Seaworthiness

[RHough]

I seem to be getting dragged into this thread. Arghh!

I agree. The thread is hard to leave.

 

[Vega]

Quoting vega:
"For example, the water ballast, in what refers increased inertia and longer roll periods...."

This kind of mental confusion is precisely the one we should avoid not to go into stupidly circular discussions anymore.

You are a very nice Guy. You are quoting me, but I am not the only one that have said the same. For instance:

.... Guillermo, I think it's a point here about deep bulbs, and maybe water tanks in bilges too, both features will increase the inertia and make for longer roll periods. It is an old rule of thumb, concentrate your ballast lengthwise but distribute it sideways.

It looks like there are a lot of people suffering from " mental confusion" around here.

I did not grossly miscalculated RM1200 STIX. The 32,9 figure was calculated as STIX(100) and not as her final figure STIX, and thas was clearly stated in my post. The more accurate figure of 33,521 is not that far away from 32,9 for STIX (100). What was grossly wrong was "Increasing Dfl to 116º (=AVS) only brings STIX up to 33,531", but you didn't even noticed.
.

Yes, I have noticed that 32.9 is close to 33.5. It is you that seem not to notice that 33,5 is very far away from the real boat STIXs , I mean 38.33 and 38.70.

I do not trust the data you post about these kind of matters, as you have demonstrated to me you either fallaciously manipulate such data or, on the other hand, you post it in good faith but not understanding it.


You said 44.7 is her official STIX, and you still do not know if that is true.

You are incredible. What I have said was:

About the POGO40 STIX, I will post the relevant part of the official document that certifies the boat. No need to make any calculations. They have already been made correctly and ISO certified.

What I have posted is part of the official document for the boat certification and the STIX I have posted is the certified STIX for MaxLoadCondition.
Now they demand the boat data in two conditions: Max sailing conditions and minimum sailing conditions. Stability curves and STIXs for both conditions.

The paper I have posted clearly states (hand writing on top) that it is a Max Load Condition STIX . It says also that it is the page two and that the STIX on Min Load condition is on page 1. I don’t have the page one (STIX on MinSailCond).

http://www.boatdesign.net/forums/attachment.php?attachmentid=11175&d=1169076993

Both Stixs are important because you normally don’t cruiser neither with the boat in MinSailCond nor in MaxLoad Condition. Both Stixs are official certified ISO STIXs.


The reason why you say this, is a mystery to me :

“You said 44.7 is her official STIX, and you still do not know if that is true”.

.

I recommend you yo write the designer and ask him to confirm you in written the thing, before asuming what you have been given is the correct figure.

Yes, everybody is trying to cheat on you, me, the Pogo manufacturer, the certification bodies....and probably also the designer, since, as you know, it is the designer (Finot) that provides the data for the certification process .

 

[Guillermo]

You are a very nice Guy. You are quoting me, but I am not the only one that have said the same. For instance...

Oh...! It was you...!
Are you so confused that you still do not realize why I quoted those specific words of you?

!! Don't bring good old Raggi into our discussion. What you have said is a "contradictio in terminis", and Raggi's is not. Think again....

The reason why you say this, is a mystery to me ...

Yes, I realize STIX is a mystery to you.
Let me explain it to you: A boat's official STIX is a single figure, the lower between the ones for MOC and MTL conditions. The STIX at MTL is only mandatorily calculated if MTL is bigger than 1.15*MOC (read carefully your own paper). After performing both calculations the lower value has to be chosen.

I just would like to know if you are absolutely sure the value you were given is the lower one. Are you?

 

[Guillermo]

...I'm having fun ... I wonder what they will come up with next?

Don't be so happy....! I have been busy with Vega , but I've found several weaknesses and inacuracies in your (very long!) posts, that I would like to comment. I'll come on that tomorrow.
Cheers.

 

[Guillermo]

Let me dare to play around with the still scarce data we have from POGO, the kind of playing a caring friend of mine here (he called me nice guy! ) likes the most...
Let's see:

POGO's BASIC DATA

Lh = 12,18 m
Lwl = 12,03 m
Bmax = 4,40 m
Bwl = 3,52 m (best estimative)
Draught T = 2,20 m
Body draught Tc = 0,50 m (best estimative)
HCE = 6,12 m (rough estimative)
HCLR = -0,88 m (rough estimative)
Disp = 5300 kg (Asumed as MOC)
Ballast, fix = 1800 kg
Ballast, water = 750 kg
Sail area = 90 m2

Approximate (rough) data from posted stability curve:
Angle of vanishing stability = 127 deg
Downflooding angle = 110º - 120º (I strongly think it is not higher than that)
GZ at downflooding angle = 0,4 m
GZ at 90 degrees = 0,86 m
Area to flooding (Agz) = 95 - 98,25 m.deg
Area to AVS = 99 m.deg

With those we get:

Length/Beam Ratio L/B = 2,74
Ballast/Disp Ratio W/Disp = 0,34 (only fixed)
Displacement/Length Ratio D/L = 84,91
Sail Area/Disp. Ratio SA/D = 30,09
Velocity Ratio VR = 1,33
Capsize Safety Factor CSF = 2,55
Motion Comfort Ratio MCR = 12,92
Roll Period T = 1,66 Sec (ideal around 4,5)
Roll Acceleration Acc = 0,44 G's (Ideal around 0.06)
Stability Index SI = 0,38 (Ideal around 1,1)

STIX (Aaaahhhhh, Paaauloooo.....!) (Trembling voice and cadaveric aspect)

Base Length Factor (LBS) = 12,080
Displacement Length Factor (FDL) = 0,891
Beam Displacement Factor (FBD) = 0,744
Knockdown Recovery Factor (FKR) = 1,075
Inversion Recovery Factor (FIR) = 1,044
Dynamic Stability Factor (FDS) = 1,500
Wind Moment Factor (FWM) = 1,000
Downflooding Factor (FDF) = 1,222 - 1,25
Delta = 0

STIX (100º downflooding angle) = 39,90
STIX (120º downflooding angle) = 40,355

So, may we say her STIX at MOC is around 40...? Shall we dare...? (Aaaahhhhh, Paaauloooo.....!)
It's a pretty good figure, much better of what I suspected initially (Aaaahhhhh, Paaauloooo.....!) although not that high (Let's remember, as an example, Eliasson thinks this should be the minimum value for Category A boats)

To make things short, what the hell, here you have it Randy, loud and clear: I don't like the **** boat at all, as a go anywhere cruiser! (Even if her STIX is 60!)

(But you can buy it, absolutely, if you are so in love with her, and we'll talk again in five years time)

Cheers

 

[CT 249]

Chris
I have a very high opinion of the 2nd version of the Top Hat. It should be mentioned here that the boat was designed as a Bass Strait denizon. She is a seaworthy and capable vessel.

Does a baby make a family? I guess it does , Generally the kids are a bit older and mum and dad want some connubial privacy.

Cheers

The design was originally a UK one for racing, according to my contemporary reports. She is of the same general style as Outlaw and other I & P racing machines (light and radical in their day with a steep rule-inspired run) and the original Aussie boats (1st version?) had only a small coachroof and dominated Port Phillip racing in their class. I think that they were always too small for the Bass Strait races.

It's a bit like the S&S 34; in one era it is seen as an unseakindly lightweight rule-distorted racing machine, later it becomes seen as the epitome of a true seaboat by some people.

I agree about the need for mum and dad's privacy. I don't know of many boats at all (including big cats) that have enough privacy for a couple. And yet people are happy with it. It's just another example of the fact that we all have different standards and accept different trade-offs. as far as I can see.


"If the vessel is too light in the ends or has too low a fore-n-aft inertia it will be slower and less comfortable. Shifting mass in and out of the ends even ballast is not uncommon."

I most definitely agree that extremely light ends can create a terrible motion at times. I can find very little evidence that extremely light ends make a boat slower in anything but the rarest of conditions, and then it's easy to move crew weight around (in a racing situation). I do not think you'll find many decent racing boats with ballast in the ends these days; it was always recognised as something to do only to correct trim or rating problems.

Some of the light IOR centreboarders had superb motions because they had so little weight in the ends (of the boat, rig and keel) that the bow and stern would just hang as if suspended. Those of us on the heavy boats racing them would "chop wood" in the same conditions. However, this is in the unusually chaotic sloppy chop and swell off Sydney.

 

[Vega]

Yes, I realize STIX is a mystery to you.
Let me explain it to you: A boat official STIX is only one figure, the lower between the ones at MOC and MTL conditions. The STIX at MTL is only mandatorily calculated if MTL is bigger than 1.15*MOC (read carefully your own paper). After performing both calculations the lower value has to be chosen.

What I have posted is part of the official document for the boat certification and the STIX I have posted is the certified STIX for MaxLoadCondition.
Now they demand the boat data in two conditions: Max sailing conditions and minimum sailing conditions. Stability curves and STIXs for both conditions.

Hum, I thought that you would understand that I was talking about cruising boats, not dinghies. But I suspect that you did not know that all cruising boats have a MTL/MOC bigger than 1.15 (or using the English terminology Weight FL/weight/MC).



Guess what a First 44.7, an Etap 21, a Cyclades 43, a Beneteau 57 and an Hanse 312 have in common. You have guessed, a WFL/WMC bigger than 1.15 (and these are light boats).



And it looks that your French also needs to improve. What is said on that paper is:

“La nouvelle version de la norme demande d’analyser aussi le bateau en charge se mMTL/mMOC>1.15.”
This means :

If WFL/WMC >1.15, the norm new version demands that an analysis of the boat in WFL should also be made.

This is a fully stability analysis, exactly the same as the one made for the boat in WMC, not only the STIX but all the other parameters.

All the recent data that I have seen about cruising boats came with two stability curves and two STIXs, one for the WFL condition and other for the WMC condition. And as I have said:” Both Stixs are important because you normally don’t cruiser neither with the boat in MinSailCond nor in MaxLoad Condition. Both Stixs are official certified ISO STIXs”.

Of course, I find more useful the stability curve, for both situations than the STIX, but this is a welcomed alteration to the STIX norm. (who came you have not posted about it on your STIX thread? )

 

[Vega]

Let me dare to play around ...

STIX (100º downflooding angle) = 39,90
STIX (120º downflooding angle) = 40,355

So, may we say her STIX at MOC is around 40.. (Let's remember, as an example, Eliasson thinks this should be the minimum value for Category A boats)

Cheers

You should not play around with this.

You are way out and that's a dangerous game.

If you want to know the STIX at MinSailCond, ask for the certified data to the designer or the manufacturer.

You have no right to post inaccurate data and made comments based on that data.

Andrew Bray, the editor of “Yachting World” made some comments about the Pogo on the "Editor Column" in one of the last editions:

"Technical editor, Mattew Sheahan sail …the Pogo 40. You’d think that a man who has tested 300 or more boats might have seen it all and be unmoved by the launch of yet another 40ft. But the average 40ft doesn’t leave him shouting:

I want one:p

 

[MikeJohns]

........I most definitely agree that extremely light ends can create a terrible motion at times. I can find very little evidence that extremely light ends make a boat slower in anything but the rarest of conditions....................Those of us on the heavy boats racing them would "chop wood" in the same conditions. However, this is in the unusually chaotic sloppy chop and swell off Sydney.

Even the Dashews have reported the benefits of water ballast tanks fwd in their speedy cruisers.

Off the top of my head regarding studies, have you seen the Stevens Institute 12 meter studies on this? As the pitch Inertia increased the spectra response was studied.
Looking up a synopsis.... Resistance caused by wavelengths of between 6 and 15 metres decreased, from 15 to 25m the resistance was higher. The conclusion is that Cutting through a wave can be better than pitching over it and the forward energy absorbed depends on the resulting flow field against the energy loss of pitching effects.

These changes are significant enough for a racing boat to take this seriously, and significant enough for people not to generalize about it being detrimental.

As for Sydney
I have been more sea-sick sailing out of Sydney on small vessels than any other port in the world! Something to do with two predominant swell directions and those cliffs. I’ve only had light breezes on every departure I've made there. Sailing out of small Southern Pacific islands ( like the southern Cooks) the sea is incredibly boisterous with a large underlying swell (and you are in deep ocean blue water conditions 10 minutes after clearing the reef) but you have over 20 knots of wind constant, the difference is significantly more comfortable. Even there, whether you want the weight in the ends depends on your course relative to the sea, and the length of the boat.

Usually you cannot be bothered shifting the weight around particulalry at sea, you just sail a more comfortable course, but the racers are stuck on the fastest route and would benefit more from this alteration of pitch inertia.

I'm not up with the big racing boats but surely they would do this with water if allowed?

 

[Frosty]

How much do you guys cost?

I mean how much do you put on the price of a boat after youve worked out all this and that.

Whats an eye opener to me after following this thread is that none of you seem to agree --about very much really.

Quoting this that and the other, desperately trying to put down the last opinion.
And when the day comes to launch-- you seem to be the ones more surprised and delighted that your figures are --close.

Actually the word design is not really correct is it?, more of a manipulation of some other of the thousands of already built boats, trying not to infringe someones copyrights.


So to repeat myself how much does the 'designer' actually put on to the cost of a boat?

 

[MikeJohns]

I seem to be getting dragged into this thread. Arghh!]
…………………………….
GM is only an indication of initial (small angle) stability. Boats with a high GM will be stiff, those with a low GM will be tender. All the stability criteria I know of specify a minimum value, but none specify a maximum value, although it is certainly possible to have too high a GM for comfort (fast accelerations inducing sea sickness).

PI

Welcome
Like the Eagles line from ‘Hotel California’ ....."you can check in any time you want...."

I am referring to GM as a significant design factor in any vessel. I am trying to get Randy (RHough) to understand that he was confusing issues on an intuitively incorrect basis.

As an Engineer I shudder at the thought of a carefully considered design being rendered unstable by a rigger who advises that the heavy masts be replaced by light spars because of a partial understanding of the issues therein.

I wanted to know if he really understands what happens if you remove a heavy mast and replace it with a light mast on the basis that it will "improve " stability. The easiest way of illustrating this is to consider what happens to GM. Anyone aware of the issues is immediately aware of the ramifications.

A paper type engineering approach fully considering Gyradius, Mass distribution, Heeled waterplane inertia, GZ and wave induced dynamics etc would be thorough, there are studies that could have been referred to but then we are accused of various crimes like dishing up old science not applicable to modern vessels. Posting well written non-technical articles ( Back in post 414 I added a well written non-technical article by Mr John Vigor) doesn’t seem to help either.

I’m usually at work and have scant time to produce thoroughly ‘legal documents’ unfortunately some here are more interested in the art of debating than in the “art” of Marine Engineering ( although debating can be fun, it does prevent discussion). If you write something in a way that can be misconstrued outside of the continuing exchange then that is what occurs and with a vengeance.

I would welcome your involvement too.

 

[PI Design]

Hi Mike,

I can only really join this discussion from a theoretical perspective becasue, whilst my NA degree specialised in yachts and small craft, the type of NA I practise is on altogether different vessels. Also, dare I say it, I have never, ever, sailed on a lead ballasted boat.:!: All my sailing has been done on dinghies and multihulls (beach cats, Prouts and Dragonflys).

But I do feel I can contribute on the technical and theoretical aspects. Personally, I would not use a Pogo 40 as a blue water ocean cruiser but I would consider one for coastal cruising.

I do agree with Randy's opinion that sea worthiness should not be maximised at the expense of fun, or cost. Any boat only needs to be adequately seaworthy, no more. I also agree that seamanship is vital and that the boat can only be expected to do so much if in the hands of a poor skipper. However, there will always be occasions when even a good skipper has a bad day and he should be able to rely on his boat to provide a certain level of survival capability.

There are perfectly good reasons why most blue water cruising boats don't look like POGO's. And it is not because those designers are uneducated or unimaginative...

Perhaps however, with better comms equipment, better survival equipment and other advances in technology the traditional cruising form may adapt to become more similar to today's racer. Certainly the general public, who are ignorant of boat design nuance, will perceive the Open 60 style as more glamorous and up to the job. One would like to think that most live aboard cruisers are a bit more knowledgable than than the general public though!

Cheers.

 

[RHough]

I am referring to GM as a significant design factor in any vessel. I am trying to get Randy (RHough) to understand that he was confusing issues on an intuitively incorrect basis.

No, you are adopting a smug, patronizing attitude that is typical of people with large egos that think they know more that the people that they are addressing.

As an Engineer I shudder at the thought of a carefully considered design being rendered unstable by a rigger who advises that the heavy masts be replaced by light spars because of a partial understanding of the issues therein.

Here you make it clear that you feel superior, you capitalize "Engineer" and do not capitalize "rigger".

I wanted to know if he really understands what happens if you remove a heavy mast and replace it with a light mast on the basis that it will "improve " stability. The easiest way of illustrating this is to consider what happens to GM. Anyone aware of the issues is immediately aware of the ramifications.

Excuse me, a lowly rigger, for having the gall to question what a mighty Engineer has to say.

One one hand we have Mike (the Engineer), who insists that GM and low angle stability is improved with a heavy rig in a "carefully considered design".

On the other we have Skene who states "As stated, the amount of metacentric height is an indication of the stability for very small angles only, and for this reason cannot be used for determining sail-carrying power and is no indication of the range of stability."

We can also list the boats that have Carbon Fibre rigs as options on otherwise identical boats, Swan, J-Boats, C&C, Beneteau to name the first that come to mind.

If you incline a boat to 90 degrees, heavy rigs reduce the RM. Weight aloft reduces stability at large angles.

No "carefully considered design" that I am aware of has a rig that is any heavier that it has to be. I asked an Engineer for an example to no avail.

Skene also states "A large metacentric height represents great stiffness and tendency to return quickly to the upright from small inclinations. This causes a violent motion when among waves and is to be avoided in power-driven craft where the steadying effect of sail is absent."

PI Design echos this with "GM is only an indication of initial (small angle) stability."

From Selene Yachts:
"Metacentric Height (Gm)
Metacentric height is a measure of the vertical distance between a yacht's center of gravity and its "metacenter". In simple terms, the center of gravity is the point along a vertical line drawn through the exact center of the hull where the hull would be perfectly vertically balanced. There is an equal amount of weight above and below the center of gravity. The metacenter is the point along this same vertical line around which the boat will heel for small angles of heel (less than about 5 degrees). This point could be thought of as the "hinge" point around which the boat tilts as it heels at small angles (at larger angles the change in shape of the submerged hull has a more significant effect). The metacenter is always above the center of gravity. Otherwise, the boat will capsize, since it's weight is centered above the "hinge" point.

The distance between these two points is called the Metacentric height, and is a measure of stability (resistance to heeling). A yacht with a large metacentric height will tend to be more "stiff"—it will be more resistant to rolling. However, it will also have a more violent motion and shorter period when it does roll because of the larger force (called "righting moment") that is exerted to right the boat. A smaller metacentric height means lower stability—less resistance to rolling, but a gentler rolling motion as well."


We are faced with what seems to me an impossible situation. Mike (an Engineer) shudders at the thought of a carefully considered design being rendered unstable by a rigger who advises that the heavy masts be replaced by light spars because of a partial understanding of the issues therein.

Since they don't seem to be harmed by replacing heavy alloy rigs with lighter carbon spars, can we assume that Swans and J-boats are not "carefully considered designs"? (perhaps they should consult an Engineer?)

That might come as shocking news to the majority of sailors. But if an Engineer says that it is so, who am I as a lowly rigger to question the wisdom of that Engineer? Particularly one that also states: "I'm not up with the big racing boats ..." and "we are accused of various crimes like dishing up old science not applicable to modern vessels."

Could it possibly be true that studies of steam ships and twelve meter yachts have very little application on vessels that are very dissimilar to those in the study? Upwind the Pogo is sailing at S/L of .95 to S/L 1.2. Off the wind S/L ratios are 2.0+

How many of the boats that Marchaj studied were operating at those speeds? How much of the old science you base your opinions on deal with sailing hulls in that speed range? Is it just possible that you don't know much about sailboats that at high S/L ratios? Is it possible that the designs of Swans et al are indeed carefully thought out and you are wrong?

Any chance of the designers of fast sailing vessels having a better grasp of what works and what does not than you do?

I am not the only one that has noticed that you are unable or unwilling to answer simple questions. You have repeated a version of "intuitively incorrect" in more than one thread, and implied that those that don't take your word "as an Engineer" or come to the same conclusions as confused, uneducated, or un-professional.

Just in case you missed it while trying to change the subject ...

What is an example of a boat that you think is a "carefully considered design"?

What is the weight of the rig? To be clear, I will define the "rig" as the spars, standing and running rigging, and sails.

What percentage of the total weight is the rig?

What percentage of the total rig weight are the spars?

If the spars were replaced with ones that are 30% of the weight of the ones in the "carefully considered design", what effect would it have on VCG and hence GM? What effect would that change in displacement, VCG, and GM have on the AVS? In the units of your choice, describe the difference in motion.

A mast section on a 50 foot boat might have a weight of 5.6 pounds per foot and the spar might be 65 feet long for a spar weight of 364 pounds.

50,000 pound is not an unreasonable weight for a 50 foot boat with a 45 foot waterline. 364 pounds is 0.73% of the total displacement.

Changing the spar from alloy at 364 pounds to carbon fibre at 110 pounds is a 254 pound change in displacement (0.51%).

Just how much is the GM going to change after a 0.51% change in displacement?

Would a drunken rigger notice the difference in motion?

 

[RHough]

To make things short, what the hell, here you have it Randy, loud and clear: I don't like the **** boat at all, as a go anywhere cruiser! (Even if her STIX is 60!)

(But you can buy it, absolutely, if you are so in love with her, and we'll talk again in five years time)

Cheers

I get the hint. Since you don't like the boat, you probably plugged in numbers that will give you a objective reason not to like it. I would probably plug in numbers that would favour the boat, that is just human nature.

As I said before, the Cal 40 faced very similar reactions. That boat proved to the sailing world that the traditional thinkers were wrong the boat is not unseaworthy.

There is no question in my mind that my Catalina is seaworthy. I don't have a death wish and I cannot hold my breath for very long, but I'm going to sail the boat to Hawaii.

Likewise, the Pogo is more seaworthy that the Catalina. I hope no one will argue otherwise.

It is quite obvious that no one in this thread is going to change their minds. I'm tired of the insults to my intelligence and profession.

Thanks for providing an entertaining thread.

Fair winds.

Randy

 

[MikeJohns]

Hi Mike,......... I do feel I can contribute on the technical and theoretical aspects. .......

PI

That would be good.A few people seem to think that we (the Engineer/NA's here) make it up as they go along and that we are colluding in some way. Although I'm not quite sure how Guillermo wants his thread to go from here.

I think too that the Pogo would make a brilliant coastal weekender, great fun. The stability data supplied by Paulo (Vega) appears very good.

We do not endorse the use of STIX in Australia since its wave height of 7m for offshore is considered considerably too low for the Eastern and Southern coasts and Bass straight. The Tasman sea and the Southern ocean are prone to severe gales in all seasons and some troubled sea-states are generated. Tends to make some of us a bit conservative

What we should be able to do is to discuss the compromises that are made for speed with objectivity.

Cheers