three tons, advertising that it is a certified Class A boat he is not saying that in his opinion it is an oceangoing boat, he is saying that the boat has passed the official independent RCD tests that certify the boat as capable to withstand “Wave height max 7 metres (significative) Windspeed max. Force 10”.

So, if this is not true and proves to be grossly and tragically misleading, it is not the seller that should be object of lawsuit, but the RCD. In my opinion it is not the seller that is miss-selling a product, but the RCA that is miss-certifying a product.

Seafra

09-09-2006, 09:07 AM

Are the "old" design parameters considered with the same weight and significance as the newer STIX factors?

How is GZ calculated at various angles?

Crag Cay

09-09-2006, 09:27 AM

I'm not claiming the RCD is beyond reproach. In fact ABS got out of plans appraisal and the small boat market just about the same time the EU was keen to jump in. It entirely possible that the requirements of each of the Categories will have to be revised if they prove to be inadequate.

My caution was to distinguish however, between the true aims of the Directive and the way compliance is used and projected by parts of the boat building industry. I still believe there is a greater danger of people being mis-sold a boat that proves unsuitable for them, than there is to find their dissatisfaction was due to a fundamental flaw in the RCD.

Seafra

09-09-2006, 09:43 AM

The flaw comes from people designing a boat to meet an isolated design spec without regard to the larger picture of true stability.

People buy spec sheets. And not detailed spec sheets, rather select few numbers with exagerrated importance to be "understood" by the simple and the lazy.

Vega

09-09-2006, 10:11 AM

I will post the STIX Formula and the Stix factors.

Guillermo says that the “ GZ curve… as well as the Avs value (as usually published at the magazines and quoted as being data provided by designers or manufactures), use to be get by calculation methods on estimated COG position, and not after an stability test, as it should be”.

But that information contradicts what I have been told (and read) and that is that the GZ curve is obtained with data taken from inclination trials on the prototype, conducted by an independent and certified body (Naval Architects cabinet). Those data are integrated with measures taken on the prototype and with computer simulations. They are not data provided by the manufacturer or by the boat designer.

The precise way to find the GZ curve and all factors in STIX are described in the ISO 12217-2, but it is an expensive document and I can not find it in the NET.

Guillermo, do you have it? Somebody does?

Guillermo

09-09-2006, 11:48 AM

The only way of getting a trustable GZ curve is having an accurate body forms plan, layout plans showing all tanks (even tanks plans, if necessary) and knowing COG position by means of a carefully performed inclining experiment.

I have ISO 12217, but at the office, not here at home. Yes, it can be downloaded from the net, but it has a price.

Notified Bodies are not persons, but companies, many of them also being Classification Societies. Among the many NBs I have reference of, I do not know any NA's gabinet, although probably several exist out there. Boats testing and assessment can be performed by people hired by those companies, being not necessarily NA's. They may even have not studies at all, just know how to do the thing.

GZ or RM curves published at magazines are provided by designers, NAs or manufacturers (Many of them state there so) and not by the Notified Body. The Notified body does not provide anything but the certificate after a satisfactory assessment. Necessary calculations are performed by an NA or designer and submitted for approval.

Vega

09-09-2006, 12:47 PM

RED's FACTORS AND STIX

FL = 1,001
FB = 2,519
FR = 3,066
Vaw = 1,000

Guilhermo, those are not STIX factors and don’t enter in the STIX formula. What is their meaning?

… This only gives the RED an advantage in the Dynamic Stability Factor (FDS) as FWM and FDF are the same … as well as length correction (FL), …. BLUE boat is better in all other respects except the Dynamic Stability Factor (FDS), where RED has an advantage.

Humm, the FDF (downflooding factor) is also substantially better on the Red boat.

The FDS is calculated using the positive area under the righting arm curve, up to the Avs in this case (as Afl>Avs). So the entire positive area under the curve is used, which is big thanks to the wide beam. The usable positive area for the BLUE boat is limited to the downflooding angle (Afl) and this, joined to the narrower beam, gives much less area, so penalizing FDS.

Don’t see anything wrong in it. The penalization seems right to me.

But it has to be noted that, since STIX gives no consideration to the importance of the negative areas, it is fully possible to draw a boat that's wide and flat with a low center of gravity, with a GZ curve that reaches to the sky quickly, and then drops again as quickly as it rised, just passing the minimum Avs requirement, and producing a negative area almost as big as the positive one. Such a boat could still receive a category A rating, which it clearly does not merit; it would be unsafe in the conditions outlined in that category.

I don’t fully agree, I mean, if the boat is big enough, eventually it could be Certified as Class A boat, but its STIX would be very low compared to its length and that would indicate a very poor boat in what concerns safety. Guillermo, I don’t see how the FIR (inversion recovery factor) can be calculated without taking into account the AVS and the inverted stability.

A clarification for the ones less familiarized with the STIX number. That indicator was conceived to give not knowledgeable people a fast and reliably information about the safety and stability of the boat. So that number was calculated to follow the length of the boat in feet. With a higher STIX than the length of the boat, you have a better boat (regarding safety); a lower number than the length means a not so good boat.

In my opinion Avs has become also one of those 'fixing factors' intended for widespread and easy understanding among not specialized people. Being important, of course, and generally speaking the higher the better, it should be used not alone but in conjunction with GZ at 90º value. A high value here is to ensure that the boat is able to right herself from a knockdown to an angle of around 90º. This is accomplished in the STIX calculation by means of the FKR factor, which (surprise!), is bigger for the BLUE boat.
Also GM at 180º or GZ max in the inverted position should be considered to have a better clue about the boat's ability to recover from a knockdown.

No, Guillermo, you are not reading well your numbers, the Red FKR (knockdown factor) is 1.146 and the Blue is 1.508. They are a lot bigger for the Blue. The FKR as you said, is the factor that takes into account the recovery from a Knock down (90º) and the other factor that takes into account the capacity from recovering from an inverted position, the FIR (inversion recovery factor) is also bigger in the Blue boat (1.010 to 1.240). So it seems that the correction factors of the STIX are doing their job.

Guillermo I have been following STIX numbers for a long time and I believe that they work well as a generic information about the boat’s safety (better than anything that was done till now) and I believe that they should be mandatory in every sailboat catalogue.

I agree with you that the complementary information about the force that the boat is making to right itself after a knock down, the total force needed to capsize the boat, the AVS and the total force needed to bring it back from an inverted position, is an important one. Those are important figures to understand the boat, but you don’t get any real conclusions with GZ numbers or curves (the ones that normally are published) but only with RM curves, the ones that are made from the GZ, but that doesn’t give you abstract values (in meters/Ton) but the real forces for that boat, taking in consideration the displacement and length of the boat you are looking at. The RM curve is the only that can give you the real forces that the boat can make to recover from a knock down or the force to resist an inversion.

Vega

09-09-2006, 01:40 PM

The only way of getting a trustable GZ curve is having an accurate body forms plan, layout plans showing all tanks (even tanks plans, if necessary) and knowing COG position by means of a carefully performed inclining experiment.

You mean that inclining experience is not made with a real prototype, but only in the paper and in the computer?

Notified Bodies are not persons, but companies, many of them also being Classification Societies. Among the many NBs I have reference of, I do not know any NA's gabinet, although probably several exist out there. Boats testing and assessment can be performed by people hired by those companies, who are not necessarily NA's.

Are you kidding me? I was talking about Naval Architect cabinet, meaning offices with Naval Architects (poor English). I see in internet lots of advertisements from that kind of offices for doing the Certification of boats.

The Notified body does not provide anything but the certificate after a satisfactory assessment. Necessary calculations are performed by an NA or designer and submitted for approval.

Do you mean that it is only a paper thing? You talk like if it was only a project approval, not a prototype approval. They don’t perform inclining experiences with the boat to see if the paper work matches with the reality?

About the GZ curves, obviously the Notified bodies don’t give them to magazines, but I have been several times waiting for GZ curves of new boats and the manufacturers refuse to provide them (I mean the ones from the project) till the prototype is made and subjected to tests, the ones that provide the certification. Obviously they don’t want any discrepancy between the projected curves and the real ones.

What I was meaning is that these curves are what the manufacturers provide to the magazines and not the ones from the project.

Seafra

09-09-2006, 04:37 PM

Guillermo

09-09-2006, 07:06 PM

Guilhermo, those are not STIX factors and don’t enter in the STIX formula.
They enter the STIX formula as part of STIX factors. Study the formulae.

Humm, the FDF (downflooding factor) is also substantially better on the Red boat.
FDF is 1,25 for both boats. Read post number 11

Guillermo, I don’t see how the FIR (inversion recovery factor) can be calculated without taking into account the AVS and the inverted stability.
Please, it would be useful for the sake of discussion if you learn first how STIX factors are calculated (I've posted an STIX spreadsheet calculator, so you can follow things there). Avs and Mmsc are the only input data for this factor. GZ curve's negative zone (What you call inverted stability), is not taken into account.

...So that number was calculated to follow the length of the boat in feet...
I would like to know on what numbers your statement is supported. Do you have any examples we can follow through the influence of the several STIX factors?

No, Guillermo, you are not reading well your numbers, the Red FKR (knockdown factor) is 1.146 and the Blue is 1.508. They are a lot bigger for the Blue. The FKR as you said, is the factor that takes into account the recovery from a Knock down (90º) and the other factor that takes into account the capacity from recovering from an inverted position, the FIR (inversion recovery factor) is also bigger in the Blue boat (1.010 to 1.240).
No, you're the one who's not reading well. Please don't try to mixtify what I wrote. Read it again carefully.

...but you don’t get any real conclusions with GZ numbers or curves (the ones that normally are published) but only with RM curves...
Don't make me laugh. You should tell this to all NA's, national authorities, IMO, Classification Societies, etc., etc., in the world, who assess stability using the GZ curves, instead of RM. Probably we are all stupid and do not know about our work. Please teach us. :rolleyes:

Vega

09-10-2006, 08:23 AM

If I'm understanding correctly, a boat with narrow beam will nearly always perform worse in terms of downflooding, and yet, a finer hull typically has less inverted stability and greater dynamic stability.

But if it's at the expense of downflooding...but really, how hard is it to make a companionway watertight?

Yes I guess you can say that about dynamic stability even if I would change your "near always" by normally. About the downflooding I would say that it is more difficult to make a generalization. A narrow beam boat does not have necessarily a worst downflooding angle than a beamier boat.

About the companionway, I would say that it is more important to have it closed when the boat capsizes. In many cases it is open and the severe downflooding that it origins is really dangerous and can prevent the boat to return to its normal position.

I will post two images that explain the differences in dynamic stability and in the RM curves between beamy boats relying more on form stability and narrow boats, reeling more on Ballast.

Vega

09-10-2006, 10:23 AM

Not exactly. RM curve is not considered to calculate STIX, but GZ curve.

From the paper :”RORC Safety and Stability Indices (SSI) SSSN and ISO 12217 Part 2, STIX”Developed in Co-operation with The RYA.

“In developing the new ISO 12217-2, Small craft, Stability and buoyancy assessment and
categorisation, Part 2, Sailing boats of hull length greater than 6 metres, the ISO working group has developed a stability index for assessing the stability and safety of sailing monohulls, known as STIX.
STIX is a development of SSS, but uses more detailed stability data, including some from a righting moment curve.

No, you're the one who's not reading well. Please don't try to mixtify what I wrote.

Yes, you are right, and I apologise, my mistake… but I don’t understand why you say that I try to mistify what you wrote. You have said:

A high value here is to ensure that the boat is able to right herself from a knockdown to an angle of around 90º. This is accomplished in the STIX calculation by means of the FKR factor, which (surprise!), is bigger for the BLUE boat. .

I guess that as you seem to have a somewhat low opinion about the utility of the STIX number, I have wrongly assumed that the sarcastic expression was related with the attribution, by the STIX rules to calculate FKR ,of a worst number to the boat that normally should have the best recovery factor from a knock down. well, as I have said I am sorry, but I have to say that this way I don’t understand your Sarcasm, nor why you are talking about “mystifying”. That doesn’t seem to make any sense to me, I did not have any intention of doing any wrongdoing.

FDF is 1,25 for both boats. Read post number 11.

I didn’t notice the post nº 11, but let me see if I got it right:

You Begin this thread Quoting an example referring a published article comparing two boats and saying : “The numbers were taken from the article written by Rolf Eliasson, one of the fathers of the STIX number, in Professional Boat Builder magazine, February/March 2003. “
Then you alter the numbers that you say that have been published assuming that Rolf Eliason has made a mistake in the calculation of the STIX numbers that he has published in that Article, and with a help of a spreadsheet that has been repeatedly modified, corrected the StIX numbers of both boats.

Sorry Guillermo, but that doesn’t seem right to me.

By the way, the calculated FDF can be bigger than 1.25, and that number you get is the correct calculated FDF for the boat. For calculation of the STIX number, if the FDF is superior than 1.25, it is this number that should enter in the calculations. Both numbers appear on the files that are presented for the boat certification, at least in the ones I have.

Don't make me laugh. You should tell this to all NA's, national authorities, IMO, Classification Societies, etc., etc., in the world, who assess stability using the GZ curves, instead of RM. Probably we are all stupid and do not know about our work. Please teach us. :rolleyes:

Here you are very disagreeable, to say the least. I don’t have the pretension to teach nobody, I am here to learn, but it seems that you have already learned everything.

I have explained why you should use a RM curve to understand the real stability of the boat (comparing it with others) instead of a GZ curve (and you didn’t explain why we should use a GZ).

A GZ curve is the tool to see if a boat is well designed or not, and it is that the reason that makes it a priority tool in the design of a boat. But for the buyer and to compare different boats regarding stability, it is the RM curve that matters. I have already explained why in a previous post.

Perhaps you care to read it again, or if you prefer it, I can put it in the words of Leif Angermark Marin, an Architect of international prestige and the designer (among others) of the Malo Yachts, that are reputed by his seaworthiness and concern with safety stability:

I will post also the GZ and RM curves of the boats he is talking about.
To sea the boats click on the link that I will post.

Obviously the GZ curves are the ones that look very similar. The RM curves are the ones that look very different, as different as the big real differences in stability between the boats to which they refer.

"G – Z curve versus real stability.

When we talk to "ordinary" yachtsmen, we frequently notice that it is very easy to misunderstand the meaning of the usually published stability curve that indicates the righting lever ( G-Z ). This curve alone is no measure of a yacht’s real stability.

To illustrate this statement we have prepared stability data for three different boats, and it is very common that the G-Z curves are interpreted as indicating that all 3 yachts have roughly the same capacity to resist a capsize.

In fact it is the curve of righting moment that illustrates this capacity.

Every wave contains a certain amount of energy en every vessel requires a certain amount of energy to be turned over. The energy required to capsize a ship is represented by the area of curve above the baseline, and energy needed to return it to an upright position is represented by the area below the baseline. NOTE: This is only valid for the curve representing the righting moment, NOT the G-Z curve.

Thus we can see that it takes more than 4 times more energy to overturn the MALÖ 43 as the 33 footer.

… A much better assessment of the real stability is thus to compare the curves of righting moment, and also look to the STIX number as defined in the ISO standard".

http://www.maloyachts.se/Portals/0/STABILIT.PDF

Seafra

09-10-2006, 01:41 PM

Vega,

Thanks for clarifying. I will agree that I overgeneralized in my previous statement. Those illustrations helped me to really understand the concept.

This may again be too far of a generalization but would you suppose that a finer hull will require more ballast than a beamier variant due it's diminished positive rm curve to be seaworthy and comfortable?

Guillermo

09-10-2006, 02:16 PM

You mean that inclining experience is not made with a real prototype, but only in the paper and in the computer?
Inclining experiment is always done on the real thing, but Annex C of the standard does allow the option of using calculated values.

Are you kidding me? I was talking about Naval Architect cabinet, meaning offices with Naval Architects (poor English). I see in internet lots of advertisements from that kind of offices for doing the Certification of boats.
Of course I'm not kidding you. It's not mandatory an NA tests and assesses boats under RCD. Not even to design them.

Do you mean that it is only a paper thing? You talk like if it was only a project approval, not a prototype approval. They don’t perform inclining experiences with the boat to see if the paper work matches with the reality? Yeap. Many times.

Vega

09-10-2006, 02:58 PM

Thanks for the clarification.

Dam bureaucrats::mad:

Guillermo

09-10-2006, 03:21 PM

“
STIX is a development of SSS, but uses more detailed stability data, including some from a righting moment curve.
Excuse me, but that's incorrect. Probably a typo or the like. RM curve IS NOT used, but the GZ curve. Just have a look at STIX input data.

About the GZ and RM issue, I'm not sure if you fully understand stability issues. Righting moment is only GZ * Disp, so knowing GZ curve for every displacement condition and heel angle is what matters. Curves of dynamic stability are mandatory to be developed and assessed also for commercial vessels, but even those are based on the integration of the static GZ curves.

The energy of the boat to resist capsize is given by the righting moment, absolutely, and, for two boats with a similar GZ curve, the bigger is able to better resist heeling forces. But as sizes and forms are so variable the only way of stablishing simple all around rules is to make the criteria "dimensionless", so avoiding displacement. As an example IMO rules are the same not matter what the size of the vessel (over 24 m length, although for smaller fishing vessels are also applicable, as recommended by IMO).

That's why what it is MANDATORY UNDER MOST REGULATIONS to analize the GZ curve to assess stability. All international criteria, including the RCD, stablish such criteria based on the analysis of the GZ curve. Even STIX uses only righting arms levers and areas under the GZ curve, but no values based on RM. But here, contrary to what happens with commercial vessels, the size of the boat is introduced in the criteria: Length roles a very important part, as the first term of equation by itself depends only on it and has the bigger weight in results (so favouring size), and displacement is thoroughly used around to calculate remaining STIX factors.

On the size of vessels and stability problems related, maybe you would like to read something I've wrote about commercial fishing ones at: http://www.gestenaval.com/estabilidad.htm

I perform many dozens of stability tests and assessements all years, including RCD ones. As a matter of fact I earn my life with this. Excuse me for sounding disagreeable, but honestly I'm upset with you, because several times you have contradicted my posts as if I were not knowing what I'm talking about. You have even told that to me, word by word. I have been polite to you up to now, what you have not been to me. Or that I understand.

The least I could have said to you is that you sound to me like an 'aficionado' having read some ideas here and there, but without a deep knowledge of matters. That's not bad, it happens all the time to everybody when acting out of his/her field of expertise, including myself. What is annoying is to cheat professionals with irrespetuous statements like I understand you've done in several ocasions. I have not said this to you before and I regret to have to say it now, but maybe it's better to clarify things. Sorry.

Cheers.

Vega

09-10-2006, 03:22 PM

Vega,

This may again be too far of a generalization but would you suppose that a finer hull will require more ballast than a beamier variant due it's diminished positive rm curve to be seaworthy and comfortable?

I suppose that by finer you mean a narrower boat?

If it is the case I would say yes, if it has not really to do with comfort. The narrow boat will be more comfortable, but to carry the same quantity of sail (to have the same RM between 10º and 30º of list) of the beamier boat, the narrow one will have to have more ballast.

That's why in a lot of modern boats (that are beamier) the Ballast/Displ. ratio can be less than 30% while on old narrow boats that ratio was between 40% and 50%.

Generally speaking, it is also why modern boats are lighter, faster and more uncomfortable than older boats. Unfortunately modern boats tend also to have a worst AVS and a bigger negative stability.

RHough

09-10-2006, 03:25 PM

Slightly off topic perhaps, for that I'm sorry. :)

Where might I find statistics for boats that capsize or pitchpole while NOT racing?

Of the cases that sailboats that capsize or pitchpole while not being pushed under marginal conditions (racing), how many of them could be prevented by a decent grasp of weather, good forecasting, and a bit of seamanship?

In other words, how remote is the possibility that a cruising sailboat will be in danger of capsize?

In my mind there is a similar situation with autos. There is a large effort to increase the chances of survival *after* a crash, but little effort to improve the crash avoidance ability of either the vehicle or the driver.

Taken to extremes, that would mean that less attention would be paid to seamanship in a boat with a favorable STIX number. This is proved daily by the driving behaviour of people in "crash proof" cars.

I'm all for not selling boats that will sink or capsize on their own after little or no error is made by the crew, but rules and regulations that would force boats to be built that no idiot could capsize make no sense. Sounds like we are going to see some pretty dull boats. :(

Vega

09-10-2006, 03:53 PM

I'm all for not selling boats that will sink or capsize on their own after little or no error is made by the crew, but rules and regulations that would force boats to be built that no idiot could capsize make no sense. Sounds like we are going to see some pretty dull boats. :(

No, it’s not about that. A Bavaria 30ft, is certified as a Class A boat, and that is the ultimate category, meaning Oceangoing boat. It has not really to do with excessive protection but with the possibility of giving to the buyer a valuable information about the seaworthiness of the boat he is interested in, and I mean the STIX number, and that one is not even compulsory on the boats catalogue (it should be in my opinion).

Guillermo

09-10-2006, 04:47 PM

Interesting to note that the MCA at its Marine Guidance Note 280 (M) "Small Vessels in Commercial Use for Sport or Pleasure, Workboats and Pilot Boats – Alternative Construction Standards" stablishes two "Permitted Areas of Operation" for RCD's Design Category A. One of them is Code "0", allowing boats unrestricted area, and the second one is Code "1" that goes up to 150 miles from a safe haven. It depends on the range of stability of the vessel. This is applicable only if RCD Category assessement has ben done using Options 1 or 2 of Section 6.1 of ISO 12217-2, this is, performing Stability Tests.

They categorize RCD's Category A into two zones/codes, as above mentioned, category B into two zones/codes and Category C into three zones/codes. So there is at least a national authority who thinks RCD's categorizations are not enough and need a deeper and more careful one, including further stability criteria.

In Spain, France and Portugal also exists this further categorization, by means of the so called 'sailing zones'. I do not know the criteria for Portugal or France, but in Spain authorities only consider the safety equipment carried aboard to fix the 'sailing zone' asigned to every particular boat, not extra stability requirements.

Here the general stability criteria used (sailing monohull) by the MCA:

1.- the area under the righting lever curve (GZ curve) should be not less than 0.055 metre -radians up to 30 degrees angle of heel and not less than 0.09 metre - radians up to 40 degrees angle of heel or the angle of downflooding if this angle is less;
2.- the area under the GZ curve between the angles of heel of 30 and 40 degrees or between 30 degrees and the angle of downflooding if this less than 40 degrees, should be not less than 0.03 metre - radians;
3.- the righting lever (GZ) should be at least 0.20 metres at an angle of heel equal to or greater than 30 degrees;
4.- the maximum GZ should occur at an angle of heel of not less than 25 degrees; and
5.- after correction for free surface effects, the initial metacentric height (GM) should not be less than 0.35 metres.

(Interesting to note they coincide, almost textually, with IMO's fishing vessels stability criteria).

The GZ curves should have a positive range of not less than the angle determined by the formula 90+60x(24-LOA)/17, for Codes "0" and "1", and or 90°, whichever is the greater.

In the damaged condition, the residual stability should be such that the angle of equilibrium does not exceed 7 degrees from the upright, the resulting righting lever curve has a range to the downflooding angle of at least 15 degrees beyond the angle of equilibrium, the maximum righting lever within that range is not less than 100mm and the area under the curve is not less than 0.015 metre radians. This damage should not cause the vessel to float at a waterline less than 75mm from the weatherdeck at any point. Proposals to accept reduced freeboard or immersion of the margin line may be accepted subject to special consideration.

Curves of statical stability (GZ curves) should be produced for:-
1.- Loaded departure, 100% consumables;
2.- Loaded arrival, 10% consumables;
3.- Anticipated service conditions; and
4.- Conditions involving lifting appliances (when appropriate).
In addition, simplified stability information in the form of a Maximum KG Curve should be provided, including a worked example to illustrate its use.
Maximum free surface moments should be included within the Loaded Departure condition

Guillermo

09-10-2006, 05:49 PM

Where might I find statistics for boats that capsize or pitchpole while NOT racing?
You have something here, although probably data are mixed:
http://www.rina.org.uk/rfiles/HISWA/1994/Investigation%20of%20minimum%20stability%20requirements%20for.pdf
Scroll down for table number 2.

There is also an interesting list of boats' data (Table 3) of which more than 5 units were built, having had no stability related problems. There we can ascertain how AVS is bigger for the smaller boats and lower for the bigger.

Seafra

09-11-2006, 03:47 PM

I suppose that by finer you mean a narrower boat?

Yea, that's what I meant. I thought "finer" was the correct term, but I'm relatively new.

If it is the case I would say yes, if it has not really to do with comfort. The narrow boat will be more comfortable, but to carry the same quantity of sail (to have the same RM between 10º and 30º of list) of the beamier boat, the narrow one will have to have more ballast.

That's why in a lot of modern boats (that are beamier) the Ballast/Displ. ratio can be less than 30% while on old narrow boats that ratio was between 40% and 50%.

Generally speaking, it is also why modern boats are lighter, faster and more uncomfortable than older boats. Unfortunately modern boats tend also to have a worst AVS and a bigger negative stability.

Yea, that confirms the imrpessions I was getting comparing classically designed boats to more modern production boats. Often boats of the same length can differ by 2' or more in beam.

I have to admit, beamier boats make sense for weekender or a cabin cruiser where cabin space and speed are probably the more sought after virtues. Alternatively, for an ocean cruiser, the seagoing comfort of a "narrower" hull and the safety factor seem to be essential.

Additionally, wouldn't a narrower hull of similar design to a beamier cause less turbulence? Or would the increase in draft due to smaller displacing surface cause more drag?

Vega

09-11-2006, 06:40 PM

I have to admit, beamier boats make sense for weekender or a cabin cruiser where cabin space and speed are probably the more sought after virtues. Alternatively, for an ocean cruiser, the seagoing comfort of a "narrower" hull and the safety factor seem to be essential.

Well, I guess you get me wrong. I don't think that good modern boats, what we have being calling beamier boats are inadequate to cross oceans, if they are designed for that. They can be also a safe boat, with a huge positive stability (much bigger that in a traditional narrow boat) and that without compromising an adequate negative stability.

I am not saying that I don't like "old" narrow boats. I like all of them (modern and old), if they are nice and well designed. I like the comfort and the easy movement of a heavy displacement narrow boat, but I like also the speed and the fun of helming a very fast boat.

It's a little bit like the difference between crossing America in a Mercedes or in a Ferrari.
Sure, the Mercedes is a lot more comfortable, but if you like driving, the Ferrari is a lot of fun. Of course, for many, a Ferrari would be unbearingly uncomfortable... and of course, if you drive the Ferrari at 140m/h, and the Mercedes at 70m/h, you will take more risks in the Ferrari.

That doesn’t mean that the Ferrari is more dangerous. If you drive both cars at the same speed, probably the Ferrari would have a better dynamic safety (safer while in movement) and the Mercedes a better passive safety (if you crash).:P

I think it is a bit like that between an old good traditional ocean cruiser and a fast good modern ocean cruiser, being the crash a capsizing, except that you don't get tickets for speed at sea.:D

I am not really talking about Beneteaus, I am talking about boats like the Lansart 47, the new French coqueluche. Take a look:

http://www.lansart.fr/index.html

http://www.guillaumeverdier.com/index.php?page=34

truemorc

09-11-2006, 09:04 PM

Looks like a big sister to the new Class 40 boats (cruiser/racer version). I very much like the concept- I think this is the next 'evolution' of the modern open class racing designs into the cruising arena. But still am (atleast intuiatively) concerned about the inverted stability. I guess if there is enough wave energy to capsize it-so to to bring it back upright again?

JohnO

Guillermo

09-12-2006, 09:47 AM

To those interested in knowing how STIX shall be calculated, I attach an explicative text taken from "Principles of Yacht Design" (by Lars Larsson and Rolf Eliasson). Those formulae are the ones constant in the spreadsheeet I've posted before, which has been improved over the one originally posted by SailDesign.

Here an interesting article on sailboats' stability written by Matthew Sheahan some time ago:
http://www.yachting-world.com/yw/stability/stability97.pdf

And here a RORC's paper on STIX, RORC STIX, SSSN and some considerations on ISO/FDIS 12217-2
http://rorcrating.com/stix/stixpaper.pdf

From this last, commenting ISO/FDIS 12217-2 (Nowadays already ISO 12217-2):

Required angle of vanishing stability
Design category...Mass of Boat (kg).......Required angle of vanishing stability (φV(R))
A ..................... m > 3 000 kg ............φV(R) = (130 - 0,002 m) but always ≥ 100°
B ...................... m > 1 500 kg ...........φV(R) = (130 - 0,005 m) but always ≥ 95°
C .....................................................φV(R) = 90°
D .....................................................φV(R) = 75°

Examples of use.
1. Any boat with AVS equal to or greater than 75º satisfies the requirements for Design Category D.
2. Any boat with AVS equal to or greater than 90º satisfies the requirements for Design Category C.
3. The absolute minimum AVS for Design Category B is 95º.
4. The absolute minimum AVS for Design Category A is 100º.
5. A boat weighing less than 1500kg can never satisfy the requirements for Design Categories A or B.
6. A boat weighing less than 3000kg can never satisfy the requirements for Design Category A.
7. A boat weighing 5000kg has a required minimum AVS for:
Design Category B of: 130 - 0.005 * 5000 = 105º
and for Design Category A of: 130 - 0.002 * 5000 = 120º

(An extra corolary: All boats with Disp over 15 tonnes are allowed a minimum AVS of 100º)

Now you may think 100º and 95º are absolute minimums for categories A and B. Yes? Well: Not so. AVS can even be less than those figures. Let's see:
As per ISO 12217-2, point 6.3.2 "Alternative requirement for design categories A and B", boats may also be assigned to category A or B provided that certain limitations are fulfilled. Simplyfying here only the more relevant ones:
a) AVS ≥ 90º for category A, or AVS ≥ 75º for category B
b) when the swamped or inverted boat is totally inmersed, buoyancy is sufficient to support the mass of the loaded boat by a margin
c) watertight compartments used to provide buoyancy shall be constructed to watertightness degree 1 in accordance with ISO 11812 and hatches and doors satisfy watertightness degree 2 of ISO 12216
....
e) the recommended maximum wind strength for a given sail area shall be determined on the basis that the upright wind heeling moment in a gust of twice the mean wind pressure shall not be greater than the maximum righting moment at any heel angle.
....:eek:

Vega

09-12-2006, 10:52 AM

...- I think this is the next 'evolution' of the modern open class racing designs into the cruising arena. But still am (atleast intuiatively) concerned about the inverted stability. I guess if there is enough wave energy to capsize it-so to to bring it back upright again?

JohnO

I believe that the inspiration comes mostly from the Open 60, boats, the ones that are used in the Vendee Globe (solo race around the world without stops or outside assistance). The Safran, the boat that is going to be Skippered by Marc Guillemot in the next Vendee, is also a Verdier (and Van Peteghem , Lauriot Prévost) design.

After some major problems (some years ago) these boats have now severe safety rules. Minimum AVS is 127.5º and that is not bad even for a cruising boat.

If the Lansart has at least this AVS (and probably it will be even better) and is a strong boat, as it seems to be, it will be alright, even in a capsize....at least it will not be worst than the vast majority of ocean cruising boats that are in the market. Many have a lower AVS.

I will post a paper about how, taken in account previous accidents, these boats (0pen 60) have been made stronger, with new rule alterations, concerning safety (interesting paper).

http://www.sailing.org/meetings/2002november/papers/OC_03.pdf#search=%22vendee%20globe%20stability%20avs%22

http://www.marcguillemot.com/en/index.php?2006/06/02/35-safran-open-60-meets-the-scrutinizers

Guillermo

09-12-2006, 05:32 PM

Now let's swing the opposite side, on this STIX thing.
Following the wake of my last post, we see no boat under 3000 kg displacement may qualify for Category A under the RCD.
Means this Patricia Newman's "Gannet", a Macwester Rowan (http://performance.boatshed.com/viewboat.php?boat=22737) (6,8 m, 3100 kg), which is inscribed for the Jester Challenge (http://www.jesterinfo.org/index.html), can be categorized as being an ocean going boat? Displacement seems to be 3100 kg, but probably Mmsc is lower than 3000.... Is Patricia worried at all about this? (Most probably she's not! :D )

Is Roger Taylor similarly worried about his junk rigged Corribee 21, "Mingming"...? ( :D :D )

As the UK is a more civilized country than Spain, most probably Patricia and Robert will be at the line in 2010, gods willing. Authorities in Spain wouldn't let them go, because although being old boats not subject to RCD, they wouldn't be comfortable with the thing and they would ask for a RCD certification by a Notified Body. Most probably Gannet and Mingming would not quailfy...:(

Crag Cay

09-12-2006, 06:47 PM

The RCD has no bearing on the use to which a boat may be put. It is specifically stated that this is the case in the introduction to the directive:

"The directive does not include any navigation or usage rules and there is no link between the design categories and any such rules..."

The RCD is only relevant when the boat is first placed in the market. If we in the marine industry are unclear as to the scope of the directive and use it in reference to matters to which it does not pertain, we can not then complain when the bureaucrats seek to similarly misuse it and control our freedoms to use our boats in anyway we see fit. If Spain has already started to control your boating by using the RCD, then complain to the Commission in Brussels because it is illegal to do so.

Similarly, cross referencing the RCD with MCA regulations for commercial vessels again muddies the water. The MCA does have a legal mandate to control vessels, but only those in commercial use, so don't give them any encouragement to extend their control to pleasure boats.

There is more at stake here than a few degrees of stability or a little down-flooding. Some of us want to preserve a world where people have to right to sail the Atlantic in their 21 foot boats if they should so wish, or whatever. The world would be a poorer place without the Mini TransAt, Jester Challenge, OSTAR, AZAB, etc and we should not contribute to the pressures the organisers of these events feel by our misinterpretation of any regulations that do exist.

The RCD is a fact of life. As a free trade agreement it has simplified the work of a few large companies that sell boats throughout Europe. Whether it has contributed anything significant to the safety of the boating public is debatable. Better education would still seem to be a better course than increased bureaucratic control. But the RCD could mutate into something really horrible that would impact on all aspects of our sailing lives. So stop prodding it with sticks and leave it alone.

Guillermo

09-13-2006, 10:44 AM

"The world would be a poorer place without the Mini TransAt, Jester Challenge, OSTAR, AZAB, etc"

I totally agree with your feelings Crag, but unluckily RCD is already ruling our lives (as users) and not only manufacturers' or designer's.

I understand the state members in the EU have full power to enforce whatever rules within their own waters, just not contradicting EU's general normative. That's what's happening in Spain and other EU countries (I know about Portugal and France, but maybe others). Here we have quite a restricting normative and to go to sea you must fully license yourself and your boat to do so (Whatever the size, except auxiliaries under 2,5 m) and sailing or operation zones are asigned based in the Design Category and level of safety equipment carried aboard. So, at least in our country we have already the problem on our necks.

Maybe not so in the UK, as you have a boaters' strong opposition to new and upsetting rules (Because of your powerful associations like the RYA) and it seem you are being able to delay some things. But down here that's what we have.

I think we have no enough power or strength, whatever we do in these forums, to influence the future of the RCD at all. Lucky we were if we could! But this is a Boatdesign place, so I think it's the right place to discuss this kind of matters, with as deep a technical level as possible, trying to get knowledgeable people's diverse points of view and most welcome technical contributions. At the end, that's what these Forums are for!

Talking about this, I'd greatly appreciate NA's, designers and the lot of other knowledgeable people around here, to post their contributions on this STIX thing, discussing particular cases known to them or their general knowledge on the matter. As many tech info as we can share and discuss, supported on workable data, the more useful Boatdesign forums will be.

Cheers

Footnote: Crag, have a look again at my post #38, as I have tried to clarify its meaning.

terhohalme

09-13-2006, 10:58 AM

Mini transat boats are designed and built to EU category B since 1998.

Seafra

09-13-2006, 12:15 PM

Correct me if I'm wrong, but the two sides of the coin I see are this:

Mainland Europe tends to "protect people from themselves" by legislating and creating oversight. This creates branches of bureacracy who's purpose it is to make us safer through regulation.

Mainland America takes a more conservative stance of leaving people to their own devices to a certain extent. If you have the money, you surely can buy just enough bike or car or boat to get yourself into a lot of trouble. And you don't have to wear a helmet on that bike either, and your lisence only cost you $30 at the DMV. This is by no means the case everywhere here, nor does it seem it will be that way forever.

It's really a debate as to which is better. Given a more lax stance, you start hearing about accidental deaths and a poignant story will come out, everyone will be up in arms for more laws and regulation. On the other side, you may obtain a better safety record with more regulation, you exclude the squids and hooligans, but for many(including myself) the price of government involvement and exhaustive rule making(and the resultant enforcement and penalization) is too high to pay!

Crag Cay

09-13-2006, 12:31 PM

The US coastguard has the power to prohibit any vessel putting to sea if they feel it may endanger life. It also dictates the safety equipment you must carry and States requires all boats to be regestered.

No such regulations exist in most of Europe.

The really 'crazy' trans atlantic crossings to and from Europe (eg 10 foot long boats, pedelos, etc) either start from Canada or go to West Indies because such thigs are not allowed in the US.

The lack of helmet wearing on motorbikes is evidence of the power of lobby groups rather than some innate 'right of freedom'.

Guillermo

09-13-2006, 01:40 PM

Mini transat boats are designed and built to EU category B since 1998.
Are you sure? Their designed displacement is a mere 1050 kg (As per http://www.dixdesign.com/didimini.htm), so not reaching the mandatory 1500 kg. :confused:
Boats intended only for racing are not covered by the RCD rules....

Seafra

09-13-2006, 01:44 PM

The lack of helmet wearing on motorbikes is evidence of the power of lobby groups rather than some innate 'right of freedom'.

Yes, but the AMA appeals to the "right to freedom" when they make their pitches. ;) It's all about freedom...blah blah blah...my personal freedom. My personal freedom to encroach on your freedoms!

I'll talk motorbikes since that's what I know best. A person in America can go out and buy a motorcycle of any displacement and capability regardless of their personal capabilities. All that's required to be legal is to take a $5 written test and a skills test to become motorcycle certified on their already $30 lisence(yes, I did complain about the $30 when I paid it too). In Europe their is a strict tiered lisencing system based off engine CC and peak HP. Additionally, it costs incomparably more to become lisenced in Europe and more to insure(counter-intuitive though that is).

Safety data will show that riding in America is more dangerous due to the rarity of personal protective gear such as helmet, suit, gloves, boots, armor(it's not "cool":rolleyes: ) as well as the comparitively broad granted privilege to the public to drive. That being said, would I trade that for Europe's over regulation? Probably not.

But you're right, Crag- I have considerably less of a case to prove that tendency in boats.:)

Vega

09-16-2006, 05:56 PM

…..RM curve is not considered to calculate STIX, but GZ curve…

STIX is a development of SSS, but uses more detailed stability data, including some from a righting moment curve.
Excuse me, but that's incorrect. Probably a typo or the like. RM curve IS NOT used, but the GZ curve. Just have a look at STIX input data.

And here a RORC's paper on STIX, RORC STIX, SSSN and some considerations on ISO/FDIS 12217-2
http://rorcrating.com/stix/stixpaper.pdf

Guillermo, the ROC paper you have posted is exactly the same that I quoted, the one with the “Typo or the like”, the one that says : STIX is a development of SSS, but uses more detailed stability data, including some from a righting moment curve.

If you take a look at the formulas to calculate the STIX that you have posted, taken from "Principles of Yacht Design" (by Lars Larsson and Rolf Eliasson), you will see that both GZ and RM values are used and those values can be calculated or taken from the respective curves.

A RM value is needed for the Calculation of the knockdown recovery factor (FR). The RM value is used, as part of the calculation. This is a RM value - (GZ 90º* mMsc).

You have stated correctly that: “Righting moment is …”GZ * Disp” …and because mMsc is only the displacement (kg) in minimum sailing condition, You have a GZ*Disp, therefore a RM value that can be taken directly from the RM curve.

You need also a RM value to the calculations of the Wind Moment Factor (FWM). To calculate the Vaw, (that is needed to calculate the FWM), it is used, as part of the formula, the symbol GZd and that, according to the definitions contained in the paper, is the RM at the downflooding heel angle, another value that you can take from the RM curve.

The Gz curve is also needed to calculate the FDS factor.

(I have posted and zoomed the relevant parts of the STIX formula.)

So I guess that it can be said that both are needed and that the more correct statement is:

“STIX is arguably the most sophisticated stability screening tool yet available. ….
Since June 1998 all new recreational boats sold in the EU have been required by law (the RCD*) to have undergone a stability assessment with the preferred method being the application of ISO 12217. This means that all but a very few new monohull ballasted sailing boats sold in the UK (including all of those imported) should have had a GZ / RM curve generated, their displacement and AVS determined and a STIX calculated. “

This comes from a very interesting RYA paper and is an introduction to an even more interesting book, published by them about Stability ref (G23).

http://www.rya.org.uk/NR/rdonlyres/43D83922-ED3E-4D5D-BBCF-6A14AA352EFA/0/StabilityIntro.pdf#search=%22stabilityintro%20pdf%22

But this is of little importance; the main disagreement with you is related with this statement of yours:

The energy of the boat to resist capsize is given by the righting moment, absolutely, and, for two boats with a similar GZ curve, the bigger is able to better resist heeling forces.

And this statement is not completely correct. Length or the size of the boat has nothing to do with it. Displacement has.

For two boats with a similar GZ curve, the boat with more displacement is the one with a bigger RM, the one that is able to better resist heeling, or a capsize. That’s why smaller sailboats with a heavy displacement are many times more seaworthy than much bigger lightweight displacement boats.

For a similar GZ, the lightweight boat can have the double of the LOA of the heavyweight, but if the heavy one has more displacement, it will have a bigger RM and the force needed to capsize it will be bigger.

That’s why I can not agree with this:

In my opinion Avs … Being important, of course, ... it should be used not alone but in conjunction with GZ at 90º value. A high value here is to ensure that the boat is able to right herself from a knockdown to an angle of around 90º

And that’s why I have said:

I agree with you that the complementary information about the force that the boat is making to right itself after a knock down, the total force needed to capsize the boat, the AVS and the total force needed to bring it back from an inverted position, is an important one. Those are important figures to understand the boat, but you don’t get any real conclusions with GZ numbers or curves ...but only with RM curves, the ones that are made from the GZ, but that doesn’t give you abstract values .. but the real forces for that boat... The RM curve is the only that can give you the real forces that the boat can make to recover from a knock down or the force to resist an inversion.

Putting it in other words and quoting that RYA paper:

“For ocean-going and offshore yachts one of the most easily seen and meaningful aspects of a GZ curve is the AVS.

But a GZ curve and its AVS are by no means the whole transverse static stability story. A boats mass (displacement) is also very important.

A lever, when multiplied by the force pushing it, becomes a moment. With a boat the lever is the GZ and the force is the boat’s mass. So by multiplying GZ by the boat’s mass gives a righting moment (RM) curve.

As the area under this curve represents the energy needed to heel the boat, then for the same GZ curve, a boat of double the mass will need twice the energy to capsize (and twice the energy to re-right after capsize). "

http://www.rya.org.uk/NR/rdonlyres/43D83922-ED3E-4D5D-BBCF-6A14AA352EFA/0/StabilityIntro.pdf#search=%22stabilityintro%20pdf%22

Or in the words of Angermark Marin, the Architect of Malo yachts:

"we frequently notice that it is very easy to misunderstand the meaning of the usually published stability curve that indicates the righting lever ( G-Z ).

This curve alone is no measure of a yacht´s real stability.
…..
In fact it is the curve of righting moment that illustrates this capacity.

….A much better assesment of the real stability is thus to compare the curves of righting moment, and also look to the STIX number as defined in the ISO standard.….

Putting in their words, or mine, we all are saying the same thing and that is:

GZ values are only the size of ARMS at different heeling positions, and its value is given in Europe, in meters, and in the USA in feet.

A buyer, while comparing boats, will not certainly be interested in the sizes of arms (GZ values), but in the resulting moment (the force) that comes from applying a mass (displacement) to the size of that arm and those are RM values (forces), expressed in force units.

Furthermore, Guillermo, may I point out that in the parameters that you have posted for the Red and Blue boats referred by you as the 'OLD' RATIOS AND PARAMETERS, the values that are given for accessing the boat’s stability are RM values, and not GZ values.

BLUE's 'OLD' RATIOS AND PARAMETERS.

…Angle of Vanishing Stability AVS = 123 º
Roll Period T = 3,66 Sec
Roll Acceleration Acc = 0,07 G's
Stability Index SI = 1
Upright Heeling Moment UHM = 19074,33 Ft*pound
Heeling Moment at 1º HM1º = 697,53 Ft*pound
Dellenbaugh Angle DA = 27,35 º

RED's 'OLD' RATIOS AND PARAMETERS
..
Angle of Vanishing Stability AVS = 116 º
Roll Period T = 1,93 Sec
Roll Acceleration Acc = 0,3 G's
Stability Index SI = 0,47
Upright Heeling Moment UHM = 19635,03 Ft*pound
Heeling Moment at 1º HM1º = 1306,88 Ft*pound
Dellenbaugh Angle DA = 15,02 º

So I don’t real understand why you have replied in this disagreeable way:

Don't make me laugh. …Probably we are all stupid and do not know about our work. Please teach us. :rolleyes:

After all, it is not only in the “Old Ratio Parameters” that RM values are used to access the stability of a boat.

You can see that Dudley Dix uses RM values and RM curves in his site for giving to costumers the stability data of his designs, the same with Malo and with the Globetrotter 45 and so on.

Unfortunately not many like to publish in the internet the stability data of their boats, but that’s another story.

http://dixdesign.com/dix43sta.htm
http://dixdesign.com/cr33sta.htm
http://dixdesign.com/dix61sta.htm
http://www.maloyachts.se/Portals/0/STAB-40.PDF
http://www.sponbergyachtdesign.com/Globetrotter45.htm

I don’t understand also why you say this:

About the GZ and RM issue, I'm not sure if you fully understand stability issues.

The least I could have said to you is that you sound to me like an 'aficionado' having read some ideas here and there, but without a deep knowledge of matters. …What is annoying is to cheat professionals with irrespetuous statements like I understand you've done in several ocasions.

A good way of accessing the knowledge of a person on a subject, is reading what he posts about it. Everything I have said was backed up with quotations from BIG and respected names in the Sailboat industry and you have not contradicted them. Those quotations practically say the same I have said before in other words and very close words.

It seems to me that if you disagree, you have to explain why and contradict the quotations that I have posted for they mean exactly the same I have said; you haven’t done that….So I really don’t understand.

I guess that the other occasion that you say I have been “irrespetuous” to you was the one when I have strongly disagreed with you about an old boat being faster in light winds than a modern boat.

We were comparing two boats regarding their speed in lightwind situations. The old boat had a superior displacement, a bigger wetted surface, a smaller RM and a smaller sail area, than the new boat, and all these factors by a very substantial margin and you insisted that the old boat was faster.

http://www.boatdesign.net/forums/showthread.php?t=12193&page=6&highlight=light+winds

I think that you consider "irrespetuous" someone that disagrees with you, unless he is a professional and has a formal education, no matter if you are wrong or right.

Respectfully

Vega (Paulo)

terhohalme

09-17-2006, 03:37 PM

Sorry Guillermo, a little late but:

Look at R-2 - ELIGIBILITY on p. 14

http://www.classemini.com/download/2006_Guide_Mini_-_Website.pdf

Guillermo

09-17-2006, 05:07 PM

I think that you consider "irrespetuous" someone that disagrees with you, unless he is a professional and has a formal education, no matter if you are wrong or right.
Not so. I consider irrespetuous people who when somebody disagrees with them (like you've done) say things as: “You don't know what you're talking about”, “you are not being honest”, "you really don’t know much about sailingboats", "you utilize fallacious arguments", "you need to be always right" and the like.....Quite respetuous indeed!

About the GZ vs RM discussion, let's see if I'm able to make myself understand, because this is becoming ridiculous: When calculating a vessel's stability what we directly get from calculus is the GZ curve and not the GM one, which may be easily drawn afterwards based on the GZ curve. So, even of course RM enter some of the STIX formulas, we do not enter RM itself as input data, but separated in its two factors, GZ and displacement. Read again carefully my posts, if you're so kind, and think twice before asuming I'm stupid, please.

I would appreciate very much you being more polite when discussing, and more careful with your interpretation of what you read. If in doubt please ask, instead of scorning and asuming a patronizing tone. And please, It will be also very nice if you could avoid trying to teach me the very basics of boat's stability in the future. I don't recognize you with that ability. Neither about STIX. Only a few posts ago you even didn't know what FL, FB, FR and Vaw were.

Thanks in advance.

Guillermo

09-17-2006, 05:31 PM

Sorry Guillermo, a little late but:

Look at R-2 - ELIGIBILITY on p. 14

http://www.classemini.com/download/2006_Guide_Mini_-_Website.pdf

Thanks a lot, termohalme.
It surprises me, but I recognize I've never worked with MINI CLASS rules.
Anyhow reading carefully what is stated there: "...showing that the boat answers the requirements of the category of conception B" it may be very well that this does not imply boats have to be categorized as B, but only fullfilling its requirements (for sure except the displacement one). In fact racing only boats do not need to be categorizerd under the RCD. Could it be?

terhohalme

09-19-2006, 05:23 PM

In mini class prototypes yes, but if you read further:

"Production boats :
Production boats launched after June 16th, 1998 must be stamped "CE"
and classified in category of conception B."

Guillermo

09-20-2006, 12:31 AM

:confused: :confused: :confused:
I have to find out how this can be. Do you have a clue?

terhohalme

09-20-2006, 03:03 AM

Claus Riepe

09-20-2006, 04:27 AM

Terho:
I too am just looking at 6.3.2 .
Boats do not need to be heavy to get Cat. B.

But, I am unsure about the downflooding issues that go into STIX, especially when boats have quick draining recesses only. Can there be 'downflooding' into a quick draining cockpit at all? Downflooding itself is when water floods into a hull or bilge itself through gravity. So when you have a completely sealed hull cavity with just a quick (self) draining cockpit on top of it, i.e. above the waterline level, how can 'downflooding' occur at all, as the water would never enter the hull or bilge itself?

Likewise the downflooding angle. OK, in a seriously heeling boat some water may at some angle seep in into a small part of the cockpit which may at that time and heeling angle be -temporarily- below water surface level, but that water will automatically and quickly be drained out again as the boat uprights again.

To me, 'downflooding' means water getting right into a hull structure from where it cannot drain back out -quickly- automatically through own gravity. Boats with a completely sealed hull cavity and buoyancy to spare and with just a quick draining cockpit on top should not be subject to downflooding issues at all. Correct? -Or what do you make of it?

Claus

Guillermo

09-20-2006, 08:31 AM

Guillermo,
In EN ISO 12217-2 in item 6.3.1 there is a normal requirement of m>1500 kg in category B, but in item 6.3.2 is an alternative requirement without mass. So, the boat should be heavy enough with large varnish stability or a watertight floating one.

Terho
Yes, absolutely, thanks. I didn't realize, although I posted on 6.3.2 at this same thread. See http://boatdesign.net/forums/showpost.php?p=105071&postcount=36
How stupid I am! (Getting old...:( )

What is surprising here is that 6.3.2 requires a lower AVS (Only 75º for Cat. B!). Basically this point is applicable to boats able to float when flooded.

From MINI Class rules:

J-6 - BULKHEAD
A watertight bulkhead must be located between 5% to 15% of LWL aft of the perpendicular of the bow.
J-7 - CONSTRUCTION
J-7-a The boats must be seaworthy and watertight.
......
JJ-8 - HULL AND DECK OPENINGS
.....
J-8-b The hatch boards for the companionway and deck openings must
be watertight.

I understand the forward watertight compartment provides enough bouyancy to keep the boat afloat. Anyhow it will be a very life-threatening position to wait for rescue, if the boat is floating bows up. I mean, you should abandon boat and go into the liferaft, so what's the needing of a such a floatation for? ISO rules for swamped tests for recreational boats require a more or less level floatation when flooded. Do MINIS have extra floatation compartments to allow for this? Could you tell us more on the matter?
Thanks in advance.
Cheers

Guillermo

09-20-2006, 08:42 AM

...I am unsure about the downflooding issues...
Claus,
From ISO 12217-2:
Definitions.
.....
3.3.1 Downflooding opening: any opening (including the edge of a recess) that may admit water into the interior or bilge of a boat, or a recess, apart from those excluded in 6.2.1
.....
6.2.1.1 The requirements given below, and in 6.2.2 and 6.2.3, shall apply to all downflooding openings, except:
a) watertight recesses with a combined volume less than LhBhFm/40, or quick draining recesses.
.....

Cheers.

terhohalme

09-20-2006, 03:24 PM

Guillermo,

Perhaps the half sinked mini is a powerfull sea anchor for liferaft?

Can't tell, we need a mini sailor to tell us more.

Guillermo

09-20-2006, 05:57 PM

Perhaps the half sinked mini is a powerfull sea anchor for liferaft? :D

we need a mini sailor to tell us more.

Yeap. Any MINI sailor or designer out there able to help?

Claus Riepe

09-21-2006, 03:19 AM

Claus,
From ISO 12217-2:
Definitions.
.....
3.3.1 Downflooding opening: any opening (including the edge of a recess) that may admit water into the interior or bilge of a boat, or a recess, apart from those excluded in 6.2.1
.....
6.2.1.1 The requirements given below, and in 6.2.2 and 6.2.3, shall apply to all downflooding openings, except:
a) watertight recesses with a combined volume less than LhBhFm/40, or quick draining recesses.
.....

Cheers.

Thank you, but that is not the tricky bit.:

You may have missed 6.4.8, last sentence: There is reference to -large- 'openings' in general, not just to the clearly defined 'downflooding openings'.

Quick draining cockpits ARE clearly excepted from being 'downflooding openings'.
But it could be argued that they are still 'openings' in the sense of 6.4.8, so that in effect they WOULD return into the calculation of Downflooding factor and STIX, from which they were -at first glance- excluded through 3.3.1 icw 6.2.2.1 a).

This could well be just an editorial lapse of the ISO, or of its translation, but I am not sure, maybe it is intentional and relevant.

What would you say?

Claus

Guillermo

09-21-2006, 11:29 AM

Claus,
ISO 12217-2:2002(E) point 6.4.8, is about the calculation of the downflooding factor (FDF). Last paragraph from there:

"Φda1 is the angle of heel at which openings which are not capable of closure to tightness degree 3 of ISO 12216 having a combined total area, expressed in square millimiters (mm2), greater than the number represented by (50Lh^2) first become inmersed."

So a for a boat of Lh=12 m, all openings greater than 7200 mm2 (0.0072 m2), which's closuring device (If any) doesn't comply with required tightness degree, shall be checked for this.

Those are small openings, not big. Let's say a vent with a diameter of 96 mm, or two of 68 mm diameter flooding at the same angle, i.e. (So the word "combined" in the rule)

I'm not sure what you mean, sorry...:confused:

Claus Riepe

09-21-2006, 03:28 PM

Guillermo

09-21-2006, 05:07 PM

Guillermo:
No need to be confused.
Just take it that 'Greater than' means exactly that, 'greater than'.
Greater than -say- 7.200 sq mmtrs. means any opening GREATER than 7.200 sq mmtrs..
Not -as you surmise-SMALLER than 7.200.

Why do you think 6.4.8 applies for 'small openings' only? The opposite is true.

Claus
Claus, I don't follow you. I DID NOT say 'smaller', but 'greater' Please read again carefully. And if you take the care of working down numbers, you'll find that a 96 mm diameter opening has a GREATER area than 7200 mm2 (7238 mm2, to be precise. And two 68 mm dia. ones totalize 7263 mm2).
And those are small openings, in my opinion, the type of a deck mushroom vent which's watertightness degree doesn't fulfill level 3 requirements.
My understanding is that Φda1 is conceived for such types of openings. There's something similar at the rules for the openings of outboards' cables in outboard wells. But now I'm at home and do not have ISO book with me. On monday I'll check and post. I'll also check ISO 12216, were I think I'll find some extra support to this.
Cheers.

Vega

09-21-2006, 07:56 PM

Not so. I consider irrespetuous people who when somebody disagrees with them (like you've done) say things as: “You don't know what you're talking about”, “you are not being honest”, "you really don’t know much about sailingboats", "you utilize fallacious arguments", "you need to be always right" and the like.....Quite respetuous indeed!

Sorry not having replied more promptly, as I should, because what you are doing is not right.

… because several times you have contradicted my posts as if I were not knowing what I'm talking about. …. What is annoying is to cheat professionals with irrespetuous statements like I understand you've done in several occasions…
I would appreciate very much you being more polite when discussing…

You say that I have done that on other occasions, (I mean, contradicted and being "irrespetuous" to you), but obviously you are mainly saying that I have done it in this thread, otherwise it would not make any sense to say this in this thread.

To show that I have been “irrespetous” (disrespectful ?) to you in this thread, you seem to think that it is right to quote a serial of out of contest quotations from another thread, without any information of that fact, inducing that way, people to think that I have said those things in this thread.

Well maybe it is right by your rules of conduct, not by mine.

I will post the entire post where I have said those “irrespetous” things to you (the quotations you make).

I feel it is necessary, because it is the only way to put those quotations of mine in contest, and let people see what they really mean. Certainly I was not trying to insult you, only saying what I thought it was true, and explaining why.

Well I was hopping that you were mistaken in that weight...and I was diplomatically waiting for you to correct...but no, it seems that you are really talking about an old 50ft, 10 T cruising sail boat.

It can only mean two things: Or you honestly don’t know of what kind of boat you are talking about or you know and then you are not being honest in this comparison.

About the Beneteau:

Anyway you are not being honest when you say that the Beneteau 50 "is a...good performer in their time”. Or perhaps you really don’t know that the Beneteau Oceanis 50 is the floating condo from Beneteau, a slow boat in the Benetau range. And even so your numbers are not right, the boat weighs only 13T ( this is the light weight boat, but I believe the 10T of the other boat is also a light weight) and has some more sail than the one you have considered ( instead of 105, it has 115.8).

http://www.beneteau.com/ressource/documents/4165/B_oceanis50_230606.pdf

The only 50 ft Beneteau that can be considered a “... good performers in their time” is the new First 50. This one will displace 12.8T for 138.7 m2 of sail.

http://www.naucat.com/katalog/repDetalj.asp?id=1293

Of course, has this it a new boat, you can consider the older boat, the one this one replaces, the First 47.7, that has a displacement of 11.5T and 120 m2 of sail Area.
http://www.beneteauusa.com/sail/previous/first/477_intro.php

The Luders 50ft/10T:

Alfred Luders was a good naval Architect who has made racing boats and cruising boats. HIs most famous boat is American Eagle, a racing 12 mR that was the Americans cup challenger in 1964. The boat was modified for ocean racing by Ted Brewer and has won a lot of races, including the 1972 Sydney-Hobart.

http://www.americascupcharters.com/us21.htm

His most known cruising yachts were the Sea Sprite series.
http://www.seasprites.com/BoatsFrame.htm

A 50ft Luders with 10T can only be a racing boat. I have doubts that you can call that a cruiser-racer, (the boat you have posted is racing), and I seriously doubt that that boat has only 10T.

Typically, racing extreme boats of that time (60’s) with around 15m were the 8mR class boats, a kind of scaled down America cup boat (the 12mR class).

A typical boat of that class, probably from the same time of that 50ft Luders is the Olin Sthephens designed 8m Racing sailboat Iroquois, a 1967 boat with 14M, displacing 9.5T with a beam of 2.4 a draft of 2.0. They don’t say the sail area, but typically in the 8mR class, it is between 75 and 80 m2. This boat is a very competitive one and has won the 1984 8mR cup in Norway and the 1985 Sweden cup.

If a truly fast, 46ft top of the range, racing boat of that time displaced 9.5T, how do you think it is possible a 50ft cruising boat to displace only 10T?

These boats were so beautiful and gave so much fun that the class still exists, with new boats competing against old boats.

Even today, using modern building techniques (cold molded mahogany and epoxy vacuum techniques) it is only possible to make a 8m Racing class boat with 8.2T, like the Spazzo, (2000 world cup winner with a LOA of 13,4 m carrying 82m2 of sail) .

http://www.spazzo.de/specs.html

It is just not possible to have a wooden 50ft cruising boat in the sixties with 10T.

Of course that boat you have posted looks like a racing boat (and it is racing in the photo) and even so, comparing its appearance with the one of a 8mR class boat, I would say that it must have more than 10T.

Only you, Guillermo, would try to compare a racing design from the sixties with a relatively slow fat condo from nowadays to see how they compare in their light wind performances saying :

“Just to compare old and new boats:
Fisrt, let's compare boats with similar overall length and recognized as reasonably good performers in their time.”

How about to compare 50ft modern fast cruising boats with old fast cruising boats and 50ft modern race boats with old fast race boats?

Here you have my contribution: This is a good fast old 50ft cruiser (Luders designed) sailboat with 13 T. They don’t say the sail area but in that time a cruiser had relatively small sails, by modern standards.

http://www.yachtshare.com/boats-for-sale/Luders_Yawl_2007_50_4604.pdf

Guillermo, I like boats and I like to discuss boats, but I don’t like pointless arguments nor I discuss to win or lose an argument, just to learn and to share what I know.

Obviously it is not your case. It is not the first time you utilize fallacious arguments to prove your point even if they make no sense at all (comparing an old racing boat with a modern slow cruising boat, regarding light winds performance).

I don’t know if you need to be always right or if you really don’t know much about sailingboats. For one that can go so low on devious arguments, you assume many times a patronizing tone, like in the post 63, while you say things that have no sense at all, like this:

I think this is a risky statement, being said like that. I'm not sure what you mean. Initial stability depends mainly on forms....

It depends on the type of hulls Guillermo:rolleyes: ...

Then in a 8mRacing 47ft boat (like the one posted) with a beam of only 2.5m and very little form stability, do we assume that it must have a very limited sail carrying capacity (initial stability)? :confused:

How the hell do you think it gets the initial stability to carry 93 m2 of sail? Certainly not in its form stability, but in its low center of gravity.

Please, Guillermo, try to be a little more modest and don’t assume other people don’t know what they are talking about. It is not agreeable and obviously it is not always true.;)
http://www.boatdesign.net/forums/showthread.php?t=12193&page=5&highlight=light+winds (post 66)

About being Polite…well, Guillermo, I have tried, especially in this thread.

Guillermo

09-23-2006, 05:29 AM

Paulo,
As you've probably noticed, I was very upset with that your scorning post, and ceased answering you because I didn't want going down into that level of personal aggresion discussion. After summer I tried to be nice to you again, just for the sake of these forums, but I realize it's of no use. You came back in with the same kind of attitude. Well, I'm not available to this nonsense anymore.

Guillermo

09-23-2006, 05:58 AM

Now let's analize how STIX varies with the several input data. A kind of "what if" game. I'll use the data of the RED boat.

Originally we had:

Vessel Name: “RED MODEL” (LIGHT)

INPUTS

Overall Hull Length 11,98 m
Length Waterline 10,57 m
Flooded Buoyancy (Y/N) N
Beam Waterline 3,27 m
Beam 4,1 m
Displacement MSC 5165 kg
Displacement Max 6190 kg
Height of CE above DWL 6,87 m
Height of CLR below DWL 0,95 m
Angle of vanishing stability 123 deg
Downflooding angle 137 deg
GZ at downflooding angle -0,23 m
GZ at 90 degrees 0,58 m
Sail Area 71,1 sq.m
Area to flooding (Agz) 74,46 m.deg
Area to AVS 75,56 m.deg

RESULTS

Base Length Factor (LBS) 11,040
FL 1,001
Displacement Length Factor (FDL) 0,914
FB 2,519
Beam Displacement Factor (FBD) 0,815
FR 3,066
Knockdown Recovery Factor (FKR) 1,146
Inversion Recovery Factor (FIR) 1,010
Dynamic Stability Factor (FDS) 1,381
Vaw Not aplicable
Wind Moment Factor (FWM) 1,000
Downflooding Factor (FDF) 1,250
Delta 0

STIX 38,838

DESIGN CATEGORY A
Wave height max 7 metres
Windspeed max. Force 10

Now increasing LOA from 11,98 m to 13,0 m (just increasing overhangs to an oldies style one), we realize STIX (you may check it with the spreadsheet I've posted before), instead of increasing, DECREASES from 38,838 down to 38,771
Not a big deal, you may think, but in the limits this can make a long overhangs boat not categorizable under Cat A, while an squared ends one could pass (with all it's marketing consequences).
But it will have not only marketing consequences, but also safety ones, because surviving in rough weather conditions, in situations where a boat is heeled 90º or more, the boat with longer overhangs probably is able to defend itself better than a squared one. Rolf Eliasson states that for those conditions probably is LOA what should be doubled in the formula and not LWL.

(To be continued...)

Vega

09-23-2006, 09:27 AM

Paulo,
... I was very upset with that your scorning post... I didn't want to enter into that level of discussion.

Guillermo, I agree with you. There is no pleasure in replying to "scorning posts", even if a reply is needed, just to show that there was no reason for that “scorning”.

But may I remind you that in this thread it was you the only one who made scorning comments:

Don't make me laugh. ...Please teach us. :rolleyes.

I hope that this disagreeable matter is finished, because I would like very much to have time to post about the subject of this thread: The STIX numbers.

No hard feelings,

Vega (Paulo)

Guillermo

09-24-2006, 02:41 AM

Thanks, Paulo.
I recognize I overreacted. Let's go boating again.
Cheers.

Guillermo

09-25-2006, 08:44 AM

Claus,
6.4.8 states that Φd shall be taken as the least of the following: Φdc, Φdh and Φda1. This last I've already posted what it is. The other two:

Φdc: Downflooding angle to cockpits that are not quick draining according to ISO 11812
Φdh: Downflooding angle to any main access hatchway.

Degree of watertightness 3 is "protection against splashing water", as known.

This, united to the relatively small area required, is what makes me think Φda1 relates to small openings. But I may be wrong, of course. In my opinion the sense seems to be this one, but I agree with you that redaction is not clear enough.

By a quick look I have not find a clue neither in ISO 12216 nor in ISO 11812

I would love to know other people's opinion or firm knowledge on this. Anybody?

On my side, I'll put the question to a Notified Body, to find out how they understand this. If I get an answer, I'll post it here.

Cheers.

Vega

09-25-2006, 01:29 PM

Guillermo, I am relieved. I believe that both of us "fervemos em pouca água" (and I really don't know how to put this in English), so I believe that that the guilt in what concerns overreacting, is not only yours. I guess that in what concerns temper, we are not very different. :p

Cheers

Paulo

Guillermo

10-15-2006, 05:47 PM

I would very much appreciate if somebody could provide accurate info on the Beneteau OCEANIS CLIPPER 44 CC. I've been sailing one of those for several days in the open waters of the Canary islands and I would like to analize her numbers against my sailing experience. Specifically, stability data and curves will be most appreciated.

A first glance to numbers, as provided at http://www.beneteau-owners.com/
and http://www.beneteauusa.com/sail/previous/center/44cc_intro.php
but using I,J,P,E from the Oceanis 440, gives the following:

Lh = 13,2 m
Lwl = 11,2 m
Bmax = 4,25 m
Bwl = 3,83 m (as 0.9 Bmax)
Draught = 1,75 m
HD = 0,75 m (guess)
Disp = 12598 kg (full load, 6 crew)
Ballast = 3100 kg
Sail area = 75,7 m2
Power = 72 HP

Length/Beam Ratio L/B = 2,87
Ballast/Disp Ratio W/Disp = 0,25
Displacement/Length Ratio D/L = 250,11
Sail Area/Disp. Ratio SA/D = 14,21
Power/ Disp. Ratio HP/D = 2,59 HP/ton
Hull speed HSPD = 8,12 Kn
Potential Maximum Speed PMS = 8,23 Kn
Velocity Ratio VR = 1,01
Capsize Safety Factor CSF = 1,84
Motion Comfort Ratio MCR = 32,91
Heft Ratio HF = 1,03
Angle of Vanishing Stability AVS = 116 º
Roll Period T = 3,23 Sec
Roll Acceleration Acc = 0,11 G's
Stability Index SI = 0,76

As per a first estimative, the STIX should be around 60, so well into the A Category. As said, more accurate info will be greatly appreciated.
Thanks in advance.

Vega

10-15-2006, 06:47 PM

ISO 12217 STIX: 34

AVS: 110

I don't know if I can find a RM curve. The Avs and the STiX are on the low side.

Cheers

Guillermo

10-16-2006, 03:12 PM

Thanks, Paulo.
Those STIX and AVS seem to be too low for such a boat. Did you get them from the manufacturer/designer?

Vega

10-16-2006, 07:03 PM

Yes the data is provided by the manufacturer and I also think that those numbers are low for a 44ft boat.

Unfortunately it is not the only case:

BAVARIA 42 ISO 12217 STIX: 36
BENETEAU CYCLADES 43 STIX: 36
DISCOVERY 55 STIX: 37
BENETEAU 50 AVS 109 ; ISO 12217 STIX: 41

To have a STIX of 60 in the 45ft range you would have to look at another kind of boats, for instance to the Malo 45 (STIX: 62).

Cheers.

Guillermo

10-17-2006, 01:22 AM

This supports my understanding that a lot of pressure was done from manufacturers when the stablishing of the STIX thing. Many boats nowadays categorized as being "A", do not fullfill the requiremnts for proper blue water cruising, as I understand it.

After logging 300+ miles in the Canary islands with the Oceanis 44 CC, in open waters and nice weather conditions, I have to say she has quite uncomfortable movements. Measured rolling period aboard is around 3 seconds, which agrees quite well with the estimated one. An this for a boat with a 4,25 m breadth.
Sleeping in the forward bunks and even in the cockpit is quite uncomfortable even with the slightest chopping/swell, both at sea or at anchor. And this for a very heavy full load cruising condition (My friend carries a lot of gear aboard, we had full tanks and and we were 5 big boys), so probably being the boat close to a 13 tonnnes displacement.
If we work numbers for what Mmsc could be (around 10842 kg), we get:

Ballast/Disp Ratio W/Disp = 0,29
Displacement/Length Ratio D/L = 215,25
Sail Area/Disp. Ratio SA/D = 15,7
Motion Comfort Ratio MCR = 28,33
Heft Ratio HF = 0,89
Roll Period T = 2,84 Sec
Roll Acceleration Acc = 0,15 G's
Stability Index SI = 0,67

So even worse than the ones I posted previously.

Further on, the steering system is not enough safe, in my opinion, with the autopilot disengaging the wheel. The keel configuration (low draught, winged) and the assimetrical hull lines when heeled, make for an excessive leeward walking. The low freeboard at the bow, along with the assimetrical heeled hull, makes the bow very wet, embarking green water on the forward deck when beating to winward, even with as low as 0,7-1 m waves.

It's amazing a boat this size and configuration can have an STIX as low as 34. In my humble opinion it should have been categorized as "B" at its most. I agree with Eliasson's statement about being 40 a much better lower limit for Category A. By the list you have posted, only the Beneteau 50' would have fulfilled the requirement (!). I also agree with him it makes not sense to favour plumb bows. A well conceived reserve of buoyancy forwards is important. Interesting to realize now that freeboard at the bows is not taken into account to stablish the STIX number, which is supposed to give a clue to the seaworthiness of a boat.

Being totally honest, I think most of this kind of boats should be categorized as 'C'. Nice weather coastal cruising 25 miles away from land (What some EU countries legislation allows for this category) is quite enough for them.

Vega

10-19-2006, 07:05 PM

This supports my understanding that a lot of pressure was done from manufacturers when the stablishing of the STIX thing. Many boats nowadays categorized as being "A", do not fullfill the requiremnts for proper blue water cruising, as I understand it.

After logging 300+ miles in the Canary islands with the Oceanis 44 CC, in open waters and nice weather conditions, I have to say she has quite uncomfortable movements. .....

Being totally honest, I think most of this kind of boats should be categorized as 'C'. Nice weather coastal cruising 25 miles away from land (What some EU countries legislation allows for this category) is quite enough for them.

Guillermo I was waiting for someone to reply, not wanting to turn this into a dialogue...but as no one has posted, I would like to comment on your statements.

I agree with you, without going to the point of saying that this boat should be classified as class C.

I have already said that for me, one thing is seaworthiness, other is comfort and the two are not necessarily linked.

For example, take a look at the STIX ,AVS, and seaworthiness of these very sporty and uncomfortable cruiser-racers:

Elan 45 : Stix 44, AVS 124 ;

Beneteau First 44.7 : Stix 41, Avs 130

X-Yachts IMX-45 : Stix 46, Avs 124

X-Yacht IMX-40 : Stix 47 Avs 132

J 133: Stix 46, Avs 130

Why does the Beneteau Oceanis 44 cc have such low numbers on seaworthiness? The Oceanis 411 is smaller and has a higher Stix (37). At first sight, that doesn’t seem to make much sense.

You know, some years ago, when Bavaria 40 Ocean came out in the market I was interested in it. It looked like an Oceangoing boat (very much alike the Halberg-Rassy 40), so I got some detailed information only to be vastly disappointed. That boat had the same hull as the “normal 40”, the same ballast, only the interior and upper deck were different.

As the boat had more freeboard and more weight up, it would have a higher center of gravity, compared with the “normal version” and it would not be more seaworthy, but less. Ridiculous!:rolleyes:

I think that with the Oceanis 44cc it happens exactly the same.

This time, about comfort, in what regards the Oceanis 44 cc, I fully agree with you. That boat is sold under the image of a comfortable oceangoing cruiser, so it should be comfortable and seaworthy. It is like selling a car that looks like a Mercedes, has the safety of a cheap Fiat and it is as uncomfortable as a Ferrari.:p

Cheers

luso

10-21-2006, 08:44 PM

Hello,
You guys are very knowledgable.So I wonder if you could help us. We have a 48' schooner metal hull made by Carof design in 87. I believe the model name is Lex Erterna. We could never find any information about her estability and I 'm very curious about it.We've been refiting her for the past 6 years. We are getting close to being ready to leave port and sail around for awhile. I am always wondering about her limits of estability. Would she flip back? How long would that process take? How far can she heel? Maybe you could help us answer these questions? Here goes some info on her:
Hull 48'
loa 42'
beam 14.5'.
hard-chine,
deadwood cut away type of keel,
freeboard 5',5"
displacement 30.000[I believe in metric]
We would appreciate very much any info you could give us
thank you, Luso

Vega

10-22-2006, 12:41 PM

Would she flip back? How long would that process take? How far can she heel? Maybe you could help us answer these questions? Here goes some info on her:
Hull 48'
loa 42'
beam 14.5'.
hard-chine,
deadwood cut away type of keel,
freeboard 5',5"
displacement 30.000[I believe in metric]
We would appreciate very much any info you could give us
thank you, Luso

Hey Luso, welcome (are you really a Luso descendent?)

You don't give me all the data that it is needed to make an approximate calculation of the AVS or LPS . The ballast is needed.
But I will give you the means to perform an approximated calculation.

Read this page for definitions:

http://dan.pfeiffer.net/boat/ratios.htm

"The limit of Positive stability (LPS) is the roll angle at which a boat will no longer right itself and become inverted (capsized)".

and this one for understanding the calculation and error margins:

http://dan.pfeiffer.net/10m/avs_calculation.htm

And here you can perform directly the calculations, using a calculator:

http://www.sailingusa.info/cal__avs.htm

Cheers

Guillermo

10-22-2006, 01:59 PM

I am always wondering about her limits of estability. Would she flip back? How long would that process take? How far can she heel?
luso:
If you have a serious concern about her stability, the best thing you can do is to hire the services of an NA to perform a proper stabiility experience and then, armed with body lines (do you have them?), general arrangement plan, sails plan and tanks capacities tables, do all calculations needed. All approximate methods are that: approximate; and some times grossly inacurate.
Anyhow if you provide me with the following:
Lwl, Bwl (if known), medium load displacement, ballast, hull body draught, total draught, sail area (only the triangles, not the full size of the sails) and the heeling arm, this is the vertical distance between sails center of effort and the lateral center of resistance of the hull (your best estimative), I can provide you with the following estimated ratios, parameters and stability data:

Length/Beam Ratio
Ballast/Disp Ratio
Displacement/Length Ratio
Sail Area/Disp. Ratio
Hull speed
Potential Maximum Speed
Velocity Ratio
Capsize Safety Factor
Motion Comfort Ratio
Heft Ratio
Angle of Vanishing Stability
Roll Period (You can easily check this by yourself)
Roll Acceleration
Stability Index
Upright Heeling Moment
Heeling Moment at 1º
Dellenbaugh Angle
Initial Metacentric height
Righting Arm 10º
Righting Arm 20º
Righting Arm 30º
Vertical COG position

As said before, results may or may be not be accurate, but at least will give you a clue.

Also photos and drawings from her would be of great help to better estimate some measurements.
Cheers.
Guillermo

Guillermo

10-22-2006, 02:11 PM

luso

10-22-2006, 08:31 PM

Hello Guys .
Thank you for your interest in our delema.
I've been to those sites Vega suggested and by those calculations I did I came with the stability value of 224.59 and the angle of vanishing stability of 111.86. What do does those values mean [ if they are correct]?
Just in case you guys have the time to help me I have some mesurements of the boat.
LOA= 14,93 MTS
LWL= 13,12 MTS.
B= 4,60 "
BWL= 4,06 "
DWL= 2,00 "
MAX GROSS WEIGTH = 23,000 KG
BALLAST= 7,000 KG.
HULL SPEED = 8 TO 9 KNOTS
L/B = 3,24 MTS.
LWL/BW = 3,23 MTS.
SAIL AREA+ 1,200FT SQ. [ I = 23 MTS. J=5.5MTS. P=16 MTS. E= 4MTS.]
HULL DRAFT AT BEAM OF THE HULL IS = 1 METER
RUB RAIL IS = 1,30 MTS.
I will try to insert some photos .
thank you

Guillermo

10-23-2006, 03:57 AM

luso:
I'm not sure about that 224.59 figure meaning. The +/- 112 AVS is, of course, an estimated one and seems low for an oceangoing cruiser. As your boat does not have big superstructures, probably the real AVS will not be far away from that. Anyhow it's important to know what you mean with 'Max Gross Weight'. Is it the estimated full load displacement? Or is it the weight of the finished construction, but without fuel, water, storages, crew, etc? (What is called the lightship condition). Please clarify this.
Also: In the sail area you include both mast's sails? If yes, Could you provide the areas separately?
Tonight I'll work at home on the numbers you provide and be back to you.
Cheers.

Guillermo

10-23-2006, 04:09 AM

Groupe Bénéteau announces two new boat lines:
http://www.ibinews.com/ibinews/newsdesk/20060920145255ibinews.html
I'll try to analize the STIX of the announced Oceanis 50 whenever the technical info comes available (Let's hope they'll provide enough!).

Vega

10-23-2006, 11:03 AM

Luso, why don't you ask the correct numbers to Mr Caroff?

After 30 years in business, he is still producing some nice work, like the Atlantis.

http://caroffduflos.free.fr/

Your hull seems to be a nice one.

About those numbers, like Guillermo, I don't know how you have got what you call "stability value" and therefore I don't know what it means.

The 112º AVS means that the boat could lie down on its side (at a 90º angle) and still flip back. The boat will not come back only when it roll further than 112º.

Of course, it will not be exactly like that, because in the calculation you have made, the weight of the masts and sails is not taken into account, and that calculation is only an approximated one anyway.

If I was you I would e-mail Mr. Caroff.:)

cheers

luso

10-24-2006, 02:21 AM

The calculations I came up with are from the site Vega suggested
http://www.sailingusa.info/cal__avs.htm.
In regards to the sails, the plan is 325 square feet per mast + 1200 for the genoa and 110 for the yankee. Today a wrote to Carof to confirm the displacement number. Hopefully he will respond soon. I'll let you know what he says. Thanks, Luso

Guillermo

10-24-2006, 05:15 AM

Here again the STIX calculator with an slight improvement. I'll also upload it at the Library pages.
Cheers.

Guillermo

10-24-2006, 05:39 AM

luso,
With the data you provide and assuming a 127 sqm area (main mast triangles plus a mizzen 32 sqm), I get the following numbers:

Ballast/Disp Ratio W/Disp = 0,3
Displacement/Length Ratio D/L = 284,06
Sail Area/Disp. Ratio SA/D = 15,99 (nice)
Hull speed HSPD = 8,79 Kn
Potential Maximum Speed PMS = 9,1 Kn
Velocity Ratio VR = 1,04
Capsize Safety Factor CSF = 1,63 (nice!)
Motion Comfort Ratio MCR = 46,7 (nice!)
Heft Ratio HF = 1,42 (nice!)
Angle of Vanishing Stability AVS = 118 º (low, but better than 112º)
Roll Period T = 4,62 Sec (nice!)
Roll Acceleration Acc = 0,06 G's (nice!)
Stability Index SI = 1 (nice!)

So it seems to be a safe, fast and with comfortable movements boat, pretty able for ocean passages with short crews. The only concern is the low AVS number, although probably the real number may be higher. Interesting to know numbers from the designer.
Cheers.

Vega

10-24-2006, 06:37 AM

Guillermo, probably the deck-saloon configuration will increase the AVS to something like 130º, and that is not a bad value.

About the STIX calculator, are you using the Formula that was given by Larson and Eliason or the one given by Miller?

I know, the Formula is just one, but both sources are credible and the first expression (for boats with > 10m) is different:

(7+2.25XLbs) and (8+2.2XLbs)

I don't know what is the right one (probably one was an initial experiment and the other the definitive version and the one in use). I will need sometime to find out the correct one. Perhaps you can check it out for me on the official papers that define Iso 12217 ?

Guillermo

10-24-2006, 10:15 AM

I've taken some time to study the influence that the downflooding angle (which's info is almost always neglected from manufactures) has in the STIX number, by means of a 'case study': The new Bavaria 37.
I've taken data from PBO magazine, October 2006 issue and worked on the stability curve there (I asume it's drawn for the stated displacement of 6900 kg, probably Mmsc, although this last is not clarified at the article).
Downflooding angle is not stated in the article.
I've also digitalized the profile and estimated the body draught, as well as Hce (6.635 m)and Hlp (0.528 m) heights over and under floatation, respectively.
Armed with those numbers I get:

Downflooding angle ---- STIX --- Dynamic Stability Factor ---Downflooding Factor

85º ----- 31,372 --- 0,873 --- 0,944
90º ----- 33,143 --- 0,920 --- 1,000
95º ----- 34,788 --- 0,960 --- 1,056
100º ---- 36,446 --- 1,002 --- 1,111
105º ---- 37,763 --- 1,024 --- 1,167
110º ---- 39,046 --- 1,045 --- 1,222

So, going from 85º to 115º (extrapolating), the boat happens to come from not even being categorizable under "A" category, to an STIX most probably over 40, what Eliasson understands as a more desirable lower limit to STIX. This brings again some worries to me about the real meaning of STIX alone to categorize the seaworthiness of a boat. It may indicate that a boat with no great seaworthiness at all, could be well brought into the A category just adding up watertight volumes upwards.

As we can see the downflooding angle has a major influence on STIX, but manufactures neglect this information. A pity. And maybe not only a pity, because as we saw some posts ago, there are three angles to be considered to determine which one is the downflooding angle, being not necessarily one of the companionway's corners.

Note: ISO 12217 asks for a minimum AVS of 116,2º (Not very high) for this boat to be categorizable under A category. Her stated AVS is 123º.

And now the 'Old' ratios and parameters for her:

Ballast/Disp Ratio W/Disp = 0,29
Displacement/Length Ratio D/L = 203,23
Sail Area/Disp. Ratio SA/D = 16,67
Hull speed HSPD = 7,61 Kn
Potential Maximum Speed PMS = 8,26 Kn
Velocity Ratio VR = 1,09
Capsize Safety Factor CSF = 2,01 (Slightly over 2)
Motion Comfort Ratio MCR = 24,13
Heft Ratio HF = 0,83 (being values over 1 desirable)
Angle of Vanishing Stability AVS = 115 º (Real: 123º)
Roll Period T = 2,41 Sec (Low for a beam of 3.8 m)
Roll Acceleration Acc = 0,17 G's (0.06 being considered as ideal for ocean-goers)
Stability Index SI = 0,64 (1 to 1.1 being desirable)

Because of this AVS and the minimum one asked for by ISO 12217, it seems like if the AVS of 123º is reached by the added volumes of the deck (most probably). Once again: Adding watertight volumes upwards (generally speaking) with no doubt increases the probability of surviving a capsize, certainly, but should we consider a boat as seaworthy only because of this? Not at all, in my opinion.

It's interesting to reproduce some of David Harding's (PBO tester) statements on this boat:
"...In these far-from-testing conditions (shifty 14 knots) we stablished that the boat would work her way up to about 6.5 knots on the wind provided she was sailed fairly free: trying to point rather than foot saw the speed plummet, despite the totally flat water."
"...the 37's beamy, high-volume hull makes the steering highly sensitive to the angle of heel. We needed about half the lock on the wheel to keep her on track in the gusts...."
"The new 37 does what you expect a Bavaria to do, only more so. She's big and remarkably inexpensive....though only time will tell how the current generation of Bavarias et al stand up to the effects of anno Domini."

Guillermo

10-24-2006, 11:02 AM

..I know, the Formula is just one, but both sources are credible and the first expression (for boats with > 10m) is different:

(7+2.25XLbs) and (8+2.2XLbs)

I don't know what is the right one (probably one was an initial experiment and the other the definitive version and the one in use). I will need sometime to find out the correct one. Perhaps you can check it out for me on the official papers that define Iso 12217 ?
Paulo,
At ISO 12217-2:2002 currently in force it only appears that factor as being 7+2.25*LBS. Probably the other factor, conceived for boats with LBS under 10, was abandoned in the ISO 12217 validation process.

luso

10-24-2006, 01:22 PM

Guilhermo thank you so much for the calculations. Does the AVS mean the angle that the boat can heel and right itself up? What happens if the boat passes that angle? will it remain inverted? If you don't mind me asking also what does capsize safety factor and motion confort mean? I hope I am not picking your brain to much but your knowledge is greatly appreciated. Thank you!

luso

10-24-2006, 02:05 PM

I was reading one of your messages where you mention the size of the sails. We have two equal size masts. (50ft each). The measurements are as followed:one of the booms is 12 1/2ft and the other is 12ft. Both boom tracks go from 48 to 62 inches above deck (we were thinking to raise both boom tracks to 6ft so we can have a clearance under the boom of six feet. Is that a good idea?) We also have a hack on jib that we where thinking about replacing it with a roller furling and on the front inner stay we have a yankee hank on that we are thinking of also replacing it with a furling. Does that change anything regarding stability? Thanks!

Guillermo

10-24-2006, 04:14 PM

Does the AVS mean the angle that the boat can heel and right itself up?
Yes, the limit. But be careful: This estimated AVS may be pretty far away from the real thing. Could even be less. Only with a proper calculation its value may be trustable.
And you have to take into account the downflooding angle. This usually is lower than AVS, and when reached we can no longer talk about intact stability, as we are doing here. Flooding has to be considered into calculations, and that's a more complicated world.
Further on: What gives you a better idea of the ability of a boat to resist a knock down is the amount of area under the GZ (uprighting arms) curve up to 90º, rather than AVS. Or, easier, the value of GZ at 90º. The higher the better. If I were you I'd try to get all this info from the designer, as Vega suggested.

What happens if the boat passes that angle? will it remain inverted?
If the negative part of the area of the GZ curve is big enough, yes, it will have a tendency to remain turtle. If the area is low, waves, or even inertia, probably will right her up in a few moments. To judge all this is why you need a proper GZ curve from the designer or an NA.

...what does capsize safety factor and motion confort mean?
The capsize safety factor was conceived after the Fastnet Race disaster. Is asumed that values under 2 are desirable for ocean going boats, although there is a lot of controversy about the trustableness of this. But it gives a clue. The lower under 2, the better.
Motion comfort ratio was stablished by designer Ted Brewer to give a clue about the quality of the transverse motions of a sailing boat. It serves to compare a boat against other of similar size and type. A better clue to the quality of motions is the natural rolling period of a boat in seconds, T. A value similar to the breath of the boat in meters , even a little big bigger, is desirable. If T is too low, motion becomes uncomfortable, tiring and even risky (This is very important in fishing boats, where you need what is called a good 'platform stability', for the sake of the workers!). T depends greatly on the beam of the ship, so the bigger the more uncomfortable movements, generally speaking (But you cannot make B as low as to threat stability! It's a matter of balance)
You can measure T very easily in your boat: Make her roll freely in calm waters at not very big angles (shifting people from side to side and then stoptping them at the middle, i.e.) and measure 10 complete full rollings, from one side to the other and back, and then divide the total period of time by 10 and you'll get an accurate measurement of the natural rolling period for that particular load condition. Be sure that nothing impedes the boat to roll freely (warps, etc).
Cheers.

Guillermo

10-24-2006, 04:17 PM

...we were thinking to raise both boom tracks to 6ft so we can have a clearance under the boom of six feet. Is that a good idea?... We also have a hack on jib that we where thinking about replacing it with a roller furling and on the front inner stay we have a yankee hank on that we are thinking of also replacing it with a furling. Does that change anything regarding stability? Thanks!
Generally speaking increasing weights aloft affect negatively the stability, but to judge what you mention, the curves are needed once again!

luso

10-24-2006, 08:39 PM

Guilhermo,
This is the reply a got from Carof:
-------------------------
Dear Ms or Mr (?)

I am very sorry, but Lex Eterna was designed in 1973... more than 33 years... And I have not the values you asked for. In France Lex is approved for 1st category : without any limit (not limited)... No problem for the vanishing angle, here that is never asked for such a boat !!!

Her weight is excessive! 23T is too much!

The weight empty is about 15T, and the displacement maxi is about 19T.

Maxi 20T...

Sorry,

"Cordiales salutations" G caroff
---------------------------
Not much unfortunately....
This issue of not knowing the stability really bothers me. When we bought the boat it was empty inside just the bare hull so I measured everything including the caverns and the thickness of the metal hull. I also have the weight every thing that is going in the boat. Would all those measurements and number help in finding the curve? You have helped me alot already, I feel a bit embarraced asking all these questions, but these are some of the things I would like to know and I have tried to find out but to no avail. Could I hire your services?

Guillermo

10-25-2006, 12:19 AM

luso,
I've sent you a private message.
Cheers.

Vega

10-25-2006, 07:39 PM

Paulo,
From my point of view (I've stated this before), comfort is an important component of seaworthiness for cruising boats. A tired crew may come into dangerous situations, and we are talking here about the RCD, which is intended for the recreational market, not the racing one.
A proper globetrotter cruiser under category "A", should look after her crew, in my opinion, being the quality of motion (comfort) an important issue. .

Yes, and I was saying that I disagree. I mean you can obviously have your own opinion in what regards a boat for your own use but I don't think you should generalize.

Or putting that disagreement in the words of another member:

Fast boats are not dangerous boats, neither are slow boats safe boast, if you get my drift, but fast boasts get you there, why wallow around like a drunk pig, when you can sail there?

What sailors call comfort varies widely. What is comfortable to you can be just boring and devoid of any sailing pleasure to a sportier cruising sailor, and I am not talking of racing, but in making an Atlantic crossing in 15 days instead of 23.

So, I guess that regarding safety, STIX is a good indicator, and the comfort you need is a very personal thing, and varies as much as the different kind of cruising boats that are suitable to do Ocean passages, from the very heavy boats with small rigs that you favor to the very fast cruising racers.

Regarding STIX I have shown that some cruiser-racers have a superior STIX number than some boats that are regarded as more suitable to cruising. Things are not always what they seem.

I guess that I would chose one in between those two, but it is just my personal choice and I would not disapprove of any other choice, providing that the boat has the seaworthiness that it is needed and suits the sailors that will crew it ( the comfort and pleasure of sailing).

I'd appreciate very much if you could provide me with the stability curves of the boats you listed in your last post (Do those curves indicate downflooding angle?). Do you have them? Could I get them from you? The rest of info needed to perform a full approximated STIX calculation for those boats.

Sorry for the delay in answering.

I don’t know if I can have the stability curves of some of those boats, because if I will have them, they will not come from the internet and I will have to search.

Modern well designed boats (as almost all big production sailing boats) have a relatively high downflooding angle (more than 100º).

I will try to help you, but I don’t understand why you want to perform an approximate STIX calculation for those boats, if I have given you the exact STIX number, according to ISO 12217.

I will post a curious comparison of several GH and RM curves and STIX numbers of several very different sailboats, among them a very fast ocean cruiser racer (IMS WASA 41) with a high STIX number. I hope it helps, if not, please tell me what you want exactly and I will see what I can find.

Regarding the Bavaria 37, I agree that intact stability is very important, as well as the downflooding angle.

I don’t know what the downflooding angle of the Bavaria 37 is, but judging by similar boats I would say that it is more than 100º. Probably, between 105º and 115º. But you provide a STIX of 39 for a 110º downflooding. I don’t believe it. I don’t think that boat has a Stix superior to 34, probably even lower.

It's interesting to reproduce some of David Harding's (PBO tester) statements on this boat:

……."The new 37 does what you expect a Bavaria to do, only more so. She's big and remarkably inexpensive....though only time will tell how the current generation of Bavarias et al stand up to the effects of anno Domini."

About this, there is no doubt; Bavaria has become the biggest boat manufacturer:p .

Regards

Vega

10-26-2006, 07:13 PM

About “Things (that) are not always what they seem”:

For example, normally the most common opinion is that older and heavier boats were always safer and more seaworthy boats, with better overall stability, if compared with newer models.

Let’s look at the Swan 44 MK2 (1996), an actualization of the MK1 (1989) designed by Frers 17 years ago.

Swan 44 -Displacement 11 T; STIX 38

And to the Swan 45, also a Frers boat but a 2002 Design:

Swan 45 – Displacement 8.9T; STIX 57

Another example : older, heavier and narrow boats are always more seaworthy than lighter, modern and beamier boats (and I chose as an example of the heavier boat one that is renowned by its seaworthiness, the Contessa 32).

Contessa 32 – Displacement 4.3T Beam 2.9m STIX 33

Elan 31 - Displacement 3.8T Beam 3.2 STIX 34

Etap 32 -Displacement 3.9T Beam 3.4 STIX 36

Finally it is good to see that some boats are what they seem. Let’s look at some examples of boats not bigger than 40ft, that will pass with flying colors the STIX 40 barrier:

Regina 38 STIX 46; Najad 38 STIX 43; Malo 49.6; Southerly 110 STIX 55; Island Packet 380 STIX 55 ; Fisher 37 STIX 43 ; SEAQUEST PRIMA 38 STIX 52.

You can have your pick, taking into account your sailing style and the comfort you need. Or, looking the other way around, the amount of comfort that you will be willing to trade for speed and sail pleasure.

Here you have boats for all tastes, the ones that Guillermo likes, slow, heavy and very comfortable, like the Fisher 37 or the Island Packet 380, or the middle weights that I prefer, that go from the heavier Regina to the lighter Malo (that one would be my pick) to an Extreme cruiser racer, the Prima 38, not clearly for my age….but if I were 25 years younger, I would be very tempted to cruise and race with that boat. ;)

Vega

10-26-2006, 07:23 PM

Guillermo I have been preparing a reference STIX list, but it is a never ending thing, so I will post it incomplete and I will add more data when I have time to search. If someone posts more data I will post it here as well. This will permit us to have an alphabetical data bank on STIX and AVS (all data is according with ISO 12217).

Cheers

BENETEAU 50 AVS 109 STIX 41

BAVARIA 42 STIX 36

BENETEAU 50 STIX 41

BENETEAU 57 STIX 53

CATALINA 34 MK11 STIX 36

CATALINA 42 40 AVS 105

COMET 36 STIX 32.5 AVS 127

CONTESSA 32 STIX 33 AVS 155

CYCLADES 39 STIX 38 AVS 126

CYCLADES 43 STIX 36 AVS 121

DISCOVERY 55 STIX 37 AVS 122

ELAN 37 STIX 40 AVS 136

ELAN 40 STIX 37 AVS 128

ELAN 44 STIX AVS 124

ETAP 32 STIX 36 AVS 122

ETAP 34 STIX 37 AVS 123

ETAP 37 STIX 42 AVS 123

FIRST 36.7 STIX 34 AVS 126

FIRST 40.7 STIX 37 AVS 126

FIRST 42.7 STIX 35 AVS 118

FIRST 44.7 STIX 41 AVS 130

FIRST 47.7 STIX 46 AVS 123

FISHER 34 STIX 33 AVS 180

FISHER 37 STIX 43 AVS 180

HANSE 371 STIX 35 AVS 122

HANSE 411 STIX 33 AVS 128

HANSE 461 STIX 35

HANSE 531 STIX 39

HARLEY REFLEX 38 STIX 41 AVS 143

HOD 35 STIX 41 AVS 140

HUNTER CHANNEL 31 (single keel) STIX 32 AVS 130

HUNTER CHANNEL 31 (twin keel) STIX 33 AVS 130

HUNTER CHANNEL 323 STIX 35 AVS 149

ISLAND PACKET 350 STIX 49 AVS 141

ISLAND PACKET 370 STIX 43

ISLAND PACKET 380 STIX 55 AVS 136

ISLAND PACKET 420 STIX 59 AVS 136

ISLAND PACKET 440 STIX 48 AVS 133

ISLAND PACKET 445 STIX 53 AVS 141

ISLAND PACKET 485 STIX 66 AVS 143

J12O STIX 43 AVS 127

J100 STIX 37 AVS 126

J125 STIX 42 AVS 131

J133 STIX 46 AVS 130

J145 STIX 52 AVS 139

J160 STIX 57 AVS 118

J42 STIX 45

J46 STIX 48 AVS 127

MALO 45 STIX 62

MISTERY 35 STIX 32 AVS 156

NAJAD 380 STIX 43 AVS 128

OCEANIS 343 STIX 34 AVS 134

OCEANIS 351 STIX 35 AVS 125

OCEANIS 361 STIX 32 AVS 120

OCEANIS 36CC STIX 35 AVS 126

OCEANIS 373 STIX 36 AVS 132

OCEANIS 381 STIX 38 AVS 130

OCEANIS 393 STIX 43

OCEANIS 411 STIX 37 AVS 114

OCEANIS 423 STIX 38 AVS 119

OCEANIS 44CC STIX 34 AVS 110

OCEANIS 461 STIX 37 AVS 115

OCEANIS 473 STIX 48 AVS 119

OCEANIS 523 STIX 46 AVS 111

OCEANIS 42CC STIX 38 AVS 38

SEAQUEST 32 STIX 37 AVS 132

SEAQUEST 36 STIX 46 AVS 142

SEAQUEST PRIMA 38 STIX 52 AVS 131

SOUTHERLY 110 STIX 55 AVS 151

SOUTHERLY 115 STIX 51 AVS 150

SOUTHERLY 35RS STIX 37 AVS 160

SOUTHERLY 135 STIX 54 AVS 139

SUN ODYSSEY 37 STIX 33

SUN ODYSSEY 39i STIX 33

SUN ODYSSEY 40DS STIX 37/39

SUN ODYSSEY 40.3 STIX 36/38

SUN ODYSSEY 43/43DS STIX 44

SUN ODYSSEY 52.2 STIX 50

SUNFAST 35 STIX 33 AVS 127

SUNFAST 37 STIX 32

SWAN 40 STIX 36 AVS 112

SWAN 44 STIX 38 AVS 123

SWAN 45 STIX 57 AVS 134

SWAN 46 STIX 53 AVS 128

SWAN 48 CR/R STIX 49 AVS 135

SWAN 56 R STIX 50 AVS 127

SWAN 56 R/C STIX 55 AVS 124

SWAN 57 RS STIX 53 AVS 132

SWAN 60 R STIX 68 AVS 128

SWAN 60 R/C STIX 70 AVS 122

SWAN 601 STIX 84 AVS 153

SWAN 62 STIX 63 AVS 122

SWAN 68 R STIX 76 AVS 127

SWAN 70 STIX 82 AVS 133

SWAN 75 R STIX 81 AVS 121

SWAN 80 R STIX 80 AVS 138

SWAN 82 R STIX 88 AVS 127

VANCOUVER 28 STIX 36 AVS 170

VANCOUVER 34P STIX 35 AVS 166

VANCOUVER 34C STIX 36 AVS 139

WARRIOR 40 STIX 47 AVS 133

WESTERLY OCEAN 43 STIX 40 AVS 129

X YACHTS 37 STIX 35 AVS 123

X YACHTS 40 STIX 37 AVS 113

X YACHTS IMX 40 STIX 47 AVS 132

X YACHTS 43 STIX 40 AVS 119

X YACHT IMX 45 STIX 46 AVS 124

X YACHT 46 STIX 44 AVS 123

X YACHT 562 STIX 57 AVS 122

X YACHT 612 STIX 51 AVS 110

X YACHT 70 STIX 73 AVS 126

X YACHT 73 STIX 84 AVS 121

Guillermo

10-28-2006, 03:06 AM

Excellent posts Paulo, thanks!

As I'm interested in more deeply analize STIX through its numbers and its implications, I think we could focuse on a couple of boats (to compare them, precisely because things may not be what they seem), for which we could get as many detailed info as possible.

Maybe we could use those Swan boats you mention: 44 MK2 and 45 . Do you have detailed info on them, including GZ curves?

Also very interesting should be to compare the old 44 from Sparkman & Stephens with the 44 Mk2 from Frers.

I have begun to gather info on those boats, but unluckily the info, even at Nautors' pages is not good enough. I'm going to digitalize images from Nautor's pages and convert them to CAD (I'll do that at the office, next Monday), to be able to get some of the needed (but not publicised) measurements as accurately as possible.

If you do not have GZ curves for those models (44, 44 MK & 45) we may try to get them from Nautor, for the Mmsc load condition.

By the way: I've never stated I favour very heavy under-rigged boats. Maybe my posts caused you that misunderstanding, but I never said that. What I've stated (And still maintain) is that in my opinion heavier boats are generally speaking more inherently safe for all around short handed ocean cruising than light boats. Even STIX favour higher displacements to this end, its value influencing FDL, FBD, FKR, FIR and FWM factors (wow!), as has been already seen in previous posts in this thread and can easily be screened for in the "Determination of Monohull Stability Index (STIX)" page from Eliasson I've posted also here.

P.S.:
Being LBS =(Lb+2Lwl)/3 , we get, for the Swan 45 a 12,657 figure and, for the 44 MKII, 11,507. That's quite a difference, greatly influencing the STIX calculation, which's factors just correct up and down the 7+2,25*LBS figure, what we may call the 'basic' STIX number for a boat.

The Swan 45 has only 43 cm more in Lh than the 44 MK II, but much more Lwl (12,07 m vs. 10,56 m). We can see here the great advantage STIX gives to bigger flotation lengths against hull lengths, favouring plumb bows against longer overhangs (I think this is one of the reasons for this trend in many modern designs). As I've stated before, boats may be not safer because of this, but in fact less, one of my concerns.

More: In this Swans' case, the 7+2,25*LBS values are 35,48 for the 45 and 32,89 for the MK II. If we compare the STIX value posted by Vega for the MK II, we find the several Factors correcting the 'basic' STIX make for an increase of 15,5% (coming from 32,89 to 38). This effect alone would bring the 45's "basic" STIX of 35,48 up to 40,99. And, if we add the effect of, let's say a 5º increase in Dfl (let's do this just for the sake of discussion), just adding some freeboard or deck volume, we can get a further 3% increase (As we found it happenes with the Bavaria 37, when we increase Dfl from 105º to 110º). We can get, just because of these two effects combined, an STIX of 42,3 which is already bigger then the 38 figure for the 44 MK II (It is still far away from the stated 57 value, you may say, and you'd be right, so that's why we must find where the differences are and why).

But, even not being these effects (If they are at all) the main cause for these Swans' STIX difference, through this exercise we can realize again how just using a higher Lwl/Lh ratio combined with a higher Dfl angle (this last being maybe only a matter of not watertight openings positions on deck, or also bigger deck volumes, not hull changes) can lead to very significative variations in STIX. So it may easily happen, or at least we can suspect this, that a boat with a higher STIX number than other it is not inherently more seaworthy than the one with lower STIX (As I said before, a higher Dfl is safer than a lower one from the point of view of downflooding, for sure, but this only doesn't make a boat more seaworthy: A too high freeboard also rises weights and increases windage, i.e. All of us know many boats around there with high topsides which do not stand up precisely because of their seaworthiness....)

P.P.S.: I would like to encourage other people (especially designers) to share their info and opinions on these matters with us (This is becoming a Vega-Guillermo conversation only, which is not rich enough).

fcfc

10-29-2006, 03:12 AM

In this paper, http://www.oossanen.nl/pubs/VOA_MY_CEM.pdf chapter 4.2 and 6.3 contain some info about stix and stability. But that's not my cup of tea.

Guillermo

10-29-2006, 04:03 AM

fcfc,
Already knew it, but thanks a lot anyhow. It's a very interesting paper about a very interesting program for parametric first stages of design estimative. Probably it will become a powerful tool in the future, although for the time being it seem to serve only for a certain style of boats (finned bulbed keels, masthead rigs and single skin fiberglass)
Cheers

Vega

10-29-2006, 12:23 PM

Hello Fcfc,

Nice paper, but about a program for sailboat design: “The CEM as presented here, is a first small step, on the way to a powerful tool in sailing yacht design”.

STIX has nothing to do with Yacht design, quite the opposite: it is an evaluation for an existing Yacht about its stability and seaworthiness. It is intended not for professional, but for the common user, just to give him a correct idea of the seaworthiness of a given boat.

It is in that sense that RYA says that: “just the same way it is mandatory for the fuel consumption of all new cars to be published…that stability information should also be available to a buyer of a boat”.

STIX is only an easily understandable index (but found through a complicated calculation that takes into account a lot of different stability factors) that is, in the RYA opinion (and mine), the most sophisticated stability screening tool available.

Certainly very superior to the old ones, that in many cases were very misleading and were not unified. I mean, you needed to take a look at several to have an idea of the boat, and many times a wrong idea, mainly with modern deep drafted bulbed yachts.

Don’t get me wrong, it is not a perfect tool, (only the best until now).

Personally I take a look at the STIX for having a general idea, but my evaluation is done independently by the analysis of the RM curve and done by a close examination of the boat (and I mean not a virtual one), with answers about the way it is built and the kind of materials that are used. Special incidence in the way the keel is fixed to the boat, about the rudder and about the hatches and all the “glass” surfaces and the way they are secured to the boat. Not that these are the only important points, but if special care is taken with these ones, there is a good possibility that all the others are well taken care of.

But for understanding a RM curve correctly you have to know a lot more.

STIX is just a number and its interpretation could not be simpler: The bigger, the better.:p

…………………………………………………………………………………………..

Thanks Guillermo:) ,

I agree with you in what concerns the misleading importance of the LOA and LWL of the two Swan boats, regarding STIX. Not on what concerns higher freeboard, regarding the 45, compared with the 44. The 45 is a cruiser-racer, a winner in many oceanic races, and a boat with low freeboard.

For what you want, I think the best will be a comparison between the Swan 45 and the 46, both very recent boats, but also very different ones: one a racer, with some cruising in mind, the other a pure cruising boat.

I have my proper suspicions about the way STIX can mislead, when comparing very different boats, but I don’t want to influence you. We can see about that when you perform that comparison.

What do you think of the two boats that I think will fit your criteria to this comparison?

The racer has a higher STIX(57) and the cruiser a lower one (53) and it is a much heavier boat.

I think that I have the GZ (or RM curve) of both boats.

Guillermo

10-29-2006, 02:54 PM

Paulo,
those two boats may serve. I'd appreciate if you provide the data you have for them.
Also I would like to study boats with their STIX between 32 and 40. if you have data for such boats from your list, it would be a great help.

About the STIX not being used in the design stage, I'm afraid it's not like that. You produce a rule and inmediately all designers will try to stretch it as fully as possible. As a matter of fact, what I'm interested in, is analizing the ways STIX can be stretched to produce boats fulfilling the different categories requirements, being the 'A' the most significative, as well as finding the incongruencies and weaknesses that, as any other human system, it has.

From a marketing point of view, I don't see a boats' manufacturer telling to potential buyers: "don't worry, the boat is 'B' categorized, but having a STIX of 31, it's almost an 'A' one". Probably his designer will do the trick and make that boat go into A category, from the very beginning. Don't you think so?

If you read carefully the CEM (which is a designing tool) paper (see at the end of point 4.2 there), you'll realize it estimates the STIX number, among many other things, as it is an important data right from the very early stages of design.

Cheers.

Vega

10-29-2006, 04:27 PM

Also I would like to study boats with their STIX between 32 and 40. if you have data for such boats from your list, it would be a great help.

About the STIX not being used in the design stage, I'm afraid it's not like that. You produce a rule and inmediately all designers will try to stretch it as fully as possible. As a matter of fact, what I'm interested in, is in analizing the ways STIX can be stretched to produce boats fullfilling the different categories requirements, being the 'A' the most significative, as well as finding the incongruencies and weaknesses that, as any other human system, it has.

From a marketing point of view, I don't see a boats' manufacturer telling to potential buyers: "don't worry, the boat is 'B' categorized, but having a STIX of 31, it's almost an 'A' one". Probably his designer will do the trick and make that boat go into A category, from the very beginning. Don't you think so?
.

That's not a problem to find data on boats with the stix between 32 and 40, and of course, you are right, for having a boat classified in class A I believe that some designers use some tricks.

But as a marketing and information tool, the STIX is a failure (till know). I mean the average consumer doesn’t even know what it is and almost nobody in the boat industry uses the STIX to advertise the qualities of their boats. Fact is that nobody, except Malo and Southerly gives that information on their catalogs.

It’s a shame, but to the manufacturers, STIX is only important to get their boats classified as Class A and as the requirements for that are very low, it is only on boats with less than 36ft that they have to “control” it on the design process.

For what you want (information about those tricks) I would suggest that you got information on the new OVNI 345. All OVNIs, except this one, are designed by Philip Briand; this one is designed by Joubert-Nivelt and I have heard that one of the reasons is the “need” of having this boat approved as Class A.

I don’t have the data on that boat, but if you ask that to the Alubat Spanish importers (Argonautica), they will get it for you (it will depend on the way you ask:P ).

Info@argonautica.es

I will see what information I have on boats that are classified as Class A and obviously are close to the limit (light 34ft with low AVS and a big negative stability).;)

cheers

fcfc

10-30-2006, 04:54 AM

P.P.S.: I would like to encourage other people (especially designers) to share their info and opinions on these matters with us (This is becoming a Vega-Guillermo conversation only, which is not rich enough).

Although ISO 12217 is an international rule, I think it is mandatory only in Europe (Recreational Craft Directive for CE mark). US, australian or new zealand boaters have either no rules, or their own sets of rules.

On ABS rules, the only rule dealing with under 80 ft boats is ORY-37, which only deal with sailboat structure. Nothing for stability, nothing for small powerboats.

Guillermo

10-31-2006, 01:19 AM

Paulo has posted a new thread on the interesting new Class 40. See http://www.boatdesign.net/forums/showthread.php?p=112261#post112261

I bring that to here because I think it's a nice example of what shall not be done with the RCD. Saying those boats are capable for family cruising is out of the limits of the RCD. Those boats are clearly conceived for racing and this is out of the scope of the Directive.

Taken from http://www.class40racing.com/index2.html :
"Owen Clarke Design also claim of their long coachroof design: "Designed for true offshore competitive performance but also as a dual role yacht in which the family can take off cruising, rolling off fast effortless miles to those holiday destinations. The characteristics of a solo race boat will make her a reliable and steady short handed fast cruiserwith the foot released a little of the accelerator and a cold beer released from the ice box!""

Taken from http://www.class40.com/index.php?section=14
"The safety of the boat and its crew is the inalienable responsibility of the sole owner, or its skipper, which must ensure that the yacht is in a good condition all over, perfectly seaworthy, and that it is manoeuvred by an experienced crew, which has taken the appropriate training and is physically capable of confronting the bad weather."

This is getting absolutely eschizofrenic!

From a technical point of view, it's interesting to note that under Class 40 rules is mandatory to fulfill requirements of ISO 12217:2002 for A category, but, on top of that, they demand the passing of a 90º test:

"This test is aimed at proving that the boat is capable of righting itself from the broached position in it’s least favourable ballast configuration....
When heeled at 90 degrees the loaded boat is kept in this position with the aid of a strop passed around the mast at the level of the band at the top point of the mast. The tension exerted on the strop must not be lower than 220 kg."

Ability to recover from a knockdown is considered at the STIX by means of the Knock Down Recovery Factor FKR. So it seems there is a redundancy here. Do these Class 40 guys think STIX is not good enough...?

I would like to bring here again one my first posts in this thread. I stated there some thoughts from Rolf Eliasson:

"But it has to be noted that, since STIX gives no consideration to the importance of the negative areas, it is fully possible to draw a boat that's wide and flat with a low center of gravity, with a GZ curve that reaches to the sky quickly, and then drops again as quickly as it rised, just passing the minimum Avs requirement, and producing a negative area almost as big as the positive one. Such a boat could still receive a category A rating, which it clearly does not merit; it would be unsafe in the conditions outlined in that category."

"...It's always possible to add more factors (To the STIX) without disturbing the end result, which should hover around a factor of 1. I'm thinking of Stability Loss due to Speed Factor, Transverse Inertia Factor, and GZ-area Ratio Factor (positive vs. negative areas), among others...."

Crag Cay

10-31-2006, 05:41 AM

I'm sorry Guillermo, but I fail to understand any of your implied criticisms of this class. It seems to me to be one of the more carefully considered classes and one I welcome whole heatedly. I can find very little in either their ethos or detail that is less than commendable.

The class requirement to comply with the various ISO regs is a neat way of controlling various parameters at the design stage. But as you say, these are racing boats and therefore RCD compliance is not legally required, so involvement of the Notified Bodies and their cost, can be avoided. However, the class has instigated a series of measurement tests to check class rule compliance, OSR Regs and by inference, ISO compliance when combined with data from the designers. This includes weighing each boat and performing the 90 degree recovery test, that was developed, and has proved effective with the Open Classes. In this instant it is performed in the least stable configuration, ie with 750kgs of water ballast in its least favourable position.

Wide beam and flat decks are recognised as a problem and hence there is a deck and coach house volume requirement (above the sheer plane) in the rules to try and minimise this.

Some of these boats are promoted as cruiser /racers, and some will go into series production. This will obviously have an impact on the process they have to go through with regard to RCD compliance before they are brought to market.

But after that, people are free to do with their boats whatever they like. When I campaigned an IOR 2 tonner, it took 14 crew to race it competitively under IOR, but I raced it happily double handed and enjoyed miles of cruising either alone or with attractive, but nautically clueless young ladies. And that was before self tailing winches, ATN snuffers and roller furling to help.

We must be very careful to never promote the RCD as having any relevance to what people are free to do with their boats. If this already happens in Spain, then I am sorry. But encouraging its spread to the rest of the free world is an insidious undermining of everything we hold dear. There are enough faceless bureaucrats who would love to do this without sailors giving them any encouragement.

I think you are too willing to promote your own boating preferences as being 'the best way for everyone to do it'. I would never criticise your choice of cruiser as you clearly enjoy sailing this way, but please allow others to make their own decisions. In the same way, I've heard there are people who actually make love with the lights on. Crazy, wild and reckless behaviour in my eyes, but it's their choice.

Vega

10-31-2006, 06:02 AM

Paulo has posted a new thread on the interesting new Class 40. See http://www.boatdesign.net/forums/showthread.php?p=112261#post112261

I bring that to here because I think it's a nice example of what shall not be done with the RCD. Saying those boats are capable for family cruising is out of the limits of the RCD. Those boats are clearly conceived for racing and this is out of the scope of the Directive.

Taken from http://www.class40racing.com/index2.html :"Owen Clarke Design also claim of their long coachroof design: "Designed for true offshore competitive performance but also as a dual role yacht in which the family can take off cruising, rolling off fast effortless miles to those holiday destinations. The characteristics of a solo race boat will make her a reliable and steady short handed fast cruiserwith the foot released a little of the accelerator and a cold beer released from the ice box!""

.....

Ability to recover from a knockdown is considered at the STIX by means of the Knock Down Recovery Factor FKR. So it seems there is a redundancy here. Do these Class 40 guys think STIX is not good enough...?

..."

About the STIX, they (as many people) obviously don’t consider enough the requirements needed for certifying a boat in Class A. Their own requirements are more demanding.

About the rest, I disagree with you and I agree with Owen Clarke.

Of course, I am too old and to "spoiled" with comfortable things to personally want one of those as a cruising boat.

I agree that the boat will not be comfortable in a seaway, but in what regards stability and safety and scantlings, the boat will be very safe and hard to capsize. I mean it will be a very difficult boat to break under normal circumstances, because it is designed for bigger rigs and extreme situations, and his huge positive stability will make it a very stiff boat.

Of course, even if not likely, all boats can be capsized and the problem here as to do with inverted stability, that in these (beamy) boats can be a problem. But if the AVS of the boat is around or bigger than 120º (and the inverted stability in accordance with that, as it normally is) I don’t see any problem, except comfort, but that is a personal thing.

Guillermo, this are not racing boats that are proposed for cruising (the 40class is not an open class), but very fast cruiser racers that become racing boats. Several of these boats pre-exist the 40 class as small production boats, and as such, have been already aproved for cruising (class A) in the scope of the Directive.

cheers

Vega

10-31-2006, 06:27 AM

We must be very careful to never promote the RCD as having any relevance to what people are free to do with their boats. If this already happens in Spain, then I am sorry. But encouraging its spread to the rest of the free world is an insidious undermining of everything we hold dear. There are enough faceless bureaucrats who would love to do this without sailors giving them any encouragement.

I agree with you about the rest, but here I think you don't understand my concern (I don’t know about Guillermo) about RCD and "the rest of the free world".

RCD as nothing to do with what people want to do with their boats (as you have stated before) but has to do with the right that the consumer has to have available information on the boat that they are buying, on something as important as stability and seaworthiness.

Crag Cay

10-31-2006, 07:00 AM

I agree, that information should be available, and so should the advice from various sources as to what that information means and the consequences and implications of that information.

But then the consumer should be left to make THEIR choice about the boat they buy and the use to which they put it. If people choose to prioritise speed, excitement and fun over comfort, stability and safety, so be it. It's a free world.

However, I think these Class 40 actually do offer speed, excitement, stability, safety, and fun which only leaves comfort to be debated. Well, that's too subjective, and despite Ted Brewer's efforts at producing a empirical 'factor', I think any realistic one should incorporate the skipper and crew's age, their expectation, wealth and length of time spent at an English Boarding School as a child. This should then be added to 'Bill Tilman Factor' (or monastic quotient in catholic countries) to get a more accurate assessment. Then you will have a realistic explaination of why Robin Knox Johnson is still happy in an Open 60 at 67 years old.

Vega

10-31-2006, 07:48 AM

I agree, that information should be available, and so should the advice from various sources as to what that information means and the consequences and implications of that information.

But then the consumer should be left to make THEIR choice about the boat they buy and the use to which they put it. If people choose to prioritise speed, excitement and fun over comfort, stability and safety, so be it. It's a free world.

... which only leaves comfort to be debated. Well, that's too subjective, and despite Ted Brewer's efforts at producing a empirical 'factor',.

Yes, I agree, but what we are doing in this thread is debating "what that information means and the consequences and implications of that information". And you are very welcomed to this discussion. :p

About Ted Brewer "Comfort Ratio" let me remind you that he also says about it:

“COMFORT RATIO (CR): ...does provide a reasonable comparison between yachts of similar type. ...The intention is to provide a means to compare the motion comfort of vessels of similar type and size, not to compare that of a Lightning class sloop with that of a husky 50 foot ketch.

...Do consider, though, that a sailing yacht heeled ... will have a much steadier motion than one bobbing up and down ..

Nor will one human stomach keep down what another stomach will handle with relish, or with mustard and pickles for that matter!

It is all relative.”

The bold marks are mine.

Cheers

Guillermo

10-31-2006, 09:07 AM

Crag,
I'm not criticising at all the Class 40 boats. Neither any other boat. As matter of fact I like very much the Class 40 concept and the boats that have been designed to it. For their intended use.

I'm sorry if I have not been clear enough in stating my position. Let me try to explain myself again:

What concerns me is this STIX think crawling subtly into the market as being the 'word of God' concerning seaworthiness of boats. Most users have not enough knowledge to properly understand the implication of ISO rules and, particularly, STIX. And, as I'm trying to expose trough my posts in this thread, STIX has its drawbacks, having (in my humble opinion) been influenced in its development, by mass boats manufactures (and even designers!) because of marketing concerns.

RCD is conceived to give all recreational boats customers some kind of protection by means of providing trustable and harmonized information when they buy a boat. So when somebody without deep knowledge buys an A categorized boat, may be expecting (In my opinion) to be able to go anywhere with that boat. Of course RCD state this approach is not valid, but, who knows out there the RCD?

Categorization under the RCD not only depends on stability issues, but on a lot of other matters, as you know. But stability is the highlight of all of them in my opinion. As a matter of fact in Spain all boats under 12 m for categories C and D may be compliance certified by the own manufacturer, except what concerns to stability, freeboard and floatation, where the intervention of a Notified Body is mandatory, if the manufacturer wants the boat to be allowed to sail in waters other than harbours and the like. That's why I'm focusing this thread on stability matters.

I want to impose nobody my way of thinking. I'm just trying to defend the idea that STIX has yet to be more deeply studied and developed, to better indicate the seaworthiness of a boat. Also the necessity of providing extra info for customers, maybe even creating an extra category, or an special warning note, for racers going into cruising mode (As the Class 40s) and cruisers-racers. And at last, but not least, the necessity of all manufacures providing enough and clear information on all this matters in their marketing material.

Cheers.

Crag Cay

10-31-2006, 09:53 AM

Hi Guillermo, I'm afraid there is a philosophical difference between us in our expectation of the RCD. It is a piece of legislation that was never intended to increase safety, was never intended to produce better boats and was certainly never intended to help the consumer. It is and always was a 'free-trade' agreement to level the playing field for manufactures. In the UK its implementation is handled by 'trading standards' officers, to ensure that boats that comply with the Directive can be freely marketed in any of the EEA countries without let or hindrance. And in that, it has met its function. There is now no need to build boats with variations to meets the individual regulations in Italy, Spain or France, as there is common agreement as to a minimum requirement to please everyone.

And I believe there is significance in the notion of a 'minimum standard' and the fact the RCD's function is to benefit the free trade by manufactures, and no one else. Therefore it's entirely right that the big manufactures should campaign to get a market place established that is most advantageous to their trading position. That is what they did and most are happy with the resultant level playing field.

Now if the RCD is being corrupted by either government agencies to regulate boat use, or by the manufacturer's to help sales promotions, then that should be stamped on. We must never deviate from either 'caveat emptor' in the buying process or the skipper's total and absolute final responsibility for the safety of his vessel and crew. This is only possible by education, education and education and not regulation. Stability only forms one small part of the total system that results in safety at sea. A skipper that is capable of understanding everything else that will influence his safety during ocean sailing will be quite capable of understanding the notion of STIX. If through this knowledge he feels he would prefer one boat over another, then that's for him to decide. The idea that Michael Ritchey sailing Jester (Cat B) is less safe than some 'numpty' sailing a 'cruising boat' that just happens to have letter A on a brass plaque, is frankly ludicrous.

So, if people are basing their entire ocean going yacht buying decision on whether it has an A categorisation, then we should let Darwin's theories take their course. The human race will be better without these people in the gene pool.

Guillermo

10-31-2006, 10:46 AM

...It is a piece of legislation that was was never intended to produce better boats and was certainly never intended to help the consumer...
Well, Im afraid I do not agree at all with you. Trade has been probably a main conducting reason, I will not discuss that, but safety and consumer protection are among the goals. From the Forewords of the Directive:

"Whereas the removal of technical barriers in the field of recreational craft and their components, to the extent that they cannot be removed by mutual recognition of equivalence among all the Member States, should follow the new approach set out in the Council resolution of 7 May 1985 (4) which calls for the definition of essential requirements on safety and other aspects which are important for the general well-being; whereas paragraph 3 of Article 100a provides that, in its proposals, concerning health, safety, environmental protection and consumer protection, the Commission will take as a base a high level of protection....
Whereas, in view of the nature of the risks involved in the use of recreational craft and their components, it is necessary to establish procedures applying to the assessment of compliance with the essential requirements of the Directive....
Whereas it is appropriate that the Member States, as provided for by Article 100a (5) of the Treaty, may take provisional measures to limit or prohibit the placing on the market and the use of recreational craft or constituent products thereof in cases where they present a particular risk to the safety of persons and, where appropriate, domestic animals or property..."

...the skipper's total and absolute final responsibility for the safety of his vessel and crew. This is only possible by education, education and education and not regulation.
Skipper responsibility, of course. Education, of course. But also regulation is necessary, as in any other human activity in our crowded world.

....So, if people are basing their entire ocean going yacht buying decision on whether it has an A categorisation, then we should let Darwin's theories take their course. The human race will be better without these people in the gene pool.
Drastic, but I basically agree. :D

Guillermo

10-31-2006, 11:12 AM

Paulo,
May I have from you the Swans' GZ curves?

Vega

10-31-2006, 04:55 PM

Paulo,
May I have from you the Swans' GZ curves?

Guillermo, you may...when I have the time to search and for scanning them,(they are not in my computer). Sorry but I have had busy days.:(

.. the RCD. It is a piece of legislation that was never intended to increase safety, was never intended to produce better boats and was certainly never intended to help the consumer. It is and always was a 'free-trade' agreement to level the playing field for manufactures.

Hey Crag, I am with Guillermo on this one. Certainly it was intended as a 'free-trade' agreement but also as a way to protect and advise the consumer.

“When placed on the market or put into service, craft must be accompanied by a Declaration of Conformity. This certifies that the vessel meets the Essential Safety Requirements (ESR) contained in the Directive.

A Technical Construction File (TCF) must be produced and maintained by the Manufacturer / Authorized Community Representative. This file has to be kept all the time a particular model is in production and for a minimum of ten years beyond production of last vessel.

The TCF describes how the vessel meets the Essential Safety Requirements”

http://www.ceproof.com/recreational_craft_directive_RCD.htm#esr

These Essential Safety Requirements are “essential” to whom? Obviously, to the safety of the consumer.

RYA that have played a large part in the ISO working group that has drafted the new stability standard index screen known as STIX say :

“Just as it is mandatory for the fuel consumption of all new cars to be published so the RYA believes that stability information should also be available to a buyer of a boat”

and suggest that consumers should ask the manufacturers the stability data before buying a boat and they also say :

"If it’s still not made available then smell a rat".

But I agree with you on one thing: for all practical effects, till this moment, the RCD has only worked as a 'free-trade' agreement and that’s why it has not contributed to better boats.

And I disagree with you that the average sailor has a decent information about STIX or boat stability. Most don’t even know what the STIX index is, but almost everybody knows the Boat categories that are certified by the RCD, and in my opinion those categories are misleading, while the STIX is a very useful tool to screen boat stability.

Regards

Crag Cay

10-31-2006, 05:23 PM

I don't want this to become a spitting match between lawyers, but that Council meeting your quote refers to in May 1985 was specifically addressing the 'free movement of goods'. They agreed that there should be a 'new approach to technical harmonisation and standards' as a way of achieving that open market.

The original scope of the RCD did include several basic safety parameters that have since been extended by amendment to include environmental and other concerns. But there still has been no change in the intended purpose of the Directive, that being the 'free movement of goods'.

My only concern is that we in the industry, mustn't encourage it to become something it is not. I appreciate that you and others, including Rolf Eliasson feel there are some aspects of it which give cause for concern, including a view that the STIX number for Cat A is too low. However, rather than try to meddle with the detail, perhaps we should push for it to become even simpler. This ambition to keep the Directive as simple as possible and non prescriptive was one of the stated objectives in its drafting. So in contrast to raising the limit, I truly believe it should either be lowered or better still, the Categorisations should be eliminated altogether.

In support of a lowering: I think it is unrealistic for the required STIX numbers to eliminate boats with a proven offshore ability. For the (British) Folkboat, Contessa 26 and Virtue to be deemed unsuitable for ocean service is bizarre. Therefore the lower limit should include these boats and the resultant huge range of vessels within Cat A would then trigger in the buyer's mind a realisation that there is more to choosing a boat than a simple letter on a brass plaque.

To go further and eliminate the Categories all together is because they, (and the STIX numbers) are trying to convey too much information in a overly simplistic way. This is a disservice to the consumer as it encourages them to be simplistic in return. The information about the boats should be conveyed by a series of indicators without any direct inference as to their suitability for use. This series of values would portray direct information about strength, stability, comfort, range under power, environment concerns, recyclability, etc, and then the consumer would be free to match the demands of his particular use to a particular boat. Lumping all boats above a certain number as being suitable for some generic use, whilst eliminating others of better pedigree, is a nonsense as some of your examples have shown.

This system would shift the responsibility of deciding to what use a boat should be put, back four square in the lap of the skipper. The present situation is only fuelling the time when a case will appear in court between a ship wreck survivor claiming damages against the manufacturer / Notified Body / EU on the grounds they promised him the boat was suitable.

Guillermo

10-31-2006, 06:43 PM

...To go further and eliminate the Categories all together is because they, (and the STIX numbers) are trying to convey too much information in a overly simplistic way. This is a disservice to the consumer as it encourages them to be simplistic in return. The information about the boats should be conveyed by a series of indicators without any direct inference as to their suitability for use. This series of values would portray direct information about strength, stability, comfort, range under power, environment concerns, recyclability, etc, and then the consumer would be free to match the demands of his particular use to a particular boat. Lumping all boats above a certain number as being suitable for some generic use, whilst eliminating others of better pedigree, is a nonsense as some of your examples have shown.
Now we have something interesting here!

I'm not able to find it now, but I posted somewhere else my idea that STIX could very well be a gathering of factors making little sense when mixed all together to get a final figure. Something like if we multiply, or add, or whatever, the 'Old' ratios to come also to a final and simple figure: would that number serve to categorize a boat's seaworthiness? Absolutely not, in my opinion, as we cannot mix pears with apples.

Should we then provide a kind of 'Old' ratios style information to the user, only that more accurate or adequate than those, as you suggest? But, will those ratios or indicators be understood by the general public without specific formation? Would that bring more safety into the boating comunity? Shall we obligue all boaters to become a kind of NAs? Shall we obligue them to get a qualifying course to teach them how to understand things, pass whatever tests and then licensing them as 'qualified boat buyers'? Aren't we going deeper into regulations this way?

And if we do the contrary, and let all people in this wide world go and behave only by their own mood, and use whatever inadequate boat they want for whatever bizarre adventure, how can we avoid crazy people going to sea and killing not only themselves (which could be nice under the Darwin's laws you mentioned) but other people too? (among those, their rescuers)

Not easy answers here. A simple categorization way seems desirable to me, for the sake of the users and the safety of all, but for sure we can do better than STIX (although I recognize it has been a good first try).

I would love to see you developing further your idea in this forum, with specific and detailed proposals. It would be a very nice matter of discussion.

On my side, and in the mean time, I will keep on working on the STIX number, trying to find out what can be done that way. And I need the help of Vega for this, as he has gathered a lot of info on a lot of boats. ;)

Cheers.

Vega

11-01-2006, 11:32 AM

Robin Knox Johnson is still happy in an Open 60 at 67 years old.

About this, it’s interesting to hear what he says about the seaworthiness of its Open 60, in conditions that Mike Golding (in his six circumnavigation) described as about the most ferocious he has encountered:

"I had a maximum of 70.4 knots five times. It is not often you see 70 knots and I have seen it before but I was going downwind with it. It was horrible and at times genuinely frightening".

Robin Knox Jonhson says about it:

"The waves are watery Himalayas, it is as bad as anything you would see in the Southern Ocean,

The wind sounds like the BBC sound effects for a storm in Antarctica.

Everything around me is white, you dare not look into it as you would be blinded”.

The boat is otherwise fine and just needs the chance to show herself, she has been riding the waves beautifully - an absolute dream. She's really good, it is just a bit uncomfortable for the human inside her. “
.

fcfc

11-01-2006, 01:35 PM

And if we do the contrary, and let all people in this wide world go and behave only by their own mood, and use whatever inadequate boat they want for whatever bizarre adventure, how can we avoid crazy people going to sea and killing not only themselves (which could be nice under the Darwin's laws you mentioned) but other people too? (among those, their rescuers)

I am sorry you cannot do that.

If you want to look how heavily regulated domains behave, just look general (private) aviation. Rules have been put to a "high" level of safety. Due to very high certification costs, it nearly killed the market. An aircraft GPS is around 15 000 euros (garmin 430). So private pilots just fly planes without GPS, and use any handheld GPS. Same for engines. You can still buy a NEW 125 hp, carbureted, magneto ignition aircraft engine for about 30 000 euros. This is possible due to the enormous lack of competition created by huge certification costs.
And people who can no longer afford to be killed in general aviation simply get killed using unregulated flying objects like ultraligths or powered chutes. You do not save any people. You just get them killed somewhere else outside your rule scope.

In the marine use, it will be the same. If you make ISO as stringent as LLOYD unlimited service rules, most people will no longer be able to afford a somewhat reasonable boat to cross atlantic. They will just be drowned using beach toys, pedalos or jetskis to cross atlantic.

Guillermo

11-01-2006, 02:48 PM

In the marine use, it will be the same. If you make ISO as stringent as LLOYD unlimited service rules, most people will no longer be able to afford a somewhat reasonable boat to cross atlantic.
In my opinion this is not quite so. The cost of a full category A certification is not cheap, but it is only an small fraction of the value of the boat, and this talking about a single unit. If we talk about mass production boats the impact of the cost of certification becomes ridiculous.

But we always find people reluctant to pay such services. In my experience, people who don't care to pay 4000 euros for a piece of not vital equipment, many time toys, become very angry to pay the same 4000 euros for a certification. The same kind of reluctancy we can find around about designers' fees.

On the other hand, what we see around are a growing number of pricey boats, instead of the contrary. My experience is that boats here in Galicia are bigger and fancier every year. The widow of the former owner of my boat told me that when they bought the boat from new, back in 1971, it was 'grandious', being 11 m length, whith relatively very few boats around being bigger than that. But with the passing of years the boat (she said in a funny mood) was getting smaller and smaller, to the point of becoming just one more of the crowd.

What amazes me is why there are people who think they have the right to cross an ocean without the proper equipment, but we do not see the same kind of people claiming for that same right to cross the Kalahari, climb the Everest or just go deep diving.

Cheers.

Vega

11-01-2006, 06:41 PM

Finally I was able to find the proper magazines and had time to scan the data on the Swan boats.

I have suggested these two boats to you, because I believe that the Swan46 is a more seaworthy and stable boat than the swan 45 (even if this one is a very seaworthy one).

The GZ curves of both boats are great, among the best in their categories, but the much superior displacement of the Swan 46 will give it a bigger RM curve. And that doesn’t show on the STIX number, being the one from the 45 slightly bigger.

The FDS is calculated using the positive area under the righting arm curve, up to the Avs in this case (as Afl>Avs).

Yes, I think that it should be that way, but apparently it is not. The area considered is not the one under the RM curve, but the one under the GS curve.:(

This way, displacement is not considered and what enters the calculations instead is the Length of the boat. If I am looking at it correctly this will benefit light boats and won’t take into account the role that displacement has in boat’s stability.:mad:

About the GZ curves, the one in French is from the 45.

cheers

Guillermo

11-02-2006, 01:04 AM

Thanks a lot for the curves, Paulo, although I thought we were talking about the 44 and the 45, not 45 and 46. Anyhow I'll work on those and post results with commentaries.

About the FDS thing:
(By the way, I said 'righting arm', so GZ curve. Read my quote again)
As I told before, to calculate some of the STIX factors the stability curves input info are taken from the GZ curve, not the RM one. But then displacement is introduced separately, so the multiplying of this last times righting arm gives the RM. This is done this way to calculate the FKR (knowdown recovery factor) and the Vaw (steady apparent widspeed to heel the vessel to Φd when carrying full sail) necessary to calculate the FWM (wind moment factor).

As you correctly point out, it's surprising the so-called Dynamic Stability factor seems to take not into consideration the righting moments, as dynamic stability is related to the amount of energy available, thus the area under the righting moments curve. But they use only Agz (Area under GZ curve) and LH. As the STIX fathers were knowledgeable people, there is probably a reason for that. Let's follow Eliasson's explanation on FDS:
"The reason for not using the righting-moment curve is that size is already accounted for in LBS. In the FDS, the righting arm curve is better compared to a righting-moment curve, so as not to give too much credit to the larger yacht, which is obviously already done with the LBS, FDL and FBD factors."
I would like to add that Working Group 22 (STIX parent group) analized a list of Category 1 sailing boats models, known for not having had stability problems through their lives, and they developed a limiting RM-Loa data curve, so the symplistic FDS formula probably was derived from there or the like. I attach again Van Oossanen paper from the times of the STIX formulation developing.

Cheers.

Guillermo

11-02-2006, 01:38 AM

At last a designer publicising the whole STIX factors!
http://www.yachtdesign.com.br/01_portugues/noticias/news1.htm
(Look at the bottom of the page)

A couple of interesting category A boats of 30' length or under, worth to analize:

- "Multichine 28" from Roberto Barros (STIX 34,3): http://www.yachtdesign.com.br/02_ingles/plans/mc28/mult28-2sp.html
- "Huzar 30" (STIX as high as 38,7 !): http://www.shock-wave.co.uk/huzar/whychoose2.htm

Vega

11-02-2006, 10:13 AM

Sorry about that. You are right about that quote, but you are not right about the swan 44. I have said that I had data on the Swan 45 and 46, not on the 44, (that’s an older boat; see post 101) and the comparison that I had proposed was between the 45 and the 46, precisely because the 46 is a much heavier boat and surprisingly, has a smaller STIX than the 45.

About those explanations about the FDS, I have my doubts, and if you compare the RM stability curves of the Swan 45 and 46 and compare them with the STIX of those boats, you are going to see what I mean.

About the boats you have posted, the Huzar 30 seems to be a very nice boat, with an Impressive Gz curve. The Multichine is another story. Its GZ curve is average and shows a significant inverted stability and a an AVS of only 117º, that I consider too low for a 30ft.

About the AVS and the size of the boat I consider that the MCA guys have the right policies: Smaller the boat, the bigger should be the AVS (because small boats withstand more risk of capsizing than bigger boats).

Take a look at this MCA “Code of practice” :

Guillermo

11-02-2006, 11:47 AM

The Multichine is another story. Its GZ curve is average and shows a significant inverted stability and a an AVS of only 117º, that I consider too low for a 30ft.
Yes, I agree. That's why probably it would be good, following Eliasson, to introduce a GZ area Ratio Factor measuring the relation among the positive and negative areas.

Guillermo

11-08-2006, 12:20 PM

I have had the opportunity to do some works for "Zara of Arran", a classic sailing boat from boatbuilder (and designer?) William Boag in Largs, Ayrshire, Scotland. William Boag had a boat yard in Largs and between 1955 and 1965 he built 50+ Loch Longs yachts. There are still quite large fleets of these (you may search under Cove Sailing Club on the Clyde) and, strangely, the largest fleet down at Aldburgh in Suffolk (Thanks from here to my scottish friend Colin Whimster, who provided this info on the boatbuilder, as I've found nothing in internet).

Data for "Zara of Arran"

Overall Hull Length = 9 m
Length Waterline = 6,8 m
Flooded Buoyancy (Y/N) = N
Beam Waterline = 2,25 m
Beam = 2,43 m
Total draught = 1,29 m
Body draught = 0,64 m
Displacement MSC = 3943 kg
Displacement Max = 4274 kg
Height of CE above DWL = 3,64 m
Height of CLR below DWL = 0,57 m
Angle of vanishing stability = 152 deg
Downflooding angle = 92 deg
GZ at downflooding angle = 0,556 m
GZ at 90 degrees = 0,564 m
Sail Area = 38,7 sq.m
Area to flooding (Agz) = 31,19 m.deg
Area to AVS = 46,6 m.deg

And now, let's see her ratios and STIX based on those numbers (Measurements have been taken directly from the boat. Displacement, GZ curves and downflooding angle calculated at my office after performing an inclining experiment):

Ratios and parameters:

Length/Beam Ratio L/B = 3,25 (Lwl + Lh)/2*Bmax
Displacement/Length Ratio D/L = 379,13
Sail Area/Disp. Ratio SA/D = 14,93
Power/ Disp. Ratio HP/D = 1,91 HP/ton
Hull speed HSPD = 6,33 Kn
Potential Maximum Speed PMS = 6,72 Kn
Velocity Ratio VR = 1,06
Capsize Safety Factor CSF = 1,51
Motion Comfort Ratio MCR = 37,22
Heft Ratio HF = 1,57
Angle of Vanishing Stability AVS = 150 º (Real: 152º)
Roll Period T = 3,58 Sec
Roll Acceleration Acc = 0,04 G's
Stability Index SI = 1,47 (Tender)
Dellenbaugh Angle DA = 38,53 (Very high)

STIX calculation:

Base Length Factor (LBS) = 7,533
FL = 0,927
Displacement Length Factor (FDL) = 1,035
FB = 1,634
Beam Displacement Factor (FBD) = 1,076
FR 7,893
Knockdown Recovery Factor (FKR) = 1,572
Inversion Recovery Factor (FIR) = 1,240
Dynamic Stability Factor (FDS) = 0,658 (Low because of the Dfl angle. Main cause for the low STIX)
Vaw = 0,000 (Not applicable)
Wind Moment Factor (FWM) = 1,000
Downflooding Factor (FDF) = 1,022
Delta = 0

STIX 28,928

DESIGN CATEGORY B
Wave height max 4 metres
Windspeed max. Force 8

(Note: I am not asuming hatches, portlights, windows, etc., fulfill the requirements of ISO 12216 and 12217 for category A or even B, as they most probably don't. I'm not pretending, either, to say this is a going anywhere boat. This is only an exercise.)

The basic problem to fulfill the A category requirements, from the hull forms point of view, is that the very narrow aft sections and relatively low freeboard of the hull (compared to modern ones) provide relatively little buoyancy when heeled, so the downflooding angle (to the upper corner of the companionway) remains low. If the boat would have somewhat wider sections and an slightly higher freeboard, as to provide a downflooding angle just over 100º, as well as a longer Lwl (shorter overhangs), it would have probably come to an STIX over 32, so fulfilling Category A requirements.

So, in line with Crag Cay's concerns, here we have an example of forms that, although having proved their seaworthiness for decades, are penalized under the STIX (Compare with the Multichine 28 posted before)

P.S.: Interesting to note the great influence on STIX of surviving ability when flooded. If we could provide "Zara of Arran" with means to float when flooded, delta factor would be equal to 5 and so STIX would come up to 33,928 so neatly coming into Category A zone.

Guillermo

11-09-2006, 06:05 PM

Let me quote here some thoughts from a couple of knowledgeable guys about STIX and RCD safety in general:

"...there's a feeling within the industry that there's room for a more demanding 'blue water' design category.
There is little to differentiate between a true water cruiser, built to look after you in a storm, and a 9.7 m (32ft) coastal cruiser which has been numerically engineered to meet the minimum requirements for Design Category A"
(David Greening, David Greening Yachting Design, Ltd, Chichester)

"The requirements of the RCD can be seen as a base-line on which to develop seaworthy boats. It does not completely assess overall seaworthiness. For example it does not consider in detail:
- the strength of the masts, sails or rigging
- the seakindliness of the hull
- the existence, size or reliability of the engine
- the standard to which a boat is equipped or maintained"
(Andrew Blyth)

From my point of view, the seakindliness should not only consider keeping low all six possible accelerations induced by the sea, as to increase comfort of the crew and avoid damage to the equipment, but also, and most important, the damping of rolling movements and the minimizing of broaching tendency, back from the design stage, which are vital for seaworthiness in rough seas.

Andrew Blyth adds one more quality also very important: Weatherliness (Effectiveness sailing to winward)

Additionally, on top of the exigency of a large AVS (More than 130º for preference), Andrew Blyth suggests (for category A) it should be used 1/5 as a maximum value for the GZ area Ratio Factor (Negative/Positive), as well as having a maximum inverted moment less than half of the maximum positive one.

Guillermo

11-10-2006, 05:19 AM

Brought to my attention by Antonio Alcalá, chairman of an Spanish Association of Yacht Ocean Masters, here a link to a very interesting boats data list from the RYA:
http://www.rya.org.uk/NR/rdonlyres/EDBEDFCD-F216-46DA-B4F0-B2D0BBB8C2EE/0/StabilityWebPage8Sep20062.pdf
Several of the boats include their RCD STIX.
Cheers.

Antonio Alcalá

11-11-2006, 04:00 AM

Thanks Guillermo. Yes, I visited this url since 1 year ago comparing differents monohulls and stix numbers. Another day we could tell to forum my decision of buying a Beneteau Oceanis 473.

Best regards

SuperPiper

11-11-2006, 04:57 AM

About page 20 of the document is data for the etap 21i. It is a boat similar to my own micro-cruiser. The etap 21i is listed 4 times: 2x for its shallow keel and 2x for its deep keel. But the STIX rating for the deep keel version is 'C' with a heavier keel but using the Weight FL = 1816 kg as the ISO12217 Weight and again for the deep keel version is 'B' with the lighter keel but using the Weight MC = 1296 kg as the ISO12217 Weight.

I haven't studied the document. Guillermo, can you clarify this for me? Why would the STIX calculation use the Weight MC for one calc and Weight FL for the other?

Guillermo

11-11-2006, 03:34 PM

SuperPiper:
To say which one is the definitive STIX for a boat, calculations have to be done for the Minimum Operating Condition (MOC) and Full Load Condition (FLC), at least, and choose the lowest of the two values. And it may happen that a boat has less STIX when fully loaded than in the MOC condition.

But I think there is a mess with this Etap 21i four posts thing. On top of what you mention, there is also something curious: there are versions reaching B category with an STIX of 26, but one of them, with the same value only reaches category C (?)
And there is a gross mistake: that 120 STIX....

Because of this kind of misleading info, some contradictory data and the lacking of a lot of basic info for many boats, I think this RYA list has to be taken with great care.
Cheers.

Guillermo

11-11-2006, 04:58 PM

If you have a look at Contessa 32 and Etap 32S at RYA list, you'll find their STIX numbers as being 33 and 36. The 33 value for Contessa 32 is not trustable enough (maybe it is not even 32) and the Etap 32S STIX is in fact 35.7 not 36, so an additional reason not to trust the RYA list.

Contessa 32's stability curve presents a maximum GZ of 0,7 m at 78º and an AVS of 157º, with an irrisory negative area. D/L ratio is 310.

"Assent" a Contessa 32 skippered by Alan Ker came out pretty well of the '79 Fastnet race, being the smallest yacht to complete the race unscathed.

Etap 32S's curve presents a a maximum GZ of 0,6 m at 55º and the AVS is 122,5º with a significative negative area. Negative/positive areas ratio is around 0,2. D/L ratio is 185.

If we took from the Etap 32's STIX the effect of the 5 points given by its delta parameter (because of the floatation chambers I asume it has), figure comes down to a mere 30.7, so not reaching category A requirements.

Another cumulative proof of the weaknesses of STIX as a clue to seaworthiness.

Here an interesting comparison between the static stability of a Contessa 32 and a Half Tonner (Probably Nicholson designed "Grimalkin"), both participating at the '79 Fastnet Race: http://www.co32.org/BOAT_SECTION/STORIES/FASTNET_STUFF/fastnet.htm
You may find deeper comparisons between this two boats at Marchaj's book "Seaworthiness, the forgotten factor"

Cheers.

Vega

11-11-2006, 05:00 PM

So, in line with Crag Cay's concerns, here we have an example of forms that, although having proved their seaworthiness for decades, are penalized under the STIX (Compare with the Multichine 28 posted before)

P.S.: Interesting to note the great influence on STIX of surviving ability when flooded. If we could provide "Zara of Arran" with means to float when flooded, delta factor would be equal to 5 and so STIX would come up to 33,928 so neatly coming into Category A zone.

Guillermo, the Multichine 28 is not a Class A boat. The data provided was not verified and approved. The designer can say what he wants, but I seriously doubt that the boat has that STIX. You have verified the Data and the calculations?

STIX favors boats that are insubmergible, and that looks right to me. You can have a boat with a great stability but if you hit a container at full speed, unless you have a metal boat, or an insubmergible one, probably you will go down (of course, by the same criteria metal boats should benefit from the same criteria and I don’t think it is the case). But you give the impression that most modern boats use that criteria for the STIX ( I mean that they are insubmergible) and that is not the case.

Regards

Guillermo

11-11-2006, 05:44 PM

Guillermo, the Multichine 28 is not a Class A boat. The data provided was not verified and approved. The designer can say what he wants, but I seriously doubt that the boat has that STIX.
Why don't you ask him and let us know?

But you give the impression that most modern boats use that criteria for the STIX ( I mean that they are insubmergible)...
That's only your very active imagination...;)

On the flotability issue, I agree with you that floatation ability is an important safety one, but I would not use it to influence the STIX number in itself. I'd rather use an special notation for boats including this feature. Something like "Category A-F" or B-F or whatever. That would be more fair to compare the STIX numbers among different boats.

Cheers.

Vega

11-11-2006, 05:54 PM

Most people would think that by buying a more voluminous and apparently heavier cruising boat will have a safer boat than the sleek cruiser-racer from the same manufacturer.

That’s not the case, at least in what regards large production sail boats. I have said that referring the Bavaria Ocean line, comparing with the normal line of Bavarias, but here we have the same case with the Jeanneau 43 line. We can see that the cruiser-racer, the Sun-Fast has a better stability curve comparing with the cruising versions. The difference in displacement is minimal and don’t have any real influence on the stability of the different versions.

Cheers

Guillermo

11-11-2006, 06:05 PM

Another day we could tell to forum my decision of buying a Beneteau Oceanis 473.
Antonio, may I post my findings on the STIX and ratios for the 473, as to discuss them here?

Cheers.

Guillermo

11-11-2006, 06:14 PM

Vega

11-11-2006, 06:17 PM

Why don't you ask him and let us know?
.

I don't need.

If that boat was a Class A boat and approved as such we would say so.
What he says is not that the Multichine 28 IS a Class A boat but:

"The Multichine 28, differently from most boats of this size, CAN FIT at Category A ...

According to the stability index ( STIX) ...our design Multichine 28 belongs to category A...”

Next we show a résumé of the calculation and the STIX number for the MC28.

This means that according to those calculations, the boat has a STIX of 34.3 and therefore can fit category A....if those calculations are right;)

Guillermo

11-11-2006, 06:28 PM

I tend to rely on the word of reputed designers as Roberto Barros. But if you do not, well, it's up to you.
Anyhow I will ask him and bring his attention towards this thread.

Cheers.

Vega

11-11-2006, 06:51 PM

Paulo,
The better stability curve of the Sun Fast vs the Sun Odissey's one is because of the lower VCG induced by the deeper and bulbed keel. This increases STIX (Seeming to be 44 for the Odissey) although we should know what the effect of the increased sail area and higher CE (both bring down the STIX when their values increase) I stiil had no time to go through the Swans comparison, but that will be most interesting, as STIX seems to be clearly favouring long waterlined boats with deep, narrow bulbed keels.

Guillermo, as I have said, STIX number gives you just an idea, but if I have the boat stability curve and I know the boat, I don't use STIX to make an evaluation of a boat stability or his seaworthiness.

What I have said was: "the Sun-Fast has a better stability curve comparing with the cruising versions".

And you are right, that has to do with bigger draft and bulb weight.

About: "Stix seems to be favoring ....deep...bulbed keels"

I think that's the way it should be, because they lower the CG of the boat increasing RM and stability.

About:

"STIX seems to be clearly favoring long waterlined boats "

I will agree with you, even more if you add : “in detriment of displacement”.

What you are going to find with the Swans STIX is that the much bigger displacement (and RM curve) of the 46 is not sufficiently “favored” by the STIX formula, giving a completely false idea of the real stability of both boats.

Vega

11-11-2006, 07:16 PM

I tend to rely on the word of reputed designers as Roberto Barros. But if you do not, well, it's up to you.
Anyhow I will ask him and bring his attention towards this thread.

Cheers.

You do what you want but you know very well that a boat is only a CLASS A boat after being approved by a notified body or Classification Societies or whatever is the legal body that has the power to do so in the EC.

I was just pointing out that he didn’t say that his boat is a CLASS A boat, but that according with his calculations, the boat can be approved as a CLASS A boat.

As he says that one of those are being built in Europe (Portugal) we will soon know if the boat will be a CLASS A boat (or not).

regards

Guillermo

11-16-2006, 03:52 PM

Contessa 32 survided the Fastnet '79 . Here some estimated numbers for her:
(based on basic data available at: http://www.jeremyrogers.co.uk/index01.html and asuming Tc as 0.65 m and heeling arm as 6.0 m)

Length/Beam Ratio L/B = 2,7 being L=(0,7*Lwl +0,3* Lh) / Bmax
Ballast/Disp Ratio W/Disp = 0,48
Displacement/Length Ratio D/L = 307,04
Sail Area/Disp. Ratio SA/D = 20,06
Sail Area/Wetted surface SA/WS = 1,85
Power/ Disp. Ratio HP/D = 2,11 HP/ton
Hull speed HSPD = 6,56 Kn
Potential Maximum Speed PMS = 7,68 Kn
Velocity Ratio VR = 1,17
Capsize Safety Factor CSF = 1,85
Motion Comfort Ratio MCR = 26,46
Heft Ratio HF = 0,97

Angle of Vanishing Stability AVS = 137 º (Real: 157º)
Roll Period T = 2,67 Sec
Roll Acceleration Acc = 0,1 G's
Stability Index SI = 0,9
Dellenbaugh Angle DA = 28,77

Initial Metacentric height GMo = 0,71 m
Righting Arm 10º RA10 = 0,12 m
Righting Arm 20º RA20 = 0,22 m
Righting Arm 30º RA30 = 0,3 m

At Jeremy Roger's site STIX is not available and I've been informed by themselves they are unable to help about it (Curious, as they still produce this boat under order) :confused:

Vega

11-16-2006, 05:25 PM

Guillermo, the CONTESSA 32 STIX is 33 and the AVS 155.

Cheers

Guillermo

11-16-2006, 05:59 PM

Guillermo, the CONTESSA 32 STIX is 33
It is said to be 33. I'm not so sure now. See my post #132
Cheers.

Vega

11-16-2006, 06:45 PM

Guillermo

11-17-2006, 06:59 AM

But I asked Contessa manufactures in written and got their answer saying they are not able to help....

Vega

11-17-2006, 10:14 AM

Some manufacturers are very reluctant to make public the stability data of their boats. With some I can understand the reason, but with others I can not understand why. It happened to me with C-yachts, regarding the 12,5M. I like the boat and I have talked personally with them. They have said that they were sorry but their policy is not to disclose those data. Quite stupid, in my opinion, because I am sure that it is a boat with a good stability curve.

It is possible that the same thing applies to the guys from Contessa. The published STIX data (RYA) come from the IRC. If someone wants to race the Contessa those data have to be delivered to them, (or have a RORC STIX calculated). I think that is the way they have got it.

Guillermo

11-17-2006, 09:12 PM

Also posted at "Famous sinkings" thread, it deserves some comentaries here:

"The probe into the mystery of what sank the Moquini with a highly-experienced crew has uncovered a litany of procedural irregularities as well as alleged problems with construction in the keel area of the yacht."
More info at:
http://abyc.org.za/index.php/2006/09...hat_went_wrong
http://www.sundaytribune.co.za/index...icleId=3451851

The problem when adopting a narrow and deep keel for cruising is that something like this may well happen at any time. Even with a sound hull and proper keel-hull joint arrangement, if a container or the like is hit at relatively high speeds, keel may get lost, with all its consequences.

Should a boat like this be A categorized, even asuming good workmanship? (For an A category assessement, not only STIX is taken into consideration, but also structure -ISO 12215- as well as many other things).

Is it not seaworthiness... "The fitness or safety of a vessel for its intended use"? May we consider a long and narrow keel with a heavy bulb in its end, as being seaworthy from the point of view of this definition? (asuming the intended use is the RCD's one, not racing)

Vega

11-18-2006, 01:05 PM

The problem when adopting a narrow and deep keel for cruising is that something like this may well happen at any time.

Even with a sound hull and proper keel-hull joint arrangement, if a container or the like is hit at relatively high speeds, keel may get lost, with all its consequences.

¿Should a boat like this be A categorized..?

…May we consider a long and narrow keel with a heavy bulb in its end, as being seaworthy from the point of view of this definition?

Do you really think that fin bulbed boats should not be classified as class A boats? Or that a boat like that is not safe offshore?

Following that line of thinking, GRP or fiberglass boats, even if long keeled, should not be considered fit to go offshore and should not be classified as Class A boats. If they hit a container at full speed, they would not lose the keel, but the damage on the hull would be enough to sink them, anyway. Do you think that only metal long keeled boats are fit to go offshore?

I understand your personal preference regarding sailing boats but I think that it has an unrealistic influence in your global judgement about the seaworthiness of a sailboat. But this time it is far too much:p .

Besides, from what you say, we are led to think, that the Technical investigators have concluded that the design of the boat (Fin bulbed Keel) was responsible for the loss of the keel, or that the boat had hit a submerged object.

They say quite the opposite. The report says :

Several "possible contributing factors" were identified, including:

• sub-standard lamination of the hull near the keel;
• insufficient inspection of the hull condition;
• insufficient torque procedure to ensure the keel was secure;
• non-conformity to design specifications, and "poor workmanship".

The investigators asked the then Durban Institute of Technology to survey the hull and this revealed alleged discrepancies between the design of the yacht and how it was built.

The DIT reported that visual inspection and wall thickness testing showed, in the area of the keel, that the yacht did not conform to design specification and "the workmanship is appallingly substandard".

".. It is unlikely the yacht hit a container . . . because there would be damage to the hull elsewhere," the DIT study found.

" The investigators said a collision with a submerged object would have caused more damage to the hull than shown by the Moquini .”

It seems clear to me that the report points the blame not to the boat design, but to the non conformity of the boat to the Design specifications and to a workmanship that they consider: “appallingly substandard".

Guillermo, given the conclusions of the report I can not see how this example could serve the purpose of proving the inadequacy of fin keeled bulb designs for offshore sailing.

Guillermo

11-18-2006, 02:45 PM

Do you really think that fin bulbed boats should not be classified as class A boats? I'm just asking and you are again judging my intentions, as usual.

Or that a boat like that is not safe offshore?
But here I throw you here some fresh flesh: Definitely not for an all around globetrotter. :)

Cheers.

Guillermo

11-20-2006, 01:02 PM

Some data for this boat, with the 2.10 m keel, 3300 kg ballast version (Antonio Alcala's one):

Overall Hull Length = 14,16 m
Length Waterline = 13,35 m
Flooded Buoyancy (Y/N) = N
Beam Waterline = 3,9 m
Beam = 4,33 m
Displacement MSC = 12000 kg (estimative. Light:11500)
Height of CE above DWL = 6,47 m
Height of CLR below DWL = 0,64 m
Angle of vanishing stability = 126 deg
Downflooding angle = 110 deg (estimative)
GZ at downflooding angle = 0,323 m
GZ at 90 degrees = 0,569 m
Sail Area 114,38 = sq.m
Area to flooding (Agz) = 87,77 m.deg
Area to AVS = 91,5 m.deg

With these numbers STIX goes up to almost 60, very far away from the 48 figure provided with the info from the manufacturer. Lowering downflooding angle to 90º (not probable) and correcting GZ lever and area under GZ curve for this value, STIX comes down to around 50 (Another example of the utmost importance of this angle for the STIX calculation). We realize here the difficulty to check these calculations against the boayards' ones, as they don't provide enough data.

'Old' ratios and estimatives for her:

Length/Beam Ratio L/B = 3,14
Ballast/Disp Ratio W/Disp = 0,28
Displacement/Length Ratio D/L = 140,68
Sail Area/Disp. Ratio SA/D = 17,99
Power/ Disp. Ratio HP/D = 3,78 HP/ton (powerful engine)
Hull speed HSPD = 8,87 Kn
Potential Maximum Speed PMS = 9,73 Kn
Velocity Ratio VR = 1,18
Capsize Safety Factor CSF = 1,91
Motion Comfort Ratio MCR = 26,55 (pretty low)
Heft Ratio HF = 0,88
Angle of Vanishing Stability AVS = 115 º (Real: 126º, due to volumes over deck)
Roll Period T = 2,76 sec (better around 4,5 sec)
Roll Acceleration Acc = 0,16 G's (quite high)
Stability Index SI = 0,64 (quite low)
Dellenbaugh Angle DA = 13,56 º

Initial Metacentric height GMo = 1,40 m
Righting Arm 10º GZ10 = 0,24 m
Righting Arm 20º GZ20 = 0,44 m
Righting Arm 30º GZ30 = 0,60 m (coincides pretty well!)

So, although these last 'old' numbers are not a great deal for a boat intended to be a passagemaker, STIX goes high (relatively much higher than the other Oceanics), because of the low center of gravity (bulbed keel).

As we've seen before, STIX favours big positive areas under the GZ curve (due to low VCG in this case, as in all bulbed keelers), but does not take into account the negative-positive areas ratio (in this case over the maximum of 20% recommended by Andrew Blyth) and also, because of this and because it doesn't take into account inertias, categorises as blue water boats ones with very short rolling periods, as this one, which not only makes for uncomfortable movements, but also calls for dangerous situations when in breaking waves.

Antonio Alcalá

11-20-2006, 01:34 PM

Hello to all.After of conversations maintained between Guillermo and I, believe that serious a good idea commentaries on my decision. I will accept all and I will listen to you. After to review all the STIX, I bought Oceanis 473 because wanted a new boat, wanted to release it and I did not want a old model . But the reason for which me it buys it was, because he was the one that better quality price tapeworm, nonsingle of the market but also in relation to its STIX of all the Beneteau. By a STIX between 48-52 it is necessary to go away to nordics designs or yachts of very high cost.

Best winds

Antonio Alcalá

11-20-2006, 02:11 PM

Do you really think Oceanis 473 is the one of beneteau models that getting a real class A ( under 50 feet)?

Best winds

Guillermo

11-21-2006, 01:20 PM

Just a quick note to realize RCD is in fact influencing consumers minds (Took from IBI e-magazine):

"The RCD applies to any craft between 2.5m and 24m built or offered for sale in the EU and EEA (European Economic Area). It has been with us for a decade now, and has succeeded, according to the Department of Trade and Industry (UK), in creating a level playing field for marine manufacturers and traders across all 25 member states plus the EEA states of Norway, Iceland and Liechtenstein. It has also, says the DTI, raised the level of consumer confidence by addressing the essential aspects of a boat's design, construction and safety, evidenced by the CE Mark on the builder's plate."

The least that I can say is that consumers are trusting the RCD and, if a manufacturer categorizes a boat like A, that means, for the average consumer, it's an oceanic boat, so able to go anywhere. Risky business. :rolleyes:

P.S: May somebody (other than myself) give Antonio an opinion on the Oceanis Clipper 473? (His post has that intention)

fcfc

11-21-2006, 05:43 PM

The least that I can say is that consumers are trusting the RCD and, if a manufacturer categorizes a boat like A, that means, for the average consumer, it's an oceanic boat, so able to go anywhere. Risky business. :rolleyes:

No. You are on error on that. The potential buyer of a category A boat knows according to RCD that his boats will be able to survive over force 8 winds and over 4 m waves. But he also knows that RCD addresses neither range, nor comfort. In any RCD papers or category delimitation, all categories are listed by wind and vawe, not range or amenities.
And simply looking quickly at the market, given the difference between catgory A boat, from mini transat 6.5m to 30m swan, he will understand what category A means.
Now, if he is a complete dumb ass, you can put a law to forbid complete dumb ass to kill themselves, that wont prevent dumb ass suicide.

Guillermo

11-21-2006, 07:01 PM

The potential buyer of a category A boat knows according to RCD that his boats will be able to survive over force 8 winds and over 4 m waves.
No, my friend: He is induced to asume that! It is not truth at all that every single categorized A boat is able to resist over force 8 winds and over 4 m waves (7 m waves and force 10 winds as top limits).

Let's have a look at the Multichine 28 GZ curve (attached): This boat is said to have an STIX of 34.3 by its designer. So, if her structure fulfills also the requirements (not difficult to attain), most probably it will be Categorized as A (I wouldn't like to be the designer if his statements on this are not true).

But (in my humble opinion of course), the GZ curve presents an excessively big negative area, so the ability to recover after a B2 knock down is seriously threatened. With a Capsize Safety Factor of 2.1, a roll period of 2.03 sec (against a beam of 3.18 m), an Stability Index of 0.64 and a GMo around 1.39 m (so an steep angle of the curve at 180º) this boat may be posed in serious risk when encountering breaking waves of only 3-3.5 m on top of being probably uncomfortable and a crew punisher.

...And simply looking quickly at the market, given the difference between catgory A boat, from mini transat 6.5m to 30m swan, he will understand what category A means.
Are you sure the potential buyers of this boat are going to think like that? In my opinion they just will trust the RCD and the designer, that's it. And they will go happily globetrotting!

Cheers.

Antonio Alcalá

11-22-2006, 06:37 AM

Most of buyers in my opinion are looking for yatchts with high level of security, and of course marcation CE "A". I mean most of the ocean yachtmaster of Spain. I mean too, most of ocean yachtmaster prefer a new boat and released it that find problems in old designs, wich could be safer according to classic rules, but with problems in another places of the boat. That means money and time.Moreover, most of my fellows prefer a speed cruiser with higher roll periods but with the ability of escape of low pressure systems. Speed is safe too if the helmman is equally fast. But the question is: What is in your opinion a true security number of STIX for blue water cruiser? And secondly: Is the marcation CE the right form of measuring the capacities of a yacht in heavy weather? Why boats wich are A, don´t have in any case these capacities mainly in bad weather with medium waves?
And finally are we in a great mascarade?:confused: if outside thus, we should claim before official organisms : people begin being satiated with deceits

Waiting for your response

Vega

11-22-2006, 11:04 AM

Olá António,

Your post is not big but to answer to all your questions it would be necessary a huge one:rolleyes: .

old designs, which could be safer according to classic rules, but with problems in another places of the boat.

That’s a myth. Some of the old boats are still good boats but most of them are just old and outdated designs. Most of them are slow, heavy, undercanvased boats, with old rigs (that in many cases need a complete substitution) and they have reefing systems that need the presence of a crew man at the foot of the mast, a situation that can be dangerous in troubled seas. It is true that they are normally more comfortable (because they are heavier) in a seaway.

Most of my fellows prefer a speed cruiser with higher roll periods but with the ability of escape of low pressure systems.

The difference in speed between one of those old and heavy boats and a fast cruiser can be very considerable and in that case there is some truth in that. But comparing with your boat that difference will be no more than 2 knots, and I don’t think that it will be important, regarding the ability to escape low pressure systems.

Regarding the roll periods of those boats, they would be a little higher than in your boat, but not much, and that has to do with comfort and not with seaworthiness (unless you get seasick at sea). If the difference in roll period can be considerable between your boat and an old and heavy one (making the older one more comfortable), I don’t believe that you would feel a significant difference in comfort, comparing your boat with a sport cruiser, like the First 47.7, in what concerns rolling.
In this kind of (modern boats) the amount of difference in forefoot is more important regarding comfort.

As I have shown in this thread (see the comparison between the Jeanneau 44), regarding seaworthiness, normally for big production boats, and for the same range, the sports boat is not less seaworthy than the cruiser boat and sometimes it is even more. On the other hand, the superior sailing area will make it a boat more difficult to handle and a boat that will need a lot of reefing work (not that it will be more difficult to reef, just that you will need to do that a lot more times).

What is in your opinion a true security number of STIX for blue water cruiser? And secondly: Is the marcation CE the right form of measuring the capacities of a yacht in heavy weather? Why boats wich are A, don´t have in any case these capacities mainly in bad weather with medium waves?

I would say 40, with a minimum weight of 5T and a minimum AVS of 120º.

Stix number, with a minimum AVS and a minimum weight is the best general rule they could provide to make an evaluation of sailing boats stability and seaworthiness.
Personally I find that displacement has not the importance it deserves in the STIX calculation.

The Dehler 29 is a very good boat, but with a weight of around 3T do you really think that the boat will be safe sailing in force 10 winds and 7m waves? I would like to put all the guys responsible for the actual criteria that define Class A boats, inside a Dehler 29 in those weather conditions:D .

Probably not, because you are a sailor, but if you where a kid buying his first cruiser boat, coming from dinghy sailing and knowing very little about the ocean or boats, why should he not believe in that official certification? And armed with that false assurance expose himself (and others) to dangerous situations that could end in tragedy?

And finally are we in a great mascarade?:confused: if outside thus, we should claim before official organisms : people begin being satiated with deceits.

Yes, certification of anything regarding safety should be a serious matter (and in my opinion this one is not credible).

But one thing is the certification which advises you about what is officially considered safe, another thing is the freedom of setting sail in a boat of your choice.

I am for the responsible advice, but also a defender of the individual liberty. The advice should be one that you follow or not, and should have nothing to do with the freedom and possibility of sailing in the boat of your choice to where you want;) .

Saludos

Crag Cay

11-22-2006, 11:57 AM

Hi Vega, Guillermo et al. I really do mean to write something about the nature of the information that should be provided to the buying public with all new boats. I will post it in Guillermo's new thread about this.

However, a couple of points you made here does illustrate the limitations of the current system. Vega here has prioritised displacement in a 'seaworthy vessel' where others might put more emphasis on something else. But by lumping all these criteria into one correct 'answer' (either Category or even STIX, etc), we must all either concur what these qualities should be, or be happy to allow other 'learned people' to prescribe an answer for us.

My alternative, which I will expand on in the other thread, is to keep the information about all the qualities of the boat separate. Give the buyer details on the boat's strength, resistance to knockdown, comfort factor, weatherliness, recovery from 90 degrees, behaviour if rolled, susceptibility to crash damage, etc, etc. Then the buyer can choose where to make his own trade offs.

This system works with cars: Basic legal standards prevent total junk being placed on the market (an equivalent role to the RCD) but then the buyer is left to judge, with the help of reviews and third party standards (such as NCAP safety), which of the models offered by the manufacturers is the most suitable for their needs. Some will decide a 'safe car' has lots of air bags, while others might prefer more active safety with better handling and brakes.

If we are happy that the public can make these sorts of judgments with something as dangerous as driving, we can certainly allow them to make a similar judgment with boats. After all, sailors are still haunted by the 19 deaths in the Fastnet disaster 27 years ago, but society as a whole is not unduly troubled by the same number who have died on UK roads since yesterday.

Antonio Alcalá

11-22-2006, 01:36 PM

Vega, we have something in common. The necessity to prioritize in the security of a yacht beginning by its same design. Active, passive security, but also design. The design is very important. Design save lives.I am convinced of it because I sail 28 years ago, and the last 8 sailing alone.
I enterely agree with you except in the STIX number and weight. For me would be 50 the right number for maximum security and 8.5 T at least.
You fall to me well, but don´t know if it is right my expression :?: in english.
Tell me more things

Best winds

A.

fcfc

11-22-2006, 03:27 PM

The Dehler 29 is a very good boat, but with a weight of around 3T do you really think that the boat will be safe sailing in force 10 winds and 7m waves? I would like to put all the guys responsible for the actual criteria that define Class A boats, inside a Dehler 29 in those weather conditions:D .

It depends.
I have sailed for some years. In race. I can tell you from experience that force 8, 4-5 m v=waves, in a IOR half tonner, can be very very different depending on condition.
One was a saturday afternoon race, with the usual crew of the boat. In tropical waters. Force 8 tradewinds. Heavy ocean waves. Water temp 26°c, outside temp over 30°C. All crew on deck. The memory I have tacking with 2 reefs, jib n°2 was wet, but fun. Surfing under spi was even more fun. (we did not blast the spi, and we did not put the spreaders in the water ...)

The second remind I have was also a race. A "long range" race, about 200 nm. It was in April, in britanny. The crew was an assembly crew gathered for that race. I pulled the shortest straw to be on deck at 2 AM, in the night. The deck was slippery/icy on the early morning. One member of the crew was seasick by lack of training after winter. The wind was force 8, wave 4-5m. The boat was also an IOR half tonner.
I do not have at all the same memory from this race.

Vega

11-22-2006, 03:55 PM

My alternative, which I will expand on in the other thread, is to keep the information about all the qualities of the boat separate. Give the buyer details on the boat's strength, resistance to knockdown, comfort factor, weatherliness, recovery from 90 degrees, behaviour if rolled, susceptibility to crash damage, etc, etc. Then the buyer can choose where to make his own trade offs.

This system works with cars: Basic legal standards prevent total junk being placed on the market (an equivalent role to the RCD) but then the buyer is left to judge, with the help of reviews and third party standards (such as NCAP safety), which of the models offered by the manufacturers is the most suitable for their needs. Some will decide a 'safe car' has lots of air bags, while others might prefer more active safety with better handling and brakes.

If we are happy that the public can make these sorts of judgments with something as dangerous as driving, we can certainly allow them to make a similar judgment with boats. After all, sailors are still haunted by the 19 deaths in the Fastnet disaster 27 years ago, but society as a whole is not unduly troubled by the same number who have died on UK roads since yesterday.

I agree, but unless you are a very powerful man in the “system” and have a lot of back up, the possibilities of implementing that, should be near 0.

That was possible with cars AGAINST the initial will of almost all manufacturers because people started to get conscious about it and mainly because Volvo had made a banner of the safety of their cars and were rewarded in sales. All this together and decades were needed to arrive to the comparative safety tests between several models from the same segment.

It is obvious that what you want is against the interest of the companies that sell 90% of the market sailboats.

Of course, the situation would change if a middle-sized company started a commercial sales strategy based in safety, like the one Volvo has done in the 70’s and 80’s, and if that strategy paid in sales. Anyway you would have to wait many years.

And they would have to produce safe boats for a price that would not be more than the double of the prices of their market competitors (as it is now) and, as you know, that would be difficult.

Giving the odds, I think it is much easier and effective to stick to the actual system (STIX, minimum displacement and minimum AVS), but demanding more credible and responsible criteria. I think this would be a lot easier to manage and without being perfect, would provide a base for future and more demanding improvements.

...couple of points you made here does illustrate the limitations of the current system. Vega here has prioritised displacement in a 'seaworthy vessel' where others might put more emphasis on something else.
.

You have misunderstood me. I have not, “prioritised displacement in a 'seaworthy vessel”

You should know by now that I don’t prefer heavy boats.

What I have said was:

Personally I find that displacement has not the importance it deserves in the STIX calculation..

This does not mean that I prioritise displacement, and in fact I do not, but as you, I prioritise Righting Moment (“resistance to knockdown, recovery from 90 degrees”) and the righting moment is obtained multiplying GZ x Displacement.

I have said that the displacement has not the importance it deserves in the STIX calculation. That’s because, for the calculation of the Dynamic Stability Factor (part of the STIX formula that represents the global boat stability), it is not the area behind the RM curve (the one that measures the amount of force needed to capsize the boat) that is considered (that one is obtained multiplying the values from the GZ curve by the displacement of the boat) but the area under the GZ curve. That value, instead of being multiplied by the displacement, is multiplied by the length of the boat. The length of the boat has little to do with the boat’s stability.

I prefer light boats, but I try to be impartial and it is obvious that heavier boats have STIX numbers that don’t represent their true stability. This is the case with, for instance, the Island Packets or with the Swan 46, a boat that obviously has bigger RM values than his racing brother, the lighter 45 and this one, nonetheless has a bigger STIX number.

Take a look at Post 121, where the GZ curves of both Swans were posted and calculate the RM values for both boats. You are going to see what I mean.

See also the post 122 where Guillermo presents some justifications for this situation (quoting Eliasson).

But facts are facts and I am not the only one saying that STIX number relies too heavily on the boat’s length, other more knowledgeable persons have said the same.

Crag Cay

11-22-2006, 05:05 PM

Vega - I'm sorry if I misrepresented you, and I agree with most of what you say. However, all the problems you describe are a function of trying to reduce too much information down to one number. It always amuses me that boat designers have this fascination with these complex formulae and their inherent trade offs. I suppose as we work with rating rules, handicaps, scantlings schedules and the like, on a daily basis we think this sort of thing is 'normal'. But I think it alienates ordinary boat people who don't share our love of finding the most 'efficient' way of reaching some arbitrary target value.

For all this information to be accessible to the buying public, it should be presented to them in answer to all the natural questions they have when looking for boat. The figures are available anyway, so wouldn't require more disclosure by the manufactures, but at the moment the relevancy of this information is lost when stirred together into the 'pot purri' of STIX or Categorisation.

So, as I mentioned before, we need to answer, in an accessible way, these types of questions: How strong is this boat, how stiff, how weatherly, how comfortable, how fast, how self righting, how susceptible to damage, etc?

The other problem with having one defined standard such as 'It's Cat A', is that in the short term it may lift standards but then, why would a manufacturer go to the expense of exceeding the base line value? After all, Cat A is Cat A. My 'sub sets' of information would all be open ended scales which would recognise excellence. It would let some manufactures demonstrate the particular qualities of their boat, and if the market responded, it would put pressure on the others (your Volvo syndrome). But lesser boats would not fail, as the consumer could still choose the level of prevision that suited them. In the same way plenty of people still buy cars without ABS and only one air bag. Simply raising the bar for everyone just increases costs across the board and stigmatises 'failures', which otherwise might suit some people's needs perfectly well.

My dissatisfaction with these 'trade off' formulae originated with the RORC Safety and Stability Screening Numbers. My race boat had a Base Value below the minimum required for some offshore races in Scotland. I was however allowed the maximum Adjustment Value to bring her up to compliance as I was able to impress the Measurer with various modifications we had made. However, none of these modifications actually addressed the short comings of the boat. They were 'fudges' that beat the system - but done at the behest of the safety authority. Needless to say, the safety regime I instigated as a responsible skipper, hardly relied to any meaningful degree on the 'required features'.

So I think the RCD should be left alone. As the Dept of Trade said, it's done its job in easing the hassles of selling a boat throughout all the EEA countries . It's also claimed to have began to help the consumer. So let's build on this second point by developing an information system that is accessible, meaningful, workable and allows the consumer to really make sound choices in the boats they want to buy. The consumer's needs should be the driving force for this process and not just to allow another oppurtunity for boat designers to fiddle with formulae.

Guillermo

11-22-2006, 05:57 PM

all the problems ... are a function of trying to reduce too much information down to one number...

...the relevancy of this information is lost when stirred together into the 'pot purri' of STIX or Categorisation.

So, as I mentioned before, we need to answer, in an accessible way, these types of questions: How strong is this boat, how stiff, how weatherly, how comfortable, how fast, how self righting, how susceptible to damage, etc?

... developing an information system that is accessible, meaningful, workable and allows the consumer to really make sound choices in the boats they want to buy. ...

YES! :)

(Anxiously waiting for your posting at the other thread)

Vega

11-22-2006, 06:18 PM

It depends.
I have sailed for some years. In race. I can tell you from experience that force 8, 4-5 m v=waves, in a IOR half tonner, can be very very different

Fcfc, I was talking about force 10 wind and 7m waves. These conditions have nothing to do with the ones with force 8 and 4/5m waves.

With force 8 and 4m waves the Dehler would not have any problem.

A friend of mine sails regularly with a Beneteau 27 on conditions like that...solo. I have sailed some times with those conditions on my old traditional wooden 25ft sailboat.

Those conditions are the upper limit for Class B boats.

The conditions that a class A boat should be capable of handle are very different.

From the RECREATIONAL CRAFT DIRECTIVE:

ANNEX I: Essential Requirements

ESSENTIAL SAFETY REQUIREMENTS FOR THE DESIGN AND
CONSTRUCTION OF RECREATIONAL CRAFT

1. BOAT DESIGN CATEGORIES

Article 3 of the Directive : Essential Requirements

The products referred to in Article 1 (1) shall meet the essential safety, health, environmental protection and consumer protection requirements set out in Annex I.

Design Categories

A. OCEAN: Designed for extended voyages where conditions may exceed
wind force 8 (Beaufort scale) and significant wave heights of 4 m and
above, and vessels largely self-sufficient.

B. OFFSHORE: Designed for offshore voyages where conditions up to, and
including, wind force 8 and significant wave heights up to, and including, 4m may be experienced.

The Design Category parameters are intended to define the physical conditions that might arise in any category for design evaluation….For Category A, extreme conditions apply as they reflect that a vessel engaged on a long voyage might incur any conditions ]and should be designed accordingly, excluding abnormal weather conditions e.g. hurricane."

Note: the bold marks are mine.

Vega

11-22-2006, 06:57 PM

It always amuses me that boat designers have this fascination with these complex formulae and their inherent trade offs.

For all this information to be accessible to the buying public, it should be presented to them in answer to all the natural questions they have when looking for boat. The figures are available anyway, so wouldn't require more disclosure by the manufactures, but at the moment the relevancy of this information is lost when stirred together into the 'pot purri' of STIX or Categorisation.

It's also claimed to have began to help the consumer. So let's build on this second point by developing an information system that is accessible, meaningful, workable and allows the consumer to really make sound choices in the boats they want to buy. The consumer's needs should be the driving force for this process and not just to allow another oppurtunity for boat designers to fiddle with formulae.

Yes I agree with most of what you say. But far meaningless than STIX (regarding stability assessment) were what Guillermo calls “Old Ratios”. Those were very inaccurate tools that are only applicable (and very roughly) to a certain type of boat. They are meaningless if applied to modern bulbed sailboats.

The information that you say is available, is not. The sellers will not have a clue about what you are talking about and the boat manufacturers don’t disclose that information to the public. You have to ask for it, and sometimes they give it to you, others they don’t.

I believe you are overestimating the average knowledge of the typical boat buyer. Fact is that even professional specialized press, completely disregard the information about safety stability in the boats they are testing for their magazines. Even the British press that usually publish the GZ or RM curves of the boats they test, don’t make any comments about them, neither when they are very bad, nor extremely good.

If these guys don’t really know how to interpret those data, how do you expect the average buyer to do it?

STIX has the advantage of simplicity in its interpretation, the bigger the better, and even if far from perfection, it can give you an approximate idea of the boat’s stability. Better than nothing, I would say.

Vega

11-22-2006, 07:06 PM

.I am convinced of it because I sail 28 years ago, and the last 8 sailing alone.
I enterely agree with you except in the STIX number and weight. For me would be 50 the right number for maximum security and 8.5 T at least.
.

Thanks António,
Regarding STIX and Class A bots, I was not talking about Maximum Security, but about Minimum requirements for a Class A boat.

About the Oceanis 473, your intention is sailing it solo?

Cheers

Guillermo

11-23-2006, 01:11 AM

But far meaningless than STIX (regarding stability assessment) were what Guillermo calls “Old Ratios”. Those were very inaccurate tools that are only applicable (and very roughly) to a certain type of boat. They are meaningless if applied to modern bulbed sailboats.

I'm afraid I do not agree. 'Old ratios' were and still are a good tool to judge how a boat will behave at sea for certain aspects. And they also apply to modern bulbed sailboats, of course. Read again post 151 about Antonio's boat numbers. Oceanis 473 is a bulbeb keeler and her 'Old ratios' give a pretty good idea about the boat. Even the estimated GM and the GZs at 10º, 20º and 30º (based in simple estimatives) coincide quite well with the real curve's values.
Only AVS has to be taken with care because it usually gives values under the real thing, as it doesn't take into account volumes over deck. Even though it's a nice tool to judge a boat against other.
'Old ratios' are incomplete from the point of view of ultimate stability (they are more oriented towards initial stability) except for the CSF. And even this one has proven to be quite a good guide. I've studied both the Final Report of the Directors and the Inquiry about the '79 Fastnet Race and I find the approach to the CSF formula at the report (named 'capsize screen value' there) to be very valid.
I find STIX a much more misleading info than 'Old' ratios, as we have seen thoroughly through this thread.
If you have examples to support your statement with numbers, I'd appreciate your posting here.
Cheers

fcfc

11-23-2006, 04:44 AM

Fcfc, I was talking about force 10 wind and 7m waves. These conditions have nothing to do with the ones with force 8 and 4/5m waves.

With force 8 and 4m waves the Dehler would not have any problem.

I agree. I was simply pointing that the perception of bad/good weather could be changed by other characteristics than the boat, wind force and waves heigh.

Antonio Alcalá

11-23-2006, 07:03 AM

Yes,Vega, I sail on 473 since 2005 March.Most of the times alone. I´ve been in a gale with 52 kts and 4 meter waves close to Isla de Alboran. I had no problems with the boat, very strong, very safe and even more very fast.I did escape of a low pressure system at 11.5 knots only with main sail 2 reefs and storm sail. All were perfect while steering at 120-130 º of wind. First example where I could prove to myself, the safety of speed for escaping a gale. Do you think that it had the same with a heavy weight boat?

Best winds

rayk

11-24-2006, 01:23 PM

overestimating the average knowledge of the typical boat buyer. Fact is that even professional specialized press, completely disregard the information about safety stability in the boats they are testing for their magazines. Even the British press that usually publish the GZ or RM curves of the boats they test, don’t make any comments about them, neither when they are very bad, nor extremely good.

If these guys don’t really know how to interpret those data, how do you expect the average buyer to do it?Its a graph dude. The data (numbers) has been interpereted into a graph. If the buyer is reading new boat reviews, they have money, and reading graphs goes with the territory.

STIX has the advantage of simplicity in its interpretation, the bigger the better, and even if far from perfection, it can give you an approximate idea of the boat’s stability. Better than nothing, I would say.A single number doesnt tell me more than a RM graph.

Average boat buyer is learning all the time and devotes a lot of time to studying. Boat owners understand more than you give them credit for. Buyers are more likely to understand a boats character and make a reasonable judgement, without this new layer of calculations.
STIX is a sum of so many variables it is meaningless. Two different boats with the same number,and one of them is going to look obviously more suitable for the conditions in mind to the prospective customer.
If all the input data for STIX was available to prospective buyers, they could make informed choices trading off good and bad points between boats. These basic numbers arent always available and old ratios are therefore difficult to compute when consumers really want to compare boats. If it is so difficult to obtain basic data for a boat in the market now, a new emperical number defining stability is not needed.

A broker selling foolproof boats with safety numbers/factors/ratios is the surest way of leading lambs to the slaughter.

By the way whats the STIX for Slocums Spray, it must be crap. Or Wanderer III how does that rate?:p

Guillermo

11-24-2006, 06:16 PM

A single number doesnt tell me more than a RM graph.
Knowing the GZ curve, displacement and downflooding angle, one can get a lot of precise info on the stability based aspects of a boat's seaworthiness. I dare to say that more useful info than just knowing the STIX, if one knows what to look at.
Cheers

Guillermo

11-25-2006, 02:43 PM

The Efes 56, designed by Dijkstra, is the type of cruising sailboat I would love to own (http://www.efesyat.com.tr/project.html)
(probably not water ballasted, but maybe lifting-keeled as precursor Bestevaer 56 is)

Here some estimated numbers for her:
(main characteristics as per YW magazine, not the designer's nor the builder's sites. All three differ from each other :confused: )

Length/Beam Ratio L/B = 3,44
Ballast/Disp Ratio W/Disp = 0,3 (with water ballast. without it is 0,25)
Displacement/Length Ratio D/L = 177,51
Sail Area/Disp. Ratio SA/D = 18,73
Sail Area/Wetted surface SA/WS = 2,31
SA (metric)/ Power (Imp.) SA/HP = 1,96
Power/ Disp. Ratio HP/D = 1,52 HP/ton (auxiliary engine)
Hull speed HSPD = 9,46 Kn
Potential Maximum Speed PMS = 10,34 Kn
Velocity Ratio VR = 1,09
Capsize Safety Factor CSF = 1,65
Motion Comfort Ratio MCR = 39,17
Heft Ratio HF = 1,19

Angle of Vanishing Stability AVS = 117 º
Roll Period T = 4,06 Sec
Roll Acceleration Acc = 0,08 G's
Stability Index SI = 0,88
Dellenbaugh Angle DA = 20,36

Initial Metacentric height GMo = 0,73 m
Righting Arm 10º RA10 = 0,13 m
Righting Arm 20º RA20 = 0,23 m
Righting Arm 30º RA30 = 0,31 m

CG height, KG = 1,13 m
Position CG to WL, KG – D = 0,24 m (over floatation)

Heeling Moment at 20º HM20 = 36948,94 Ft*pound
Wind pressure coefficient WPC = 1,01

Does anybody have her stability curve, to try to calculate her STIX? (not available anywhere)

By the way, at YW magazine's last issue there is a nice comparative analysis of Dehler 44, Grand Soleil 43 and Maxi 1300, and STIX is not even mentioned for any of them. Interesting.

Interesting also what YW says about the target market for this new breed of light and fast cruisers: "...(their builders) identify their typical customers as sailors for whom the chunky go-anywhere yacht is overkill for an annual diet of weekend sailing and two week family holidays..."

Down here a picture from Efes 56. Beautiful!

Antonio Alcalá

11-28-2006, 11:20 AM

Could anybody bring us, the stability curves and STIX of the Vellux 5 Oceans 60 feet?. We could compare designs. Hugo Boss capsized!

Best winds

Guillermo

11-28-2006, 04:15 PM

Let's analize here one of those modern fast french cruisers, 'A' categorized, from a top designer:
The interesting tween-keeler RM 1200, designed by Marc Lombard (http://www.marclombard.com/)

Input data:

Overall Hull Length = 11,99 m
Length Waterline = 11,42 m
Flooded Buoyancy (Y/N) = N
Beam Waterline = 3,8 m (asumed)
Beam = 4,22 m
Displacement MOC = 6876 kg
Displacement Max = 7800 kg
Height of CE above DWL = 6,51 m
Height of CLR below DWL = 0,51 m
Angle of vanishing stability = 116 deg
Downflooding angle = 100 deg
GZ at downflooding angle = 0,21 m
GZ at 90 degrees = 0,33 m
Sail Area = 86,67 sq.m
Area to flooding (Agz) = 53,7 m.deg
Area to AVS = 55,71 m.deg

Here some estimated numbers and Ratios for her:

Length/Beam Ratio L/B = 2,75
Ballast/Disp Ratio W/Disp = 0,33
Displacement/Length Ratio D/L = 146,08
Sail Area/Disp. Ratio SA/D = 22,39
Hull speed HSPD = 8,20 Kn
Velocity Ratio VR = 1,19
Capsize Safety Factor CSF = 2,15
Motion Comfort Ratio MCR = 20,94
Heft Ratio HF = 0,71
Angle of Vanishing Stability AVS = 115 º
Roll Period T = 2,13 Sec
Roll Acceleration Acc = 0,26 G's
Stability Index SI = 0,5
Dellenbaugh Angle DA = 9,07

And now, asuming the downflooding angle is the minimum required for Category A, i.e. 100º (as this data is not available), we can estimate her STIX at this angle, what we may call the STIX(100)

Base Length Factor (LBS) = 11,610
Displacement Length Factor (FDL) = 0,937
Beam Displacement Factor (FBD) = 0,957
Knockdown Recovery Factor (FKR) = 1,053
Inversion Recovery Factor (FIR) = 0,961
Dynamic Stability Factor (FDS) = 0,981
Vaw = Not aplicable
Wind Moment Factor (FWM) = 1,000
Downflooding Factor (FDF) = 1,111
Delta = 0

STIX (100) = 32,920
Very low figure for the size. Realize how most of STIX's factors are under 1,000. Increasing Dfl to 116º (=AVS) only brings STIX up to 33,531

An interesting boat, no doubt, with some interesting features. But from my point of view, with that huge beam it will result cruel to her crews when at displacement speeds or at anchor, and not safe at all when at open ocean, with that high negative area at the GZ curve (32% of the positive!), maximum negative GZ slightly bigger than the 50% of her maximum positive GZ, maximum GZ at around 50º and low GZ at 90º.
I wouldn't like at all to experience a B2 knockdown with this boat!

Cheers

Guillermo

11-28-2006, 06:11 PM

And here some first numbers for POGO 40 Cruiser (I have no data to estimate her STIX, but I guess is probably as low as the RM's one):

Length/Beam Ratio L/B = 2,74
Ballast/Disp Ratio W/Disp = 0,34
Displacement/Length Ratio D/L = 84,91
Sail Area/Disp. Ratio SA/D = 30,09
Hull speed HSPD = 8,42 Kn
Velocity Ratio VR = 1,33
Capsize Safety Factor CSF = 2,55
Motion Comfort Ratio MCR = 12,92
Heft Ratio HF = 0,44
Angle of Vanishing Stability AVS = 115 º
Roll Period T = 1,66 Sec
Roll Acceleration Acc = 0,44 G's
Stability Index SI = 0,38
Dellenbaugh Angle DA = 16,57

Things are even worse. Really dangerous when not in planning conditions (*). I'm really curious to know the GZ curve of this boat.

Cheers

(*) Or even in planning if you lose control, whatever the reason. And when running fast and furious at 20 kn, I wouldn't like to hit a whale, container, log or whatever!)

Guillermo

12-04-2006, 06:34 PM

Some statistics for the Capsize Safety Factor and the Motion Comfort Ratio:
(Taken from Johnsboatstuff. Analysis based on 777 boats)

Capsize risk, usually below two for cruising boats, is strongly related to LOA. The longer boats are heavier and have less beam, which greatly reduces capsize risk. Its fairly uncommon for a boat longer than 40 feet to have a capsize value greater than two. For MCR again longer boats clearly have an advantage.

See attached charts of CSF and MCR plotted vs LOA (ft)

Mikey

12-04-2006, 10:14 PM

And here some first numbers for POGO 40 Cruiser (I have no data to estimate her STIX, but I guess is probably as low as the RM's one):

Length/Beam Ratio L/B = 2,74
Ballast/Disp Ratio W/Disp = 0,34
Displacement/Length Ratio D/L = 84,91
Sail Area/Disp. Ratio SA/D = 30,09
Hull speed HSPD = 8,42 Kn
Velocity Ratio VR = 1,33
Capsize Safety Factor CSF = 2,55
Motion Comfort Ratio MCR = 12,92
Heft Ratio HF = 0,44
Angle of Vanishing Stability AVS = 115 º
Roll Period T = 1,66 Sec
Roll Acceleration Acc = 0,44 G's
Stability Index SI = 0,38
Dellenbaugh Angle DA = 16,57

Wow! Seems like the Sea Worthiness thread is more needed than what most people think :)

Guillermo, Thanks for your effort in this area

Mikey

Antonio Alcalá

12-05-2006, 08:22 AM

Here you have a complete list of Beneteau, except some models, with their STIX. As you can see, the best relation between price and security is the 473. Very impressive how some models do not surpass the right STIX in comparation with LOA. Very impressive too how much of them have Category CE A, and however score with a minimum limit of ISO STIX 12217.

Let´s cross oceans with them and let´s pray for us!

ISO STIX 12217

Beneteau 57 53
Beneteau 50 41
Beneteau 473 51
Beneteau 461 37
Beneteau 44CC 34
Beneteau 423 38
Beneteau 411 37
Beneteau 393 43
Beneteau 381 38
Beneteau 373 36
Beneteau 36CC 35
Beneteau 361 32
Beneteau 351 35
Beneteau 343 34
Beneteau 331 28
331 New version 32
Beneteau 323 26
Beneteau 321 33
Beneteau 311 27
Cyclades 39 38
Cyclades 43 36

Figaro 2 33
Beneteau First
Beneteau First 25,7 22
Beneteau First 26 22
Beneteau First 27,7 28
Beneteau First 31,7 30
Beneteau First 33,7 32
Beneteau First 36,7 34
Beneteau First 40,7 37
Beneteau First 42,7 35
Beneteau First 44,7 41
Beneteau First 47,7 46

Any comments guys?

Best winds

Antonio

Guillermo

12-05-2006, 10:25 AM

Thanks for your kind words, Mikey :)

Antonio: Nice Job!
Only the 473 and the 393 have a reasonable STIX for their length. Beneteaus are rather conceived as light, comfortable (home-like) and relatively cheap coastal cruisers than all weather bluewater globetrotters. I'll try to join info from other manufactures going the other way round (as Pacific Seacraft, i.e) and post it here.

As finding Pacific Seacraft info for their STIX is not going to be easy (somebody may help?), in the mean time here some info for Island Packet Yachts models http://www.ipy.com/

Model ------ LOA (ft) --STIX
SP Cruiser --- 41' 1" ----- 39
IP 370 ------- 37' 10" --- 43
IP 440 ------- 45' 9" ---- 52
IP 445 ------- 45' 9" ---- 53
IP 485 ------- 51' 7" ---- 66

Cheers

Guillermo

12-05-2006, 10:59 AM

Very interesting analysis on canting keels and stability (With their impact on STIX):
http://www.yachting.org.au/site/yachting/ayf/downloads/Technical/Agendas/Stability-Appendices%20to%20the%20submission/Appendix%206%20Reichel%20Pu~0008.pdf

Interesting to note how the STIX diminishes when canting the keel either the side, in spite of some increases in overall stability, as it is not conceived for this kind of keels.

A nice example of how we neither shouldn't do simplistic interpretations of the STIX number, nor of GZ curves:

From there:
"The negative values from the GZ curve are only an indication of the direction of rotation and not of inverted stability. The fact that, in a yacht with the keel on centerline position, the range of inverted stability coincides with the negative GZ values has led to the misconception that it is true for all GZ curves."

I also attach the document, just in case the address has any problems.

Cheers

Guillermo

12-05-2006, 11:07 AM

Another interesting sailboat under 30' with STIX over 32, having a totally positive GZ curve:
The Scanyachts 290, derived from the LM27
http://www.scanyachts.co.uk/290b.htm

Cheers

Crag Cay

12-05-2006, 11:51 AM

Hi Guillermo - I guess that's with the pilothouse door shut and all the windows remaining intact? Do you think both these factors are a certainty if its rough enough to roll 360?

With regard to the canting keel article, the 'villains of the piece' again seem to be excessive beam and inadequate engineering of the keel. Do you know of any canting keel boats that have remained inverted with their keels fully intact and the control systems still operating?

Antonio Alcalá

12-05-2006, 12:12 PM

Excellent documents Guillermo, both are really interesting. Everyday I learn something in this forum.

West winds ( if your are on parallel 40º)

Antonio Alcalá

12-06-2006, 04:27 AM

Could we imagine an ARC to Europe with any designs of Beneteau in bad weather?

Do we do the right without claiming more security to the ARC Head Office ?

Do we need a "little Sidney-Hobart" during the ARC for having clear ideas about what is right and what no?

ISO STIX 12217

Beneteau 57 53
Beneteau 50 41
Beneteau 473 51
Beneteau 461 37
Beneteau 44CC 34
Beneteau 423 38
Beneteau 411 37
Beneteau 393 43
Beneteau 381 38
Beneteau 373 36
Beneteau 36CC 35
Beneteau 361 32
Beneteau 351 35
Beneteau 343 34
Beneteau 331 28
331 New version 32
Beneteau 323 26
Beneteau 321 33
Beneteau 311 27
Cyclades 39 38
Cyclades 43 36

Figaro 2 33

Beneteau First

Beneteau First 25,7 22
Beneteau First 26 22
Beneteau First 27,7 28
Beneteau First 31,7 30
Beneteau First 33,7 32
Beneteau First 36,7 34
Beneteau First 40,7 37
Beneteau First 42,7 35
Beneteau First 44,7 41
Beneteau First 47,7 46

Any comments guys?

Antonio

Guillermo

12-07-2006, 05:43 AM

Hi Guillermo - I guess that's with the pilothouse door shut and all the windows remaining intact? Do you think both these factors are a certainty if its rough enough to roll 360?
I guess that too. I'm not sure about the certainty, but we have to consider that to give a CE STIX number under the ISO 12217, boats must previously comply with watertightness as per ISO 12216. Relating the pilothouse door, this last only asks for it to comply with locking and securing exigencies, but to keep it shut when needed is a crew's decission. As a first approach, I have to believe in the honesty of the designer, the builder and the Notified Body involved in the boat's categorization. (Well, all of us, users, have to, haven't we? ;) )

With regard to the canting keel article, the 'villains of the piece' again seem to be excessive beam and inadequate engineering of the keel. Do you know of any canting keel boats that have remained inverted with their keels fully intact and the control systems still operating?
Good question. The answer is no, or at least I don't remember at this moment, but I'll search for that. On your side...do you? Also other people's sharing their knowledge on this would be nice.

Cheers.

Guillermo

12-07-2006, 06:04 AM

...Do we do the right without claiming more security to the ARC Head Office ?
Antonio, do they ask for a minimum STIX, Capsize Ratio, RORC's SSSN, or whatever?

Cheers.

Guillermo

12-07-2006, 08:10 AM

I am wondering if we could use the 'Capsize Length' as defined by Karl L. Kirkman in the paper 'On the effect of size - as related to capsize resistance' included as Appendix A at the 'Final Report of the Directors' on the Fastnet Race '79, to give us a clue to seaworthiness to be used in parallel to the STIX.

This 'Capsize Length' (Imperial units) is defined as follows:
Capsize length L' = L*((base B/B)^2 + (base C/C)^2)^.5 * I/base I

Where:
L = measured length (MHS)
Base B = L/4 + 2
B = measured beam
Base C = 2 ft (center of pressure above VCG)
C = 2 – CGTOT
CGTOT = center of gravity referred to DWL
I = moment of inertia
base I = 0.135*L^4.5

If we estimate moment of inertia I as Disp^1.744/35.5 (SNAME/USYRU Safety from Capsize Committee), using most usually available data, we may quickly get a (not MHS but STIX like data based) Capsize Length for any boat and then compare it with the STIX.

As STIX is somewhat also a corrected length, we may compare 'length versus length' and so have a comparative about how the two criteria categorize a particular boat. Could it be somekind of a 'correcting factor' to STIX?

Applying this to the 'Zara of Arran' classic boat I posted before (Post # 126 (http://boatdesign.net/forums/showpost.php?p=113285&postcount=126)), using L as 0.7*Lwl+0.3*Lh and based on the several estimatives for her, I find that the Capsize Length for this boat is 36.31 ft. It's STIX is barely 29.

The Final Report of the Directors upwards mentioned, proposed that the minimum AVS for a boat should be: AVS (min) = 160 - L' . In the case of 'Zara of Arran', this calls for an AVS (min) of 123.7 which in this boat's case is much lower than the real value, 152.

May we say, then, that 'Zara of Arran' in spite of having an STIX of 29 is an ocean going boat? Well, it fulfills all the requirements of the ORC regulations derived from the Fastnet Race reports: It has a Capsize Safety Factor (CSF) of 1.51 (well under 2), a Capsize Length over 30 and her AVS is much greater than the minimum required, so.....

I'll try to do this comparative for several boats and post here what I find. Perhaps somebody has already gone into this comparative and if so we all may save time. Anybody?

Guillermo

12-09-2006, 03:40 PM

Some estimated data for the A35 type of boat:
(Basic data taken from: http://www.mussetplaisance.com/Pdf/A35.pdf . I'm not sure about her displacement condition)

Length/Beam Ratio L/B = 2,78
Ballast/Disp Ratio W/Disp = 0,4
Displacement/Length Ratio D/L = 133,66
Sail Area/Disp. Ratio SA/D = 24,01
Velocity Ratio VR = 1,24
Capsize Safety Factor CSF = 2,22
Motion Comfort Ratio MCR = 16,67
Heft Ratio HF = 0,61
Roll Period T = 1,91 Sec
Roll Acceleration Acc = 0,25 G's
Stability Index SI = 0,54
Angle of Vanishing Stability AVS = 120 º
Dellenbaugh Angle DA = 22,42 º
Initial Metacentric height GMo = 1,74 M

Nice boat for coastal racing courses, but saying this is a bluewater family cruising boat would be quite enthousiastic in spite of her CE A categorization. And being a single ruddered boat with that wide beam, things will become interesting when strongly heeled or under chute in strong conditions.

Just to state a not mine opinion (I do not subscribe it as I do not have enough info, but tend to coincide):
"L'A-35 est un très bon bateau IRC, son palmares en 2006 est impressionant. C'est probablement le bateau parfait pour le Trophée Atlantique. Inversement, ce n'est peut être pas le candidat idéal pour l'Offshore. Sa forme de coque nécessitant une bonne partie de l'équipage à l'arrière dans la brise n'est pas vraiment commode pour des courses longues. Il n'est probablement pas stable au portant dans la brise."

Guillermo

12-16-2006, 07:20 AM

A quick look on two very close models from X-Yachts: The racer X-41 and the cruiser X-40

(Approximate numbers)

X-41 (Racing)
http://www.x-yachts.com/seeems/17834.asp

Beam/Length Ratio B/L = 3,07
Ballast/Disp Ratio W/Disp = 0,38
Displacement/Length Ratio D/L = 163,25
Sail Area/Disp. Ratio SA/D = 27,3
Velocity Ratio VR = 1,28
Capsize Safety Factor CSF = 1,91
Motion Comfort Ratio MCR = 24,22
Downflooding angle: Fd = 105 º
Angle of Vanishing Stability AVS = 121 º
Roll Period T = 2,55 Sec
Roll Acceleration Acc = 0,15 G's
Stability Index SI = 0,7
Heft Ratio HF = 0,85
Dellenbaugh Angle DA = 32,82
Initial Metacentric height GMo = 1,16 M
Righting Arm 10º RA10 = 0,2 M
Righting Arm 20º RA20 = 0,37 M
Righting Arm 30º RA30 = 0,49 M

X-40 (Cruising)
http://www.x-yachts.com/seeems/12235.asp

Beam/Length Ratio B/L = 2,94
Ballast/Disp Ratio W/Disp = 0,41
Displacement/Length Ratio D/L = 177,1
Sail Area/Disp. Ratio SA/D = 21,96
Velocity Ratio VR = 1,19
Capsize Safety Factor CSF = 1,93
Motion Comfort Ratio MCR = 25,03
Downflooding angle: Fd = 105 º
Angle of Vanishing Stability AVS = 121 º
Roll Period T = 2,57 Sec
Roll Acceleration Acc = 0,15 G's
Stability Index SI = 0,68
Heft Ratio HF = 0,86
Dellenbaugh Angle DA = 24,03
Initial Metacentric height GMo = 1,24 M
Righting Arm 10º RA10 = 0,21 M
Righting Arm 20º RA20 = 0,39 M
Righting Arm 30º RA30 = 0,53 M

Interesting to find out that the racing boat appears to be slightly slender (L/B) and less stiffier (GMo) than the cruising one (Although bigger mass influences T, making it slightly bigger for the cruising boat). Interesting also the diverging tendency showed by SI and Heft Ratio.

And now the new cruiser-racer J-122:
http://www.jboats.com/j122/j122dimensions.htm

Beam/Length Ratio B/L = 3,04
Ballast/Disp Ratio W/Disp = 0,36
Displacement/Length Ratio D/L = 168,89
Sail Area/Disp. Ratio SA/D = 23,09
Velocity Ratio VR = 1,21
Capsize Safety Factor CSF = 1,9
Motion Comfort Ratio MCR = 24,5
Downflooding angle: Fd = 105 º
Angle of Vanishing Stability AVS = 120 º
Roll Period T = 2,56 Sec
Roll Acceleration Acc = 0,15 G's
Stability Index SI = 0,71
Heft Ratio HF = 0,86
Dellenbaugh Angle DA = 28,29
Initial Metacentric height GMo = 1,14 M
Righting Arm 10º RA10 = 0,2 M
Righting Arm 20º RA20 = 0,36 M
Righting Arm 30º RA30 = 0,49 M

I like much more this tendency than the A-35 and the like one, from the cruising point of view. I would like to have a look to their real stability curves and know their STIXs. If someone has info on this, will be greatly appreciated.

Cheers.

Guillermo

12-17-2006, 03:54 AM

Let's make another comparative on STIX vs Capsize Length, both expressed in feet, following the idea in post 188.

Taking the RM1200 I posted at post 175 (http://www.boatdesign.net/forums/showpost.php?p=115943&postcount=175) we have for her:

Lh = 39.34 ft
Lwl = 37.47 ft
And from those we get:
Base Length Factor (in feet) = 38.09 ft

Now, asuming her downflooding angle is 100º, we have:

STIX (100) = 32.92 ft
Capsize Length L' = 22.57 ft

So we see that the Capsize Length is even smaller than her STIX in ft, which is already smaller than the Base Length.

This boat would have not been allowed for blue water racing under the ORC regulations, as her CSF is as high as 2.24, her Capsize Length is much lower than the minimum required of 30 ft and her 119º AVS is also lower than the 137.43º required by the ORC in this case.

This numbers need a more accurate study, as probably the real moment of inertia of a bulbed boat may significatively differ from the estimated by the formula I = Disp^1.744/35.5 used for the calculation of L'. I need to work on this.

Modern bulbed boats with their very low VCOG and high moment of inertia compared to their light weight, should probably qualify higher, both at ORC and STIX. I think we'd need to revise the way of estimating the moment of inertia for its use at the Capsize Length formula, and also a way of taking it into account for the STIX.

Guillermo

12-27-2006, 01:47 AM

Something basic but interesting for further discussions

Guillermo

01-08-2007, 12:42 PM

Someone (Antonio?) asked about Open 60's stability curves. The only clues I've found in internet about Open 60's stability showing some curves, are at Finot Group's pages:
http://www.finot.com/general/index_ang.htm

Interesting to compare it with the other I've previously posted:
http://www.yachting.org.au/site/yach...%20Pu~0008.pdf

Cheers.

CT 249

01-15-2007, 10:19 AM

Could we imagine an ARC to Europe with any designs of Beneteau in bad weather?

Do we do the right without claiming more security to the ARC Head Office ?

Do we need a "little Sidney-Hobart" during the ARC for having clear ideas about what is right and what no?

Any comments guys?

Antonio

Well, in the "big Sydney Hobart" we had (from memory) one death basically from wave impact; one death from drowning in an inversion (LPS about 116, I think); one death from head injury in a roll over; and the remaining 3 deaths from the sinking of an old heavy boat.

We also had severe damage from rolls to and S&S 34 and a Cole 43 (pre-IOR boats, long, slender and heavy);

a man overboard from a heavy 43 footer, saved only by the extremely lucky chance that a helicopter was only minutes away;

a steel cruiser hove down till it lost its liferaft (the cruising sailors on board had a raft equipped for 6 crew in a boat with a crew of 8, and the raft didn't fit the chocks);

a heavy canoe-stern cruiser sank;

a non IOR lightweight rolled with massive deck damage (later sank, I think)

two IMS racer/cruisers rolled with severe damage;

a 65 foot light/medium racer rolled with severe damage;

etc

Given the fact that the fleet was mainly composed of IOR boats or IMS racers or racer/cruisers, there seems to be little evidence that there were any "clear ideas about what is right". The heavyweights suffered by far the worst death toll and sinking rate, pro rata.

Three of the designs that rolled (the S&S 34, the Cole 43, and the Farr 40 IOR) have done round-the-world singlehanded passages around Cape Horn and the Cape of Good Hope. Similarly, another '98 competitor, the Brolga 33 Berrimella, was rolled and was dismasted with other damage on her return from the latest Hobart - after she had sailed around the world two-handed via the great Capes last year.

The fact is that designs that rolled with damage in Hobart '98 and while returning from Hobart 2006 have completed something like 7 solo or doublehanded circumnavigations via Cape Horn without significant damage. It therefore seems that saying that boats that failed in the '98 Hobart are unseaworthy is raising the bar ridiculously high. "Unseaworthy" designs rarely complete 3 or more singlehanded or doublehanded circumnavigations via the Southern Ocean without significant damage.

Similarly, it often seems to be ignored that we have had precious little experience about how "seaworthy" designs would have fared in such conditions, as they were not there in great numbers. Two of the few heavy cruisers that competed sank through construction problems and one was knocked down with minimal damage. A Swan 46 was rolled about 180.

Similarly, while hte '79 Fastnet report noted that smaller boats had many problems (although the smallest did better than the second-smallest) this has not been the case in any of the bad Hobarts, which surely may indicate the problem with making decisions based on such small statistical samples; the problem with Class IV in the '79 Fastnet may well have been that they were in the wrong place for the weather.

Of interest, I checked one submission to a conference held after the '98 Hobart. It had a chart showing the capsizes of boats int he NZ-Tonga event, the Hobart and the Fastnet. It said that heavy cruising boats were safer, without actually defining the type. The real eye-opener was that it said that only one heavy cruising boat had capsized in these races. It ignored the several rolls from pre-IOR boats of a type very similar to the renowned Contessa 32, used so often as an example of a superior boat.

This is clearly wrong; several traditional heavy cruisers rolled or otherwise got into trouble in the Tonga event (the only one in which they were not vastly outnumbered by lighter racing boats, which is one reason using the Hobart and Fastnet to attack lightweights seems flawed in some respects). There does seem to be a fair bit of poor research from the heavy brigade.

Guillermo

01-16-2007, 12:22 AM

....may indicate the problem with making decisions based on such small statistical samples...
Well, I agree and I don't. I think there has been quite a lot of investigation on the matter, done by scientifics (and not only) all around the world, based not only in real events, but also on tank testing. As I told in some other posts, I'm missing more accurate and complete statistics and studies from real life (like the Masuyama, Nakamura, Tatano and Takagi's one) based not only in catastrophic knockdowns, which by a matter of probability should be only the 'top of the iceberg' (Gauss bell), but in all kind of losts of control, course keeping instabilities, etc. These aspects have been repeatedly studied at tank tests, with quite clear results, but it would be very important to collect accurate data from real life. There are factors not measurable in tank tests, one of which is crews factor and their decission-making interference with results. Most interesting matter.
Cheers.

Guillermo

01-24-2007, 10:09 AM

Extracted from a 2003 report from Richard Slater to the Australian Yachting Federation:

"The use of STIX in Australia is limited at this time. Mainly because the highest level STIX (design category A) has the following parameters:
Wave height: up to approx 7 m significant (highest 1/3rd of waves)
Typical Beaufort wind force up to 10
Calculation wind speed (m/s) 28
When considering many Ocean Races include sailing in Southern Australia / Bass Straight these parameters seem low. One option that we have canvassed to RORC is the possibility that a design category can be set with the above variables increased."

Crag Cay

01-24-2007, 12:51 PM

I'm not sure what the problem is. As I understand, the only relevence of Design Category A to racing, is that the ISAF in OSR 2006 3.04.4 says that ISO 12217-2 Cats MAY be used to show compliance with the Race Organisers STIX requirement. But this would only be if the Race Organisers felt those STIX numbers were sufficient.

However, this OPTION comes after the REQUIREMENT (OSR 3.04.3) for Race Organisers or National Authorities to set the Minimum STIX Requirement at whatever level they feel appropriate for that race. Surely the Australians are at liberty to set a minimum STIX at whatever level they feel appropriate ? I'm sure I've seen races here (OSTAR ?) where the minimum STIX is higher than the minimum required for ISO Cat A.

Guillermo

01-26-2007, 02:26 AM

Paulo brought to my attention a mistake in RM 1200 data: Her AVS is indeed 119º and not 116º. My mistake comes from the scanning and digitizing of her Stability curve from PBO magazine: a distortion was produced, so the wrong angle. I'm sorry for that.

(See post 175 (http://boatdesign.net/forums/showpost.php?p=115943&postcount=175))

I did all the process again, and now my digitized curve is, I think, pretty close to the one at PBO (which may be, on its side yet distorted, absolutely). As Dfl (downflooding) angle is the only data missing to calculate her STIX, let's find out her various STIX at several Dfl angles:

100º ---- 33,521
120º ----- 36,423
130º ----- 36,423
Etc.

120º is very close to her AVS angle (119º)

From 120º up the FDF factor keeps constant at its maximum value of 1,25 and so STIX values over that downflooding angle remain the same, 36,423

AS we can see her STIX at 100º is now of 33,521 instead of 32,92 as calculated before (Not a huge difference, but a difference)

Paulo says he has been told RM 1200 STIX is 38,33 for the MSC (at this moment named MOC) condition, and 38,7 for MxSC (I understand this is the loaded condition. Nowadays MTL).

As STIX shall be taken as the lowest of all encountered values, I asume 38,33 as being its official STIX. The difference is now from 38,33 to 36,43 (almost two points).

To reach that value, I should:
-diminish her sail area from 86,67 m2 to 53,4 m2, which seems unrealistic.
- increase her MOC to 7720 mkg instead of the 6876 kg used.
- (taking 7800 kg as MOC, as published at PBO magazine, her STIX raises to 38,514, other values kept constant).
- use 7800 kg as MOC, and bring down Bwl to 3,73 m instead of my estimated 3,8

So this boat with a 120º downflooding angle, 3.73 m Bwl and a MOC of 7800 kg, may very well reach the informed 38,33 STIX value.

I have to recognize my numbers were not accurate and misleading, so I apologize to everybody, specially to Marc Lombard and RM boats.

I change my final statement in post 175 on this boat, to the following:

"An interesting boat, no doubt, with some interesting features. But, with that length/beam ratio, light displacement, high negative area at the GZ curve (32% of the positive), maximum negative GZ slightly bigger than the 50% of her maximum positive GZ, and maximum GZ at around 50º, this boat has no desirable stability characteristics, in my opinion, for an all around oceanic cruiser"

Cheers.

Guillermo

01-28-2007, 02:13 AM

The RM 1200's STIX figure, as well as the POGO 40's one (as per numbers posted at the Seaworthiness thread, see post 422 (http://boatdesign.net/forums/showpost.php?p=123180&postcount=422) there with all reserves of the case) are heavily dependant on their downflooding angle, which depends on the boat's beam as well as on flooding point height. So we realize here that, although STIX directly penalizes beam at FBD factor, it directly favours it at FDS and FDF ones trough the downflooding angle, one of the single elements that more heavily influences STIX by itself.

I would really want to know the RM 1200's downflooding angle used to calculate the 38,33 STIX figure. 120º is higher than her 119º AVS, which may be, absolutely, but I would like to check it. Well, in fact I would like to have access to the whole calculation, as per some doubts about the accuracy of some STIX related data given at the Seaworthiness thread. See post 436 (http://www.boatdesign.net/forums/showpost.php?p=123344&postcount=436)there.

About the influence of downflooding point height on STIX, see again post 87 (http://boatdesign.net/forums/showpost.php?p=111470&postcount=87) of this thread.

Cheers.

Guillermo

02-10-2007, 05:59 AM

More info on CE's RCD categorization of boats:
We've seen Multichine 28 (http://www.yachtdesign.com.br/02_ingles/plans/mc28/tech28-2.html) is said to be a Category A boat. Now I learn Nauticat 38 is a Category B boat! (http://www.nauticat.com/Default.aspx?id=436151&BoatId=7&ShowView=Specifications). May we that easily asume Multichine 28 is a more seaworthy boat than Nauticat 38? Is this surprising categorization related with Nauticat 38's STIX calculation or is there any other reason? Anyone knows?

Cheers

Guillermo

02-11-2007, 12:52 PM

Well, well, well....!
Yesterday I learnt POGO 40 has a delta factor within her STIX (Paulo dixit), because of its built in unsinkability (watertight subdivisions. I should have realized that by myself! I'm losing faculties...! ;) ). So to be able to compare its stability characteristics with those of other boats it's fair to take out this delta factor from the STIX number, or, to say it in other words, compare the rest of the STIX factors, not taking delta into account.

So taking out the 5 enters from what it seems to be POGO 40 Cruiser's MOC STIX of 41.3 (the one relevant to its categorization) we get a figure of 36.3 formed only by the geometry and weight related factors of STIX, this is LBS, FDL, FBD, FKR, FIR, FDS and FWM.

Surprisingly we find out now this figure is lower than the 38.33 of the RM 1200, which is a boat not unsinkable as far as I know, so its STIX being formed only by the beforementioned factors, and comparable to Beneteau 373's one. So, what is wrong here? STIX method...? POGO 40...? Me....? :)

About delta factor (which is not mathematically a factor, but an addend with a fixed value of 5 enters, whatever the boat if unsinkable under ISO 12217 and with positive lever arm at 90º), I think (And I have said this before in this thread) it would be interesting to take it out of the STIX figure to make different boats' STIXs more fairly comparable, and mention it as a separated bonus. Something like adding an U letter or the like to a 'not delta' STIX, or either to the standard STIX, just to make it clear its figure is influenced by delta.

Mikey

02-11-2007, 09:11 PM

it would be interesting to take it out of the STIX figure to make different boats' STIXs more fairly comparable, and mention it as a separated bonus. Something like adding an U letter or the like to a 'not delta' STIX, or either to the standard STIX, just to make it clear its figure is influenced by delta.

Guillermo, I agree with your suggestion, stability and seaworthiness should primarily be assessed as pre-event and secondarily as post-event. 36.3U would show a clearer picture than 41.3 and is the way this should be shown

Mikey

Man Overboard

02-11-2007, 09:43 PM

A portion of this post appears in the seaworthiness thread, but it also has relevance within this thread.

I don't think that eliminating "pre-event” and "post-event" circumstances is a proper methodology for evaluating seaworthiness. As Guillermo has pointed out, it has merit when comparing two boats, to evaluate other parameters, but the fact that the Pogo 40 has watertight compartments is a significant safety feature that can not go overlooked. It is indeed in keeping with safety features already implemented in the open 60 class boats, and is an example of how safety features that compliment a more extreme design can, and should go hand in hand. Just less than a month ago Mr. Greenwood out of New York has made the following comment:

Originally posted by DGreenwood:
Imagine a cruiser having to meet the buoyancy rules for example (water tight bulkheads). That right there would make them way too expensive.

Source, post # 29:
http://www.boatdesign.net/forums/showthread.php?t=15206&page=2

and now here we have an example of just that.

May I also call your attention to the fact that a boat rolling over is partly pre-event, and partially post-event; yet we don’t discount the post-event inversion as trite. No, indeed we attribute a greater necessity for the boat to self right. So if there is some other catastrophic event, say downloading, or a breach in the hull, I would think that not sinking should rank pretty high up on the seaworthiness scale; especially since it is one of the big complaints of the multihull proponents.

Guillermo

02-11-2007, 10:19 PM

I don't think that eliminating "pre-event” and "post-event" circumstances is a proper methodology for evaluating seaworthiness.
I totally agree, Tom. But what I'm proposing is to indicate things in separate, not to mix them in a single figure. Otherwise comparative may lead to confusion.
Cheers.

Guillermo

02-11-2007, 10:39 PM

Because of its interest and for the sake of this thread, let me quote Rolf Eliasson words on the developing of STIX, in Professional Boatbuilder Magazine:

"In late 1991 John Moon, then head of RORC's measurement office, presented the ISO TC 188 Stability working group the idea of rating boats by a stability numeral. He was encouraged by the convener of the working group, Andrew Blyth of Great Britain. Needless to say the RYA representative, Ken Kershaw, was very supportive. Nevertheless, the proposal was received with silence. Too new, too unknown, and too radical an approach for a stability assessment, was the general response. So the group continued to look for common ground on minimum downflooding and vanishing-stability angles. Every country had its own ideas, and every country had good statistics to prove that it was right. Stalemate.

It was impossible for the group of 20 to 30 people to agree on a common approach, so a subgroup was formed consisting of the originator John Moon, Professor Peter van Oossanen from the Netherlands, Gregoire Dolto from France, and me.

We were charged with developing the stability-numeral method and validating it so that consensus could be reached within the main working group. Ours was fruitful cooperation. Equations were tuned and calibrated, and the most important were checked against a giant database of existing boats. Finally we were ready to share the results with the larger ISO 12217-2 group. The response was: Good work, but we cannot use this as the only method to assess the stability of a sailing vessel. Neither was was there any consensus regarding the fixed limits of downflooding or vanishing-stability angle.

This meeting took place in 1996 in Vienna, and it was there that the STIX method was eventually agreed upon - provided additional requirements of minimum downflooding heights and angles, together with minimum vanishing-stability angles, were also taken into account, and more validation was done. Several years later, STIX has become a part of an international standard. It seems like an unnecessarily long time, but I can tell you that to come to a consensus with so many countries is no minor feat. Ask the United Nations."

Mikey

02-12-2007, 12:39 AM

I totally agree, Tom. But what I'm proposing is to indicate things in separate, not to mix them in a single figure. Otherwise comparative may lead to confusion. Cheers.

Two of the main business rules I work with every day are "keep things simple" and "don't spread important information around". The simpler, the clearer, the closer together important information is, the easier it is to pass on the whole message.

STIX 36.3U looks perfect to me :)

Mikey

fcfc

02-12-2007, 04:40 AM

Guillermo

02-12-2007, 01:56 PM

Two of the main business rules I work with every day are "keep things simple" and "don't spread important information around". The simpler, the clearer, the closer together important information is, the easier it is to pass on the whole message.

STIX 36.3U looks perfect to me :)

Mikey
It could also be 41.3U or 41.3*, or the like, to not diminish the attained STIX number for the boat, but clearly indicating the figure includes the effect of unsinkability. This would be particularly useful when comparing STIXs in a list.
Cheers.

Guillermo

02-12-2007, 02:16 PM

I know I will fuel Guillermo ideas, but there is strong differences between sailboats and powerboats in the ISO rules.

Most hard factor in powerboats is the required righting moment at 30° of 25 000 N.m for category A and 7 000 N.m for category B.

If you take a mini 6.5, I think most with STIX in category B due to unsinkability, remove the mast and put an engine :P It would not be in category B in powerboats, because it would not have enough rigthing moment at 30 °. An empty 1 T boat would need 70 cm GZ at 30°.

And worse for category A, the multichine 28, category A sailboat, would be only slightly above half of the required rigthing moment of the minimum category A powerboat.

And unsinkability do not help you in rigthing moment or wind/rolling criteria. It just help you to have a bigger cockpit, and only in category B and lower.
Requirements based in righting arms and areas under the dynamic stability curves for certain angles, as well as criterias for the effect of wind and waves, are widespreadly used for commercial boats regulations, including sailboats. That's another way to look at the thing, useful for professionals, but that kind of information uses to be not available for owners of recreational boats and I'm not sure if they will be really useful for them (except for a few knowledgeable people). Have a look at the interesting and comprehensive rules under development in Australia:
http://www.nmsc.gov.au/documents/NSCV_Subsection_6A_2nd.pdf

Cheers.

Mikey

02-12-2007, 09:34 PM

STIX is often used to determine how safe a boat is, if pre-event is a more important state to communicate then it should be 36.3U, if post-event is more important then 41.3U.

I would say that pre-event is more important. The U is more than enough to communicate to the guy up-side-down that - OK, it won't sink anyway :)

Mikey

Guillermo

02-13-2007, 03:25 PM

...Now I learn Nauticat 38 is a Category B boat! (http://www.nauticat.com/Default.aspx?id=436151&BoatId=7&ShowView=Specifications).
I wrote Nauticat to ask about this, and here the response:

"Hello Mr. Gefaell
The stability of the boat is more than enough for category A, but it is the side doors, which makes it extremely difficult to get it in category A, as those are considered as flooding openings.
I hope this explains the situation. The same thing with our Nauticat-331 and Nauticat-44.
best regards
NAUTICAT YACHTS OY
Veli Kärjä"

Here we have a decent builder and another STIX 'strange' situation. Thanks a lot Veli.

Mikey

02-13-2007, 07:59 PM

There we are... also the Nauticat 44 is a category B boat but Multichine 28 is a category A boat :(

Something is just not quite right here.

Mikey

fcfc

02-14-2007, 09:54 AM

Funny, this http://www.formenti-forsea.it/en/53.htm is in the same category as the nauticat 44.

This http://www.floatingneutrinos.com/son%20of%20town%20hall/Son%20of%20Town%20Hall.html is also an interesting "thing" to cross atlantic, too.

Guillermo

02-14-2007, 02:18 PM

Funny, this http://www.formenti-forsea.it/en/53.htm is in the same category as the nauticat 44.
There are several models of Ribs around there categorized as B. There is not an STIX calculation and number for them, but an specific norm: ISO 6185-4. But I'm interested to know how a 5.35 m length one is able to be B categorized, as there is not a norm usable for that under 8 m length, if I'm not wrong.

Most hard factor in powerboats is the required righting moment at 30° of 25 000 N.m for category A and 7 000 N.m for category B.

If you take a mini 6.5, I think most with STIX in category B due to unsinkability, remove the mast and put an engine It would not be in category B in powerboats, because it would not have enough rigthing moment at 30 °. An empty 1 T boat would need 70 cm GZ at 30°.
But a 3,5 tonnes one will only need 0,2 m. Weight, always weight...! :)

Cheers.

Guillermo

02-20-2007, 02:40 PM

Too busy these days to actively participate in the Forums.
Just a quick post to inform I have posted an improved release of the STIX spreadsheet calculator, available at the "Spreadsheet Library" (http://www.boatdesign.net/forums/downloads.php?do=file&id=36). I'll keep working on that (as time allows) to make it more complete and useful.
Cheers.

Guillermo

03-17-2007, 04:03 PM

Brian Trenhaille of Hawaii Marine has developed a very complete spreadsheet to estimate a lot of your sailing boat's characteristics. It doesn't calculate STIX, but a lot of other useful info.

http://hawaii-marine.com/templates/Products/ASail-e/description.htm

From there:
"This spreadsheet takes you input values for your sail boat and automatically calculates many of your sail boat's numerical characteristics (ratios, coefficients and parameters). Then this spreadsheet presents various target values allowing you to quickly check and compare your sailboat's characteristics with other similar successful sail boats.

There are several advantages and benefits to this calculative approach. Some of these advantages are listed below.

First, this method saves time. Many of computations are quickly generated behind the scenes on your input data. Also to modify, simply change a value in the spreadsheet and it will automatically and immediately recalculates all affected values.
bullet

Second, this approach provides clear and neat documentation.

Third this approach is cost effective because the calculative approach is already developed for you, research time is minimized to the familiarization of concepts when necessary and not to time consuming development activities.

Fourth, this template is kept simple, it contains no Excel macros and there is no Visual Basic code utilized in it's creation. Also advanced Excel features such "Goal Seek," "Solver" and "Scenarios" are not used.

Fifth, because this is a spreadsheet and not a program, the users can easily modify it to suit their particular needs."

Guillermo

04-28-2007, 08:16 PM

I like this 40 footer
http://www.nordship.dk/index.php?id=351&main=Yachts&menu=Nordship%20DS40&menuid=344

Specification here: http://www.nordship.dk/nordship/files/File/PDF/40_UK_Total_07-02-2006.pdf

Some estimated numbers for her:

Basic data from Yachting World and Nordship's site.

Overall Hull Length = 12,2 m
Length Waterline = 10,8 m
Flooded Buoyancy = (Y/N) N
Beam Waterline = 3,51 m
Beam = 3,9 m
Displacement MOC = 11100 kg (best guess)
Displacement Max = 12948 kg (best guess)
Height of CE above DWL = 7,52 m
Height of CLR below DWL = 0,8 m
Angle of vanishing stability = 140 deg
Downflooding angle = 120 deg (best guess)
GZ at downflooding angle = 0,25 m
GZ at 90 degrees = 0,67 m
Sail Area = 78 sqm (site) & 95,9 sqm (YW) -- I,J,P,E missing
Area to flooding (Agz) = 68 m.deg
Area to AVS = 70 m.deg

STIX factors and figure for MOC and 78 sqm SA:

Base Length Factor (LBS) = 11,267
Displacement Length Factor (FDL) = 1,040
Beam Displacement Factor (FBD) = 1,061
Knockdown Recovery Factor (FKR) = 1,435
Inversion Recovery Factor (FIR) = 1,186
Dynamic Stability Factor (FDS) = 1,231
Vaw (Not aplicable)
Wind Moment Factor (FWM) = 1,000
Downflooding Factor (FDF) = 1,250
Delta = 0

STIX = 54,984 (Wow!)
Note: Maybe this figure is some enters lower due to the 120º guess on downflooding angle. If it were 110º, STIX would be around 53 and around 49 if 100º.

Ratios related to 10500 kg lighship condition, 3700 kg ballast and 2 m keel. Figures in () are for full load:

Length/Beam Ratio L/B = 2,88 as: (0,7*LWL +0,3* LOA)/Bmax
Lwl/Bwl Ratio Lwl/Bwl = 3,08
Ballast/Disp Ratio W/Disp = 0,35 (0,29)
Displacement/Length Ratio D/L = 232,49 (around 280?)
Sail Area/Disp. Ratio SA/D = 16,53 (14,37)
Sail Area/Wetted surface SA/WS = 2,33 -- best guess for WS: 33,44 sqm
Power/ Disp. Ratio HP/D = 2,41 HP/ton (1,95)
'Hull speed' HSPD = 7,98 Kn
Potential Maximum Speed PMS = 9,15 Kn (8,1)
Velocity Ratio VR = 1,15 (1,02)
Efficient motoring speed (1.1 S/L) EMSPD = 6,55 Kn
Capsize Safety Factor CSF = 1,8 (1,68)
Motion Comfort Ratio MCR = 32,35 (39,90)
Heft Ratio HF = 1,1 (1,36)
Roll Period T = 3,67 Sec (4,41)
Roll Acceleration Acc = 0,08 G's (0,05)
Stability Index SI = 0,94 (1,13)

Something like a 10% more of sail area would have been nice to my taste, just to bring SA/D ratio to around 18 for lightship and 16 for full load, to make her more agile in light winds. STIX would still between 48 to 53 (depending on Dfl angle) which are yet very nice figures for this size of boat nowadays (Anyhow I would have not been discontent with present SA figure).

Vega

04-28-2007, 08:59 PM

Yes, it is a good boat. I have said that two years ago when the boat was released.

http://www.boatdesign.net/forums/showthread.php?p=121613&highlight=nordship+40#post121613

http://www.boatdesign.net/forums/showthread.php?p=114563&highlight=nordship+40#post114563

http://www.boatdesign.net/forums/showthread.php?p=82925&highlight=nordship+40#post82925

Guillermo

04-29-2007, 05:17 AM

OK. I'll buy this one and you buy the Pogo 40 :cool:

Guillermo

05-10-2007, 01:07 AM

Some interesting (estimated) numbers for CIGALE 14 (http://www.alubat.com/voilier%20alu%20cigale14.php):

Lightship (7000 kg)

Length/Beam Ratio L/B = 3,03
Lwl/Bwl Ratio = 3,33
Ballast/Disp Ratio W/Disp = 0,47
Displacement/Length Ratio D/L = 79,36
Sail Area/Disp. Ratio SA/D = 25,56
Sail Area/Wetted surface SA/WS = 2,23
Power/ Disp. Ratio HP/D = 3,26 HP/ton
Hull speed HSPD = 8,92 Kn
Potential Maximum Speed PMS = 11,16 Kn
Velocity Ratio VR = 1,25
Best motoring speed (1.1) CSPD = 7,32 Kn
Capsize Safety Factor CSF = 2,37
Motion Comfort Ratio MCR = 14,65
Heft Ratio HF = 0,48
Roll Period T = 1,86 Sec
Roll Acceleration Acc = 0,36 G's
Stability Index SI = 0,41
Angle of Vanishing Stability AVS = 116 º

Full load (9300 kg?) 6 pax. No water ballast considered.

Ballast/Disp Ratio W/Disp = 0,35
Displacement/Length Ratio D/L = 105,43
Sail Area/Disp. Ratio SA/D = 21,15
Sail Area/Wetted surface SA/WS = 2,13
Power/ Disp. Ratio HP/D = 2,45 HP/ton
Hull speed HSPD = 8,92 Kn
Potential Maximum Speed PMS = 10,4 Kn
Velocity Ratio VR = 1,17
Best motoring speed (1.1) CSPD = 7,32 Kn
Capsize Safety Factor CSF = 2,16
Motion Comfort Ratio MCR = 19,46
Heft Ratio HF = 0,64
Roll Period T = 2,38 Sec
Roll Acceleration Acc = 0,22 G's
Stability Index SI = 0,53
Angle of Vanishing Stability AVS = 114 º

More info at: http://www.northseamaritime.com/Page/ALUc14.htm

A pity not having a GZ curve for this boat.

Guillermo

05-13-2007, 02:07 PM

And now an excellent design from Heyman Yacht Design (http://www.heymanyachtdesign.com/), in Sweden, very much of my content! :)

One of the boats I'd buy or built, if only I could! :cool:
(SA sems somewhat low to me, but her ketch rig allows for an extra mizzen staysail)

Some preliminary numbers for her, asuming the stated displacement of 36 tonnes is for the MOC, and downflooding occurs at 115º.
Cp is asumed as 0,56 and Cwp as 0,7

ATOA 64
Loa = 22,30 m
Lh = 19,50 m
Lwl = 17,32 m
Bmax = 5,40 m
Bwl = 4,86 m
Draught T = 1,60 m
Body draught Tc = 0,95 m
Disp = 36000 kg (Asumed to be MOC)
Ballast = 10000 kg
Sail area = 146,4 m2 (estimated measuring I, J, P...etc, from drawings)
Power = 140 KW
Heeling Arm = 8,97 m
WS Appendages = 13,18 m2
WS Hull = 65,89 m2
Wetted Surface = 79,07 m2

Length/Beam Ratio L/B = 3,33
Lwl/Bwl Ratio Lw/Bw = 3,56
Ballast/Disp Ratio W/Disp = 0,28
Displacement/Length Ratio D/L = 193,26
Sail Area/Disp. Ratio SA/D = 13,64
Sail Area/Wetted surface SA/WS = 1,85
SA (metric)/ Power (Imp.) SA/HP = 0,77
Power/ Disp. Ratio HP/D = 2,40 HP/ton
Hull speed HSPD = 10,10 Kn
Potential Maximum Speed PMS = 9,8 Kn
Velocity Ratio VR = 0,97
Best motoring speed (1.1) CSPD = 8,29 Kn
Capsize Safety Factor CSF = 1,65
Motion Comfort Ratio MCR = 44,87
Heft Ratio HF = 1,24
Righting Moment/Beam RMB = 0,8
Roll Period T = 5,21 Sec
Roll Acceleration Acc = 0,06 G's
Stability Index SI = 0,97

Displacement MOC = 36000 kg
Displacement Max = 42295 kg
Height of CE above DWL = 8,33 m
Height of CLR below DWL = 0,64 m
Angle of vanishing stability = 132 deg
Downflooding angle = 115 deg (best guess)
GZ at downflooding angle = 0,24 m
GZ at 90 degrees = 0,61 m
Sail Area = 146,4 sq.m
Area to flooding (Agz) = 55,48 m.deg
Area to AVS = 58,67 m.deg

Base Length Factor (LBS) = 18,047
Displacement Length Factor (FDL) = 1,067
Beam Displacement Factor (FBD) = 1,061
Knockdown Recovery Factor (FKR) = 1,500
Inversion Recovery Factor (FIR) = 1,288
Dynamic Stability Factor (FDS) = 0,795
Vaw = Not aplicable
Wind Moment Factor (FWM) = 1,000
Downflooding Factor (FDF) = 1,250

Delta = 5

STIX = 75,140

I would like to clarify the displacement and downflooding angle doubts. Somebody?
More info at:
http://www.atoa64.com/

Cheers.

Vega

06-02-2007, 07:24 PM

Some interesting (estimated) numbers for CIGALE 14 (http://www.alubat.com/voilier%20alu%20cigale14.php):

Lightship (7000 kg)

Angle of Vanishing Stability AVS = 116 º

The Msc AVS = 121º

Guillermo

06-02-2007, 07:51 PM

Excellent! Do you have the corresponding GZ curve?

Guillermo

08-29-2007, 04:33 PM

Coming back to the very initial purpose of this thread:
From a Dave Gerr's article at the Westlawn Institute Magazine's September 2007 issue:
"Because complying with the STIX under ISO is now the law in Europe, there is a tendency to interpret STIX as a good indicator of seaworthy stability in the U.S. I personally don't believe that STIX is all that a reliable indicator. Nevertheless the STIX number is a reasonable marker, but it is not as reliable -in my opinion- as simply applying the basic concepts above (he's referring to several of the 'old' ratios and parameters) along with one or two others involving dynamic stability...for really accurate results by designers"
http://www.westlawn.edu/news/WestlawnMasthead03_Sept07.pdf

(Italics are mine. Thanks a lot, Perry!)

YachtManuals

10-09-2007, 11:16 AM

I will post two images that explain the differences in dynamic stability and in the RM curves between beamy boats relying more on form stability and narrow boats, reeling more on Ballast.

I have seen this mistaken argument in several places. In fact any object floating on the inclined surface of a wave is accellerated sideways (in the direction on wave travel) so that apparent gravity is perpendicular to the surface of the water. The experiment would show that a pendelum suspended from anything floating on waves will always point straight down to the "deck" of the object. This means that deep keels and wide hulls both "heal" the same amount on the side of waves (assuming only the wave action). This can also be explained by the motion of a water particle on the surface of waves: they describe a circular motion. Otherwise the water on the wave surface would be rushing down to the bottom of the trough. In fact the water on the surface is perfectly happy to stay put, because it experiences the force of gravity as always pointing down perpendicular to the SURFACE of the wave, just like the vessel.

Vega

10-09-2007, 12:50 PM

I have seen this mistaken argument in several places. In fact any object floating on the inclined surface of a wave is accellerated sideways (in the direction on wave travel) so that apparent gravity is perpendicular to the surface of the water. The experiment would show that a pendelum suspended from anything floating on waves will always point straight down to the "deck" of the object. This means that deep keels and wide hulls both "heal" the same amount on the side of waves (assuming only the wave action). This can also be explained by the motion of a water particle on the surface of waves: they describe a circular motion. Otherwise the water on the wave surface would be rushing down to the bottom of the trough. In fact the water on the surface is perfectly happy to stay put, because it experiences the force of gravity as always pointing down perpendicular to the SURFACE of the wave, just like the vessel.

Yes, I had posted an image that shows otherwise. That image belongs to a presentation on boat stability by Professor Paul Miller (D. Eng.P.E.). He is the Professor of Naval Architecture at the United States Naval Academy.

Here we have that image again:

Guillermo

10-09-2007, 05:24 PM

From Marchaj's "Seaworthiness, the forgotten factor"

Man Overboard

10-09-2007, 08:08 PM

YachtManuals :
In fact any object floating on the inclined surface of a wave is accellerated sideways (in the direction on wave travel) so that apparent gravity is perpendicular to the surface of the water.

This is not necessarily true. An object floating on the surface does not respond the same as a particle of water immersed within the orbital flow of a wave pattern. We often explain wave motion by the circular motion of water particles; I believe it is more instructive to view waves as an orbital energy flow(s) through the surface of a body of water. This energy flow passes through the water in a rotation manner, and in doing so, acts upon water particles in suspension. Each particle of water moves in a direction that is a result of two components of acceleration: ‘g’ acceleration do to gravity, and ‘a’ centrifugal acceleration.

Centrifugal acceleration can be shown by the equation below_

The source of rotational energy flow is due to the fact that the energy flow uses water as a vehicle for propagation. Energy in effect passes from one particle of water to the next (very quickly) and in doing so imparts motion. That motion is resisted by gravity, and viscosity. Because there is less resistance do to viscosity at the very surface, than deeper within the water column directly below the orbit, the water moves more readily, and establishes a rotational flow. This rotational flow increases in magnitude as long as it is being energized by air flow across the surface. It should be mentioned that the gravity component both de-accelerates, and accelerates the water particles depending where they are in the rotational energy field. It is much easer, and more efficient for the energy to pass to adjacent water particles of microscopic size than to pass to large floating objects. In addition, floating objects have various other forces acting on them, especially a boat. A deeply immersed boat such as the example posted by Guillermo may be subject to subsurface energy propagation. (Sub-surface orbital flow) Although there is orbital forces imparted to the vessel, there may also be other forces that have an over riding influence: healing forces, components of lift from the keel, rudder, and sails, etc. Gravitational and buoyancy forces on the boat as a whole may have a much great magnitude of force than the energy absorbed by angular velocity. It should be noted, in the case of sailboats, the components of lift from the sails, rudder, and keel also impart rotational energy fields which disturb and alter wave patterns. A moving sailboat creates gyroscopic energy forces that resist and dampens the impact of waves. A fast boat can be more stable than a slow boat. (but not always)

MikeJohns

10-09-2007, 09:03 PM

……………..In fact any object floating on the inclined surface of a wave is accellerated (sic) sideways (in the direction on wave travel) so that apparent gravity is perpendicular to the surface of the water............

Any attempt to simplify vessel-wave interaction to such trivial “Fact” is not a sensible approach. Also I would certainly question the source of this mis-information.

Guillermo

10-27-2007, 08:17 PM

Another new light kid in the block, with an strange categorization.

Sun Odissey 36i is said to be a Category A boat (So STIX >= 32), but with the posted info I cannot get more than a 26,67 figure for STIX, even assuming downflooding angle coincides with AVS (+/- 123º). Minimum AVS for this boat to qualify for A category = 117,6º

Stated displacement of 5725 kg is for lightship condition :mad: so I'm estimating a MOC of 6193 kg and I'm assuming posted curve is for that load condition. Considered keel is the standard 1,94 m one.

Even so, I get this:

Base Length Factor (LBS) = 10,207
Displacement Length Factor (FDL) = 0,971
Beam Displacement Factor (FBD) = 1,061
Knockdown Recovery Factor (FKR) = 1,056
Inversion Recovery Factor (FIR) = 1,015
Dynamic Stability Factor (FDS) = 0,574 (because of the poor GZ curve)
Vaw Not aplicable
Wind Moment Factor (FWM) = 1,000
Downflooding Factor (FDF) = 1,250

Delta = 0

STIX = 26,667

DESIGN CATEGORY B

How the hell they get a STIX of 32 or higher...? Do the posted GZ curve correspond to MOC? :confused:

Once again: It would be very nice if boatbuilders and magazines decide to provide more complete and clear info on stability.

And now here its 'old ratios'

Length/Beam Ratio L/B = 2,83
Lwl/Bwl Ratio Lwl/Bwl = 3,05
Ballast/Disp Ratio W/Disp = 0,25
Displacement/Length Ratio D/L = 181,30
Sail Area/Disp. Ratio SA/D = 17,39
Capsize Safety Factor CSF = 1,97
Motion Comfort Ratio MCR = 23,51
Heft Ratio HF = 0,86
Roll Acceleration Acc = 0,12 G's
Stability Index SI = 0,77

Vega

10-27-2007, 09:07 PM

Another new light kid in the block with an strange categorization.

Sun Odissey 36i is said to be a Category A boat (So STIX >= 32), but with the posted info I cannot get more than a 26,67 figure for STIX, even assuming downflooding angle coincides with AVS (+/- 123º). Minimum AVS for this boat to qualify for A category = 117,6º

Stated displacement of 5725 kg is for lightship condition :mad: so I'm estimating a MOC of 6193 kg and I'm assuming posted curve is for that load condition. Considered keel is the standard 1,94 m one.

.....

How the hell they get a STIX of 32 or higher...? Do the posted GZ curve correspond to MOC? :confused:

Once again: It would be very nice if boatbuilders and magazines decide to provide more complete and clear info on stability.

It looks to me a nice boat with a good stability curve.

If you ask Jeanneau, or even any Jeanneau dealer they would provide you with information on boat stability, in lightship and loaded condition.

It is obvious that the magazine as messed out with that curve (it is not the first time). I believe Jeanneau provided a correct one.
You should know that boat, with those characteristics (beamy, with a bulb and that ballast) could not have a Max GZ lower than 0.4m. I believe that it is a RM curve and that where is 0.4 should be 4.

Of course I can ask Jeanneau for the correct curve, but so can you;) .

Guillermo

10-28-2007, 02:01 AM

The GZ curve could very well be that one, precisely due to the beam, low ballast/displacement ratio, high freeboard and upwards volumes. But I'll ask them and PBO as you suggest.

Cheers.

Vega

10-28-2007, 03:55 PM

The GZ curve could very well be that one, precisely due to the beam, ... But I'll ask them and PBO as you suggest.

Beam increases form stability and therefore increases MaxGZ and MAXRM. Why do you think Open 60's and Class 40 are boats with large transoms, or as you like to call them beamy boats?
Take a look at the MaxGZ of a cat...it's huge and all form stability (beam).

The problem with large transom boats is not MaxGZ, but AVS and inverted stability. The Jeanneau 36i comes out with fling colors, with a reasonably good inverted stability and with an AVS (125º) slightly above average for a modern boat.

Look at this RM curve. Again the magazine messed up in several ways:D . They call it a GZ curve and the units.... well, but I hope you can understand it. It is of a powerful and fast boat, but this time with a very low AVS (109º) and a big inverted stability.

I believe you should focus on boats like these.:) (it's a Glamorous and beautiful new model and I like the design, with the exception of the stability curve:P )

Guillermo

10-29-2007, 02:47 AM

I'll answer you when I get the info back from Jeanneaou or PBO.

Vega

10-30-2007, 09:18 PM

The GZ curve could very well be that one, precisely due to the beam, low ballast/displacement ratio, high freeboard and upwards volumes. But I'll ask them and PBO as you suggest.
…..

I'll answer you when I get the info back from Jeanneaou or PBO.

Well, if you insist, but I am absolutely sure that 0.39 is not the MaxGZ value. The Max GZ of this kind of boats (jeanneau 36i) lies between 0.6 and 0.8. Most common value is a little bit over 0.7.

A Max GZ of 0.39 for the Jeanneau 36i (as it is on that curb you have posted) is inevitably a big nonsense.

Assuming that curb (the one you posted for the Jeanneau) is a RM curve I will post a comparison between the RM curves of the Jeanneau 36i, the Bavaria 36 and the Halberg-Rassy 342.

The Bavaria is the lightest boat, with about 5T for a ballast of 1340kg, 3.59m beam and a draft of 1.90.
The Halberg-Rassy weights 5.3T for a ballast of 1950kg, a 3.42 beam and a draft of 1.82.
The Jeanneau 36i weight 5.7T for a ballast of 1571kg, a 3.59 beam a draft of 1.95 and is the only one with a bulb.

By the way, the Bavaria MaxGZ is around 0.73 and the Halberg-Rassy MaxGZ is around 0.7.

For the Bavaria curb I will consider the one that doesn’t consider the influence of the cabin. If that influence is considered the AVS jumps to 131º and the inverted stability is a lot smaller.

Vega

10-31-2007, 06:19 PM

Well, I have not found out that curve, but I have found out the MaxRM value for the Jeanneau 36i: 3,9Txm, the same max value on that curve you have posted (0.39). With the MaxRM and the boat displacement you can calculate the MaxGZ;)

Vega

11-01-2007, 12:50 PM

I believe that the Puzzle is almost complete.

I have found another published stability curve for the Jeanneau 36I. This one was published in the June edition of Yachting Monthly.

I believe that this one, published as a GZ is also a RM curve.

At least on this one they didn’t change the decimals on the numbers. Can someone explain to me what is the meaning and the units of these figures (from the curve)??? :

1000.000, 2000.000, 3000.000 and so on.

I believe that these numbers refer to the RM curve, the unit is kg and they have 3 decimals.

If this is correct then we have here for the MaxRM 3200kgxm (3.2Txm) a smaller value than the MaxRM from the curve posted by Guillermo (3.9Txm). The AVS is also different, in this curve the AVS is 130º and on the other one 125º.

These differences are consistent, for this type of boat, with the differences between a RM curve in Max load sailing condition (curve posted by Guillermo) and a RM curve for the same boat in Min. load sailing condition (this one). Bigger RM and smaller AVS on Max load condition and Smaller RM and bigger AVS on Min Sailing Condition.

This would make this boat even a safer boat. I had thought that the curve posted by Guillermo was the Min sailing condition curve and that the 125º AVS was for that condition.
After all, the boat’s AVS for Min.Sailing condition is 130º and that is not good, is very good for this type of boats. There are few modern boats of this type that have a 125ºAVS in Max load condition.

What do you say, Guillermo?

Guillermo

11-02-2007, 02:32 AM

Vega

11-02-2007, 04:26 PM

I say we have to wait for an answer from PBO/Jeanneau/Marc Lombard (I've written to all of them).
Perhaps you're right and curve is a RM one, but as PBO's tested version is the shoal draught one and posted info is not clear enough, we'd better wait.

I have received the stability curves from Jeanneau. They seem to agree with me that RM curves are more appropriated to judge the boat stability:P , because they only have sent me RM curves:).

It looks that I was right.

The curve posted by you and published by PBO magazine is a RM curve from the GTE version (draft 1.94) with the boat in MaxSail condition. The curve published by Yachting Monthly and posted by me it is a RM curve with the boat in MinSailing Condition (the MinSailingcondition curve for the two different draft versions is identical).

Guillermo

11-03-2007, 02:52 AM

It seems you have a nice relationship with Jeanneau, as I got nothing from them yet (nor from PBO or Marc Lombard). You got that info even in the middle of the 1st of May 'bridge'....! Unbelivable :!: :confused:

You now may realize one the hazards of releasing RM curves instead of GZ ones: As the ISO norms use the GZ curves, even specialized and reputed magazines as YM and PBO go for the wrong. :(

(By the way: Your last posted curve seems to be also wrongly displaying units at the ordinates axis. Those cannot be mt)

Surprising to know the MLC gives a lower STIX than the MOC. Uses to be the contrary. I'll check the STIX numbers for your posted curves, when I get trustable data on considered displacements and downflooding angles. Can you provide that info?

Guillermo

11-03-2007, 04:51 AM

As per a very first estimative, asuming MOC displacement as 6055 kg and Dfl angle of 120º, I get an STIX of around 34-35 which makes more sense.

Maximum GZ for that asumed load condition is around 0,54m. If the PBO stated figure of 5725 kg is the real MOC, variations are not very great and GZ goes to around 0,58m.

I still want to know what the curve for the shoal draught version is.

Vega

11-03-2007, 06:57 PM

It seems you have a nice relationship with Jeanneau, as I got nothing from them yet (nor from PBO or Marc Lombard). You got that info even in the middle of the 1st of May 'bridge'....! Unbelivable :!: :confused:

You seem doubtful:rolleyes: but that’s easy to understand.

I have emailed them your post (link) and said that a Naval Engineer on a reputable boat internet forum had raised doubts about Jeanneau 36i stability.

I have pointed out that your analysis was based on a RM curve that had been published by PBO as a GZ curve. I have said that the MaxRM values taken as MaxGZ values would be ridiculously low values that, if taken seriously, would give a very bad impression of the boat, as it was the case.

I suggested them that they should demand a correction of the data published on PBO and Yachting Monthly and asked them to send me correct information on the boat stability.

I have e-mailed them on 1/11 at 15.00pm and I received a reply on 2/11 at 8.23 am.

I have also e-mailed PBO and Yachting Monthly, pointing out the mistake. The e-mail was sent on 1/11 at 15.30pm. They have replied to me on 2/11 at 9.52 and 10.11 am.

I believe responsible people get worried when wrong information that denigrates a boat is published, in magazines or in reputable internet sites.

You now may realize one the hazards of releasing RM curves instead of GZ ones: As the ISO norms use the GZ curves, even specialized and reputed magazines as YM and PBO go for the wrong. :(

I suppose that explains also why PBO also changed the decimals on that graph, from 1000 to 0.1, 2000 to 0.2 and so on:rolleyes: .

About RM curve versus GZ curve, we are talking about giving to the public information on boat stability and no more.

About this the words of Angermark Marin (the Architect of the Malos) are paradigmatic:

"When we talk to "ordinary" yachtsmen, we frequently notice that it is very easy to misunderstand the meaning of the usually published stability curve that indicates the righting lever ( G-Z ). This curve alone is no measure of a yacht´s real stability.

To illustrate this statement we have prepared stability data for three different boats, and it is very common that the G-Z curves as interpreted as indicating that all 3 yachts have roughly the same capacity to resist a capsize. In fact it is the curve of righting moment that illustrates this capacity. Every wave contains a certain amount of energy en every vessel requires a certain amount of energy to be turned over. The energy required to capsize a ship is represented by the area of curve above the baseline, and energy needed to return it to an upright position is represented by the area below the baseline. NOTE: This is only valid for the curve representing the righting moment, NOT the G-Z curve.

Thus we can see that it takes more than 4 times more energy to overturn the MALÖ 43 as the 33 footer. To return the MALÖ 43 it takes a wave containing 1/9 of the energy required to turn it over.

A much better assessment of the real stability is thus to compare the curves of righting moment… "

http://www.maloyachts.se/YACHTS/Stability/tabid/134/Default.aspx

http://www.maloyachts.se/LinkClick.aspx?fileticket=hzHfm%2fXKzyc%3d&tabid=134&mid=723

(By the way: Your last posted curve seems to be also wrongly displaying units at the ordinates axis. Those cannot be mt)

I believe “mt” stands for moment?

If this is the case I don’t understand what you mean. The units are clear, they refer to Kgf*m.

Guillermo

11-03-2007, 08:20 PM

Oh, Vega, Vega, savior knight of widows, orphans, boatyards and the like...! How I envy the strength of your arm and mighty sword...! :D

...and said that a Naval Engineer on a reputable boat internet forum had raised doubts about Jeanneau 36i stability.
You should have humbly stated: a "well reputed Ingeniero Naval...", as it is the case....:D

On top of that I don't remember to have risen doubts on the Jeanneau 36i stability, only on the quality of the provided info. In my country we have a word for your attitude: "torticerismo" (do me a favour and look for a translation, please :) )

...About this the words of Angermark Marin (the Architect of the Malos)...
Yes, you have posted about mr. Marin's opinion before. It seems to be one of your favourite 'strong anchors'. Of course his opinion is absolutely respectable and useful in certain cases, but I've told you: daily practice in naval architecture is rather to use GZ curves to assess a vessel's stability, precisely because their independence on size. I can swore this to you on the graves of my ancestors, if you don't believe me.....:)

On top of this, I think if a layman is able to interpret a RM curve, he will easily understand also how to get the moment from the GZ one when needed. To understand a RM curve, first we have to understand what GZ is (As you do :) )

I don't understand why you refuse to admit a different (and well supported) opinion to yours is possible and useful, my boy. Is it because you really don't understand this position, or just because you need to reinforce your personality trying to piss me off all the time? :)

And here it is me, giving you 15 positive rep points, when I think your collaboration is positive (post 235), in spite of your patronizing words in previous posts (I hope you can understand this, and the like...). Am I not a perfect idiot? :( :D

Cheers :)

Vega

11-04-2007, 06:05 PM

Quote:
Originally Posted by Vega
..".and said that a Naval Engineer on a reputable boat internet forum had raised doubts about Jeanneau 36i stability".

Guillermo:
.... I don't remember to have risen doubts on the Jeanneau 36i’s stability, only on the quality of the provided info. In my country we have a word for your attitude: "torticerismo" (do me a favour and look for a translation, :) please :) )

If you chose to insult a forum member, please do so in a language that everybody understands, do it in English.

It is obvious that you have a memory problem. You have said on post 230 :

Another new light kid in the block, with an strange categorization.

Sun Odissey 36i is said to be a Category A boat (So STIX >= 32),

You made a statement: "The boat has a Strange categorization "(Category A) and you have said : “is said to be a Category A boat”.

If the boat is strangely classified as a Category A boat, it seems clear to me that you are raising doubts about the fulfillement of the stability requirements needed do classify the boat in the A class, therefore you are rising doubts about the boat’s stability.

You know very well that this is a boat certified as a Class A boat. When you say : "IS SAID”, instead of IS A CATEGORY A, you are implying doubts about the correction of that classification.

If you have any doubts about the boat’s stability and its requirements to be classified as a class A boat you should have asked Jeanneau information on the boat’s stability before stating that the “Boat has a strange categorization”.

Once again: It would be very nice if boatbuilders ....decide to provide more complete and clear info on stability.

Jeanneau is one of boat manufacturers that provides very clear information about the performance and stability of their boats.

Because I was personally interested in the 39i and 42i, I have asked them information on those boats (months ago) and I have received very complete and clear information about them, including different RM curves and different performance polars (according to different drafts, different masts, different sails).

…. I get an STIX of around 34-35 which makes more sense.

Yes I agree, you are making more sense. This means that your previous statements about the “strange categorization” of the boat and about the “26,667 STIX - DESIGN CATEGORY B "makes no sense?

If you really are interested in the boat and want to know the STIX numbers why don’t you ask Jeanneau instead of posting STIX numbers that are most of the time different from the certified and correct figures?

That doesn’t seem to me a correct approach to analyze a boat. You should not post incorrect data neither calculate STIX numbers or Stability curves that are based on insufficient or incorrect information.

Basing a boat analysis on this kind of “material” can lead to gross error of judgment and bring unjustified prejudice over a given boat. This will affect the boat credibility and can contribute in some extend to a lesser commercial value.

If you were not a "well reputed Ingeniero Naval..., as it is the case” (as you consider yourself), posting on a reputable Design Forum, this could have no meaning. As it is, a manufacturer that sees the image of his boats degraded this way, by a reputable Naval Engineer, can rightly feel that a lawsuit is appropriated to bring justice to the wrongdoing.

I believe that if this is the case, it will not involve you, but the forum that has permitted that you repeatedly post incorrect data on boats and base boat analysis over incorrect information.

Even if a judicial problem never occurs, it is just plain wrong to post boat stability analysis that are based not on the boat’s own characteristics (STIX, Stability curves, Displacement in Min. Sailing Condition, Displacement in Max sailing condition and Downflooding angle) but on ones that are estimated by you and that in many cases are different from the real data.

Wrong data = wrong analysis.

I still want to know what the curve for the shoal draught version is.

You don’t need to ask in bold:) , you have only to ask ;) (provided by Jeanneau).

They have sent me also curves that take into account different types of masts (furling and classic) and polars of the boat speed. If someone is interested on the 36i and on this information say so, and I will post it.

Guillermo

11-05-2007, 05:08 PM

...Am I not a perfect idiot?
Yes! A perfect idiot....

Guillermo

11-11-2007, 11:44 AM

I've visited the Jeanneau's stand at the Barcelona Boat Show and had a look at the SO 36i. The exibited model had a nice keel with a conspicuosus bulb. I'll post some images tomorrow.

As probably her MLC with 8 people is bigger than 1.15*MOC, I've estimated what the STIX for this last condition could be (asuming a MLC of 8110 kg) and I come to a figure under 32 (!!!). If this is so, then the boat categorization should be rather B, instead of A, as it is mandatory to choose the lesser of the two values.

As I'm probably wrong, I would be very interested in knowing how her STIX numbers were calculated. I hope Jeanneau or Lombard will answer my mails some day, or either post here the proper info by themselves, not through well intentioned but not sufficiently informed and somewhat naive intermediaries.

Cheers.

Vega

11-11-2007, 02:07 PM

As probably her MLC with 8 people is bigger than 1.15*MOC, I've estimated what the STIX for this last condition could be (asuming a MLC of 8110 kg) and I come to a figure under 32 (!!!). If this is so, then the boat categorization should be rather B, instead of A, as it is mandatory to choose the lesser of the two values.

As I'm probably wrong, I would be very interested in knowing how her STIX numbers were calculated. I hope Jeanneau or Lombard will answer my mails some day, or either post here the proper info by themselves, not through well intentioned but not sufficiently informed and somewhat naive intermediaries.

Cheers.

I think you are wrong, otherwise the boat would not have been certified as a class A boat.

I understand that you wish to know where you failed, but saying "and I come to a figure under 32 (!!!). If this is so, then the boat categorization should be rather B" ...makes no sense, because if it were the case, the boat would not have been certified as a Class A boat, or Marc Lombard would have made a mistake in his calculations, or worse, had falsified them..

I don't think you should cast doubt about the boat stability unless you can demonstrate that Marc Lombard’s calculations are wrong. And if so, you should complain to the proper authorities.

Guillermo

11-11-2007, 04:46 PM

I'm not doubting about the boat's stability, nor designer's nor nobody's calculations or assessments. You're the one saying that. I'm just curious, trying to learn.

I want to make it very clear that I suspect absolutely nothing in this case, as Jeanneau is a well reputed and respected manufacturer, not in needing of doing this kind of things, but now that you bring the issue up to light, I think you would be surprised to know all the tricks and loopholes (when not plain lies, sometimes) used to qualify boats under the RCD, specially when moving in border zones, my naive friend.

Not to talk about the total lack of knowledge of the ISO rules many small boatbuilders have, who anyway riskly sign their boats' Conformity Certificates. They just do not know what they are certifying at all. Believe me.

On top of personally dealing with such matters in my everyday's professional life, I've just had recently the opportunity of knowing about the inspecting action of the authorities (DGMM) at this year's Barcelona Show, regarding such tricks and loopholes, because of that poor auto-control and loose attitude of some boatbuilders and unluckily even of some notified bodies' surveyors.

Several of our present clients, who were exhibiting boats at the Show, told us how right we were when we refused to hand over to their pressure on certain qualification demands (refusals that even have brought us to painfully lost clients in certain cases), because they passed unharmed through inspections, which not all of the exhibitors did.

Felix qui potuit rerunt cognoscere causas....

Cheers.

Pericles

11-12-2007, 03:13 AM

A classical education Guillermo?

Happy he, who could understand the causes of things.

Virgil Georgics: Book 2, Line 490

Vega is a bit of a pain in the bum, without much of a sense of humour. I had a look at his background and viewed his pretty pictures. He does not give any personal information as to age, career, qualifications or details about boats he has built. There is a vacuum there, where there should be a plenum. He talks in generalities without citing his authority, For example, he has a tendency to state the obvious as if it is a nugget of gold that only he has discovered, and then he gets it wrong!

Transat Jacques Vabre
This is a duo race mostly for Open60's, Openmultihulls (Orma) and Class40 boats.

Big race, 60 pure racing boats on the way.

Weak winds. Safran is ahead with a 6.8k average. First Class 40 is "Télécom Italia", the little brother of Safran (same designer:Verdier / Van Peteghem / Lauriot ) with an average of 6k. Lots of top class40 ahead of the old Open60's.

Quote:
Originally Posted by Chris Ostlind View Post
Kinda confusing, guys.

There are two types of craft entered... Monos and Trimarans with not one single cat of any kind.

Within those type distinctions, the trimarans are classed as:
Open 60, ORMA designated boats
Class 50 tris

The Monos are classed as:
Open 60 IMOCA class craft
Class 40
Sorry about that. I wanted to say multihulls and I wrote Cats . I am going to edit that on the first post. Thanks .

Quote:
Originally Posted by Pericles View Post
Vega,

Open 50s rather than 60s, The chart is useful as it's possible to select all the boats and see their position relative to each other.

Pericles
Chris is right. The 50ft boat are Open multihulls.

But it is very important to take in consideration that they did not start at the same time.

About the monohulls, the first 40class boat is ahead of about 1/3 of the Open60s (6 behind) and that is awesome taking in consideration the huge difference in size, price and technology (canting-keels and materials).
That's great but only possible on light winds.

Quote:
Originally Posted by Pericles View Post

I would love to have a Gunboat 66, when and if the next Jacques Varbre takes place and shadow the leading ORMA, probably Groupama 2, all the way to Bahia, Brazil and about a few miles from the finishing line, let the Gunboat have its head and surge past the trimaran, to take line honours, whilst having a good meal at the table and glugging the Bolly.

It's an eleven day passage, hardly time to get used to being at sea and the vessel would be on autopilot for 90% of the voyage. The helm is a joystick.

Some may argue that the Gunboat 66 will not have the speed, but a heavier Gunboat 62 has exceeded 36 knots. I'd be delighted to give it a go.

….

Am I dreaming? Absolutely!

Pericles
I hope you don’t mind that I reply here.

Yes you are dreaming. There is an incredible huge difference between a fast cruising cat like Gunboat 66 and a top racing trimaran like Gruparama. It’s like to say that a Ferrari F50 can be a match for a F1. Fact is that a simple racing formula ford, with be faster on a track.

Even an Open60 would be faster than the Gunboat. The Gunboat can make 36k? An Open60 also, even more. What counts is the wind needed to go fast.

If the conditions were very bad, as had happened on other races, you would see that the difference between the trimarans and the Open60’s would be a lot smaller and that the trimarans would experience a lot more retirements from the race than the monohulls (breaking, capsizing).

I like both types of boats, but we have to be fair regarding the strong and week points of each one and to see the diference between top racing boats and fast cruising ones.

Regards

"Even an Open60 would be faster than the Gunboat. The Gunboat can make 36k? An Open60 also, even more. What counts is the wind needed to go fast." Gunboat speeds are posted on their site. Where is your reference for IMOCA speeds and in what wind speeds?

Vega with remarks like that , you should not be so eager to post. Better you hide your lack of knowledge, rather than confirm it to all and sundry. Learn from the man! Guillermo is a NA. See his site. http://www.gestenaval.com/

Hell's teeth, if you bad mouthed my professional competence in the field in which my own company operates and I came face to face with you, I would not be so patient as Guillermo and you would be holding your teeth on your hands. I'm English and settling such contentious disputes after due warnings, is a great tradition with us.

So, let's all shake hands metaphorically, agree to disagree and treat the professionals who share their knowledge here with due respect. If they were to leave, we would be the poorer.

Pericles

Vega

11-12-2007, 06:50 PM

Paulinho,

As always when talking stability, you have no idea of what you're talking about.
.....
Please don't play NA anymore, it's totally ridiculous.

Guillermo, refering to my knowledge on boat stability (yesterday, on other thread):

http://www.boatdesign.net/forums/newreply.php?do=newreply&p=169941

Another new light kid in the block, with an strange categorization.

Sun Odissey 36i is said to be a Category A boat (So STIX >= 32), but with the posted info I cannot get more than a 26,67 figure for STIX, even assuming downflooding angle coincides with AVS (+/- 123º). Minimum AVS for this boat to qualify for A category = 117,6º

Dynamic Stability Factor (FDS) = 0,574 (because of the poor GZ curve)
STIX = 26,667

DESIGN CATEGORY B

How the hell they get a STIX of 32 or higher...? Do the posted GZ curve correspond to MOC? :confused:

It looks to me a nice boat with a good stability curve.

It is obvious that the magazine as messed out with that curve (it is not the first time). I believe Jeanneau provided a correct one.

You should know that boat, with those characteristics (beamy, with a bulb and that ballast) could not have a Max GZ lower than 0.4m.
I believe that it is a RM curve and that where is 0.4 should be 4.

The GZ curve could very well be that one, precisely due to the beam, low ballast/displacement ratio, high freeboard and upwards volumes.

... I am absolutely sure that 0.39 is not the MaxGZ value.

The Max GZ of this kind of boats (jeanneau 36i) lies between 0.6 and 0.8. ....

A Max GZ of 0.39 for the Jeanneau 36i (as it is on that curb you have posted) is inevitably a big nonsense.

I have received the stability curves from Jeanneau. They seem to agree with me that RM curves are more appropriated to judge the boat stability:P , because they only have sent me RM curves:).

It looks that I was right.

The curve posted by you and published by PBO magazine is a RM curve from the GTE version (draft 1.94) with the boat in MaxSail condition.

The curve published by Yachting Monthly and posted by me it is a RM curve with the boat in MinSailing Condition (the MinSailingcondition curve for the two different draft versions is identical).

(By the way: Your last posted curve seems to be also wrongly displaying units at the ordinates axis. Those cannot be mt)

I believe “mt” stands for moment?

If this is the case I don’t understand what you mean. The units are clear, they refer to Kgf*m.

...

Maximum GZ for that asumed load condition is around 0,54m. If the PBO stated figure of 5725 kg is the real MOC, variations are not very great and GZ goes to around 0,58m.

again:

... I am absolutely sure that 0.39 is not the MaxGZ value. The Max GZ of this kind of boats (jeanneau 36i) lies between 0.6 and 0.8. ....

I have received an email from PBO, the magazine that had published that curve:

"You spotted a mistake! We normally publish the GZ (righting arm), but the numbers on the vertical axis of the graph of the Jeanneau were incorrect.

This wasn't inaccurate information from Jeanneau - it was a problem this end, for which I apologise.

The shape of the curve is correct but the maximum righting arm should be approximately 0.66m".

David Harding
Technical Editor - Practical Boat Owner

Paulinho,

As always when talking stability, you have no idea of what you're talking about.
.....
Please don't play NA anymore, it's totally ridiculous.

:rolleyes: :rolleyes: :rolleyes: :rolleyes: :rolleyes: :rolleyes: :rolleyes::rolleyes: :rolleyes: :rolleyes: :rolleyes: