Seaworthiness

Now I am not only “Ignorant” but also dishonest.

What I have posted was a direct answer to sequential posts, I mean without other posts, mine or yours, related with the issue.

The first one was post 9, this one:

I have disagreed (about GZ/RM) in post 18, this one:

You have replied with post 21, this one:

I didn’t like the tone of that answer and have quoted Leif Angermark Marin on the subject, on post 23:

And what you have posted now, was a direct answer to that post, not to post 18, and it was posted on post 27.

You give the impression that what you have posted now:

…….was a reply to my disagreement about the Rightening Arm (instead of rightening moment) being the right way to evaluate or compare boat’s seaworthiness. But it was not. The answer was:

“You must be kidding”.

You never said that we should take into consideration the RM values and the RM curve (instead of the GZ curve) when we make an evaluation of a boat’s stability, so I assume that you still think this way, regarding GZ/RM.:

So I really don’t understand why you say I am dishonest when I say:

Or when I quote your direct answer to my disagreement with you about the importance of GZ versus RM in the evaluation of a boat’s stability..

I believe that everybody knows that you know that the RM values are obtained from GZ values X displacement.

 

I'd appreciate if you could show us the stability curve of both versions (or data from them) along with displacements, to support your statement. I have some doubts about it.

On the other hand, their STIX will most probably not be the same as sail areas are not the same, nor the centers of effort, nor displacement, neither the hull's lateral projected area geometric centre.

I would like to know for sure for what version of the POGO is the STIX calculation you posted in pieces (Why didn't you scan and post the whole thing? )

Analyzing the two pieces you posted, I think it would be very interesting to know what mass values were used for MTL (Ballast water tanks empty? full?) and MOC, as MTL seems to be bigger than 1.15*MOC. The calculation presented is the one corresponding to the MTL condition. Usually the STIX for MTL condition is higher than the one for the MOC, and ISO 12217 rules that the lower figure is the one to be used as the definitive one. The STIX figure uses to be the one for the MOC condition. So maybe (only maybe, but quite probably) the real STIX number is lower than 44.7

Interesting to see FIR (Inversion Recovery Factor) is lower than 1, as well as the FDL (Displacement Length Factor) and the FBD (Beam Displacement Factor), as it was expectable. Two main contributing factors to rise the STIX are the FDS (Dynamic Stability Factor) and FDF (Downflooding Factor). This last goes to the top permited value of 1.25 due to the big beam (most probably giving a high downflooding angle) and the FDS also goes to the top of 1.5 also very probably because of the same big value of the beam influencing the downflooding angle and so the amount of GZ curve area to be considered for the calculation.

Very probably the POGO 40 is strongly supporting the relatively high value of her STIX (If 44.7 results to be the correct one), by means of high downflooding angles (and water ballast?). We have seen the great influence of Dfl figure in STIX calculations (See post 87 at the STIX thread).

I really would like to know her asigned STIX at MOC.

Note: Not important, but the ISO FDIS 12217-2 was a discussion document, no longer valid. The valid one nowadays is ISO 12217-2:2002.

 

I think you are absolutely right. There are a lot of compromises in any sailboat. But I don’t think that a cruising boat should be necessarily wide. I have said:

I don’t think that it was to do directly with ballast, but with the amount of Rightening Moment that a boat can generate at low angles of heel and the relation of that RM with the weight of the boat. I mean, if two boats generate the same amount of RM at say, 12º, but one only weights half of the other, the lighter boat can sail with a lot less heel, because the heavier needs a lot more “Power” to move at the same speed, or even to move at all in troubled seas.

Of course, RM has to do with weight and the length of the rightening arm. Beamier boats with a low bulbed keel can have a much bigger rightening arm and can more than compensate the difference in weight to older boats, regarding the amount of generated RM.

Take a look at posts .411 and 417 .

 

Stupid Pogo....I might put that on my signature......

Pound for pound.

Try comparing the Pogo to a 6T clunky pocket cruiser.
The initial stability of the Pogo is outstanding, but the inversion numbers are awful.


Or the Valiant and a 10T skimming dish. Same again.

Length is a red herring.

Pound for pound gives an honest comparison of two boats.
A boat is a hole in the water, and what designers do with the same displacement is the lowest common denominator.

 

I quoted the first post in this thread to point out that Guillermo is basically correct, in that boats like the Pogo 40 do require a different approach to cruising that more traditional designs.

I don't think there is any real debate about that.

The only debate (for 2 months now) is how demanding the boat might be in extreme conditions.

What speed does it take to keep the keel from stalling? Certainly not very much. The boat sails to weather at speeds from 2 to 7 knots. Thus we know that 2 knots is enough speed to keep the keel working. The boat is stable enough to carry any amount of sail needed to maintain control. 2-7 knots is certainly not "high speed" and reaction time can't be an issue. The boats don't have to be sailed at 20+ knots to be stable, although they are capable of that speed. BTW the Pogo 40 Cruiser does not have a very deep or narrow keel.

I think that one of the problems people have with boats that are not designed to heave to, is that they cannot imagine a boat sailing under control in storm conditions. Traditional techniques were developed for traditional hull forms. Those boats were not designed to sail quickly in storm conditions. They don't handle well under autopilot in heavy conditions, this is no surprise, they were not designed to do so. They are relatively tender and require more sail area to maintain speed, often at large heel angles. Large sail area and large heel angles make the boats hard to steer (by humans or autopilots).

Boats like the Pogo 40, on the other hand, were developed from years of experience designing boats that can sail in conditions that would force traditional hull types to adopt defensive survival techniques. Not only are they designed to sail in conditions that traditional boats find overwhelming, they are designed to do so under autopilot while the crew sleeps. (very seaworthy IMO)

It is not likely that after several generations of design that the boats are less seaworthy. The Pogo 40 does not have an extreme hull form. The beam/length ratio is not outside the range of most other boats of similar size. As Vega has shown, the boat has better numbers than boats whose seaworthiness is not questioned. Indeed the Class 40 rule is a modern rule, the Open rule is outdated by it's static stability requirement (as shown in the R-P study Guillermo cited). The Open rule forces extreme beam and the Class 40 rule does not, it is not valid to compare the moderate Class 40's with the extreme Open 50's and 60's, they are in no way the same.

As soon as one accepts the fact that boats don't have to be as heavy as their wooden ancestors to be strong, one is no longer forced to adopt hull forms and tactics that are proved to work for heavy boats.

Force 9+ is not a common condition along routes that are chosen by cruisers. Yet experience has shown that the Class 40's handle Force 9 while still racing. I don't know that they have been tested in Force 10+. The polars show that a Pogo 40 has the speed to cover enough ocean choose her weather. This is should be no surprise, the boats are designed to race where weather routing is a major factor in success. Since they are racers, the Class 40's must be designed to handle whatever weather that exists when the starting gun fires. They do not have the luxury of staying in port to wait for better conditions (as a cruiser does).

If you look at the differences between the Pogo 40 Race and Cruise versions, you will find that the cruise version is quite moderate. The long, high A:R fin keel is replaced with a shorter fin with a much wider chord. The cruise version's keel should be more stall resistant than the race version. The sail plan is also more moderate. Stability is maintained with a larger bulb and an increase in displacement (5300 kg vs 4800 kg).

I was very surprised to see how weatherly the boat is. In 25 knots true wind, the cruising Pogo sails 35.5 deg off the true wind. Boat speed is 7.43 knots and the VMG is a whopping 6.38. In 30 and 35 knots the VMG is 6.44. This means the Pogo 40 cruiser can sail upwind at greater speed than a traditional design can motor. I doubt that a Valiant 40 could motor dead upwind at 6.4 knots in 30-35 knots of breeze. Of course the racing version improves on those numbers, but we are discussing cruising boats here. What this means to me is that a Pogo 40 cruiser could sail upwind in a near gale against the current at the Golden Gate Bridge. Having attempted that feat in lesser machines, I find that level of performance almost astounding.

Since I can only draw from my experience, I know I find the motion of heavy displacement boats downwind in a breeze less than comfortable. I also know that a boat that is planing or semi-planing has a motion that feels much more stable under the same conditions. I find steering the slow boat much more demanding than steering the fast boat. Downwind at 12-15 knots boat speed in 20-25 true should be much less dramatic than downwind at 8.5-9 knots. At 10 knots the Pogo is throttled back, sailing on the AP, and you should be able to enjoy the ride. It is no wonder to me that hulls that are designed to be stable at high S/L ratios become hard mouthed and cranky when pressed. The yaw > broach > recover > repeat cycle would make me consider heaving-to too. Been there, done that, didn't like it much.

As far as the cruising load goes, traditional cruisers that buy boats based on the "heavier is better" logic, also load their boats with all sorts of crap they don't need. They extend the heavier is better theme to every choice they make. The Valiant 40 will have a 125 pound life-raft mounted on a cradle on deck, the Pogo 40 will have a 35 pound life-raft in a valise. If you look at the requirements for equipment and stores for a 30 day passage, vs what people think they need it is no small wonder that they sail in grossly overloaded boats. They strap cans of fuel on deck, they hang dinghies on davits off the stern, they carry 3-400 feet of chain for the anchor, they carry 3-4 anchors ... People like me that can tour on a motorcycle have no problem traveling light, people that must have a motor home just to get away for a weekend should probably not consider a Pogo 40.

After 2 moths and 400+ posts we are no closer to an objective definition of "Seaworthy" that we can agree on. I hope that those that were certain that the Pogo 40 would have numbers and stability curve that would show how "unsafe" she is have been shown the light.

I think Mike has planted the seed for a new debate:

"bulwarks of the vessel and the secure cockpit protecting you from the sea and the spray and keeping your person aboard and comfortable. These are Seakeeping issues rather than stability but they are part of the seaworthiness of a vessel too.

That wide open shallow stern cockpit will be a wet and insecure place at times. The low deckhouse is scant protection. "

The bulwarks and secure cockpit that hold tons of water, raise the CG and make the static stability lethal?

The high deckhouse, that along with the bulwarks increase the windage of the hull? The increased windage that prevents the boat from being able to make to weather, so the crew can be secure in the cockpit while the boat is driven onto the lee shore?

As long as we are posting opinions, this is just exercise in word play and debate tactics.

Shall we start a new thread? Seaworthiness, Bulwark and Deckhouse height?

Have a great weekend all!

Randy

 

We've been there. Guillermo doesn't think that comparing boats of equal displacement is valid. He also does not like comparing boats of equal cost. (Both comparisons favour light boats).

However, I did point out that the Pogo 40 has about the same displacement as my Catalina 30 ... it would be hard to argue that for a cruising couple the Pogo would be less able to make safe passages. When you study boats with equal displacement, you will find that long light boats are at least as seaworthy as short heavy ones. It you are ready to argue that a shorter boat of the same displacement is more seaworthy than a Sundeer 65 or Deerfoot, you are a braver man than I!

Randy

 

Stupid Pogo.....

Thanks for the new disp for the Pogo RHough. From 6T to 5.3T makes a difference in the calc

Righting Moment (Kgfm) at 12º heel: --- Valiant40 – 2513 --- Pogo40 – 2650

Righting Moment (Kgfm) at 90º: -- Valiant40 - 5027 --- Pogo40 – 4399

Max Righting Moment (Kgfm): --- Valiant40 – edit2:7536 --- Pogo40 – 6360

Max Inversion Moment (Kgfm): --- Valiant40 – edit1:3770 --- Pogo40 – 2915
(still feel funny about the max inversion numbers...find it hard to believe that the Pogo has neg righting arm of 55cm...)
edit1: In fact looking at this graph Valiant looks like 1.2', which would make max inv mom 3770 Kgfm.
edit2: Max righting arm can be bumped up to 2.4' as well
edit3:Gee, the more I look at the graph the more I see. Righting arm at 12deg can go to 0.8', and at 90deg it can go to 1.6' too.And the Pogo gets a few changes as well looking at this other graph.

Maybe comparing a clunky old Valiant 40 to the Pogo isnt instructive.
I remember seeing a post regarding the numbers for a Catalina 30 some where, and I would like to run them against the Pogo. Any clues about the thread or the data would be nice...

Comparing pound for pound shows a stark contrast between boats of thirty years ago and now.
Performance comes at a cost, and pound for pound clearly shows the money cost of performance, and the design trade offs.

 

Here are the C30 numbers I have:

Righting Arm
25deg = 1.178 arm
60deg = 1.777 arm
90deg = 1.168 arm
120deg = -0.105arm
150deg = -1.104 arm
165deg = -1.043 arm

Displacement used for calculation = 12828# (includes 1225 crew weight)

AVS = 118
+ area = 135 deg/feet
- area = 47 deg/feet

+/- Ratio 2.892


VCG above WL = 0.06 (0.37 crewed)
VCB above WL = -0.81 (-0.70 crewed) -1.50 @ 25 deg
Effective beam: 9.545
Beam/Draft Ratio: 4.225
Keel Draft: 5.522
Pounds per inch immersion: 834
Moment to change trim 1 inch: 944

While you are pondering numbers, you might want to include the relationship between RM and ability to carry sail. In loose terms the ratio of sail carrying power to displacement gives an idea of the boat's power to weight ratio.

A boat with Righting Arm = 1 @ 30deg compared to a boat with Righting Arm = .5 @ 30 deg.

Assume Drive to be 10% of heel.

Heel is directly related to RM.

Assume driving force required is 5% of displacement.

10,000# displacement requires 500# drive.
500# drive requires 5000#/ft RM

The RA = 1 @30 deg boat has 10,000#/ft RM available so will only heel to RA = .5 or 15 deg if the curve is a 1:1 slope.

The RA = .5 @ 30 deg boat has 5,000#/ft RM avail able so will heel to 30 deg.

Now increase the required drive to 750#

The RA = 1 @ 30 deg boat can still sail, the RA = .5 boat must heave to, she cannot generate the drive required within her stability limit. She has no choice but to stop sailing. Note that I'm only looking at the force required in general terms. The point is that low values of RA mean that tender boats cannot carry very much sail. At some wind strength, they won't be able to carry enough sail to drive the boat. The stiffer boat can continue to sail in conditions that stop the tender boat.

For equal displacement, the higher RM (longer Arm) should be able to sail in higher wind strengths. For equal RM, the lighter boat does not require as much power, so should be able to sail in higher wind strengths.

Is there a flaw in that logic?

 

5.3T is the lightship weight. The stability curves for ISO 12217 considered the boat in Minimum sailing condition, so you should not consider the light weight to find the RM values. Now they consider not only the MinSC curve but also the curve with the boat in Maximum sailing condition.

The one I have posted is the curve in MinSC, the only one that you can compare with the one from the Valiant, that is also a curve in MinSC.

By the way, the Pogo can carry a huge amount of load, for a boat of this kind (light boat). The boat in MaxLC has a displacement of 7.5T and that is a loading capacity of 2.2 T, more than 40% of its own weight.

 

Ok, now I agree with you when you say "Its a young mans boat", if we consider that youth is a state of mind

The marketing person who has said :"easy cruising miles enjoying a cool beer" , is not a “marketing person” but a boat designer and that quote was not about the Pogo, but about a similar boat, the cruiser-racer 40class boat designed by Owen and Clarke.

The statement is from the boat’s Architects and the full quote is:

"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".

You say about the person that has made the statement that you" have a sneaking suspicion that person has not sailed an ocean before ".

Well, you are very wrong. Merfyn Owen and Allen Clarke are very experienced sailors.

Merfyn was a sailor before becoming a designer, he is a ‘double’ Cape Horner and former round the world race boat skipper himself on the 96/97 BT Global Challenge. He has said about his sailing experience in a recent interview:

" I’m your typical short handed all rounder, but I don’t get enough practice anymore to play at the top end. … I travel too much".

Allan Clarke is “a boat owner and keen cruising sailor for many years, with a number of transatlantic crossings behind him, he has also competed in a number of significant races including the AZAB.”
http://www.owenclarkedesign.com/default.asp?m=da&id=18255


So, I believe they know what they are talking about.

Experience has shown that these boats can be sailed in extreme conditions while racing on autopilot.

In the last “Route du Rhum” the twenty five 40class boats passed through several storms, with winds of 70k. They raced in those conditions and most of the time on autopilot. All of them were 4 to 8 hours a day on non supervised autopilot, while the pilots slept inside.

On those days with winds from 50 to 70k, most of the boats were doing around 18k, on autopilot, without problems.

If the unsupervised autopilots can control the boat at that (racing) speed, they will be super reliable at a more reasonable “cruising” speed, even on extreme conditions.

 

If that is the case interior storage compartment layout is crucial. If the majority of stowage isn't at or below the waterline at least for the heaveist 2/3 of supplies, there will be a negative impact on stability. (I asume that the 2.2T would include all tanks filled) Also, does that include water ballast?

 

I don't believe water ballast is included. That displacement is the one they use to calculate the stability curve in MaxSC.

I believe you are right about the careful distribution of weight, not necessarily below waterline, but certainly not in a high position.

Actually the stability is increased, but also the negative stability.

The Rm at 90º of heel goes from 5100 to 6132 .

 

Paulo
I stand corrected . But I still think, this is a strong marketing line that could deceive many people.

Given the very good curve you posted (I am surprised that they did not give me this when I requested ) It shows a healthier picture (if it is correct for the cruiser) . I would still dearly like the W & M sheet to see just where everything has been put for this and just what cruising items have been accounted for. What happens to the Cp and SAD ratios when the vessel is fully laden I wonder? This is often a problem with performance oriented light boats.

As for a young persons boat it is a performance , not comfort oriented design, Other factors (that we have discussed) still are concerns to its suitability and safety.

 

"this " as in your post or mine If mine perhaps you would like to explain why that is the case.

I was teling Paulo what I meant by abysmal security, but We don't need a new thread this is seaworthiness too.

Do you really think this would be a dry boat going to windward ? My own experience and video footage of this type show that they can be very wet for windward work particulalry so in heavier weather .

Perhaps a bad choice Bulwarks not as is the raised deck edge above the gunwale but as in security, defence against injury annoyance etc.
There is a problem with shelter with low sided, low deckhouse, and open cockpit boats and shelter is important in reducing fatigue.
Would you go offshore in a family cruiser without an effective dodger of some sort? If you do acknowledge the need for some shelter then how do you shelter that cockpit on the Pogo 40?

Heaving-to is a valuable technique I think you are woefully wrong in your contrary opinion. If you cannot heave to you must carry and be able to reliably deploy a drogue as multi's do and that has more attendant problems than a vessel that can comfortably and safely reduce drift or gently fore-reach . You may not properly appreciate this quality in a boat unless you experienced it. Books and articles on seamanship often extoll its virtues.

Numerous cruising loads increment unexpectedly (particulalry when cruising with a family) . Many of these loads , Davits, Radars, Outboards, Dingies deck boxes, furlers, ground tackle, fridge/freezer spares. Computer TV inverter solar cells wind generator, watermaker..... make a cruising boat just that...practical and suitable for the task. Thats why I cannot see the Pogo40 ever being very appealing as a long term blue water cruiser. Either it's overloaded or it's spartan. Comfort and convenince will nearly always triumph over performance.

 

This is putting two boats roughly pound for pound.
Rocket science can go out the window. Your eyes can see the difference in these two boats.

Righting Arm Meters
__________Catalina_____Pogo
25deg_____0.36m_______0.87m
60deg_____0.55m_______1.15m
90deg_____0.36m_______0.86m
120deg___-0.03m_______0.17m
150deg___-0.34m______-0.30m
165deg___-0.32m______-0.52m

Displacement Kg(thank you Vega. Data for 7.5T disp would be interesting...)
___________5830________6000

Righting moment Kgfm
__________Catalina_______Pogo
25deg_______2099________5220
60deg_______3207________6900
90deg_______2099________5160
120deg______-175________1020
150deg_____-1982_______-1800
165deg_____-1866_______-3120

The force required to knock down the Catalina is about the same to re-right the Pogo.
Modern boats are delivering outstanding performance and 'comfort', but it has been at the expense of seaworthiness.

Everyone seems to know how to make the Catalina go faster....any ideas on hull form modification to reduce inversion moment for the Pogo?
If the Catalina and the Pogo had similar inversion moments, I might say yacht design has advanced significantly.
However it hasnt.

Robbing Peter to pay Paul.