Seaworthiness

Beamy boats or not, there are very few boats, even old types, that can right themselves in completely flat water. For that is needed an AVS of 180º and that means, no negative stability.
There are not many, because that is not needed. Modern boats do not capsize (inverse) on flat water. Big waves and heavy seas are needed.

The same sea motion that managed to capsize the boat will right it. For returning the boat to the "normal" position it is needed a much smaller wave. If the boat has an AVS of 150º, the next wave will do it. If the boat has an AVS of 120º, the average time is about a minute.That's why modern cruising sailing boats have an AVS around 120º (the negative area under the RM curve (negative stability) is roughly proportional to the AVS).

Of course, a bigger AVS is better for returning to the “normal” position, but as you have said, if bigger, than the positive area under the RM curve (and the initial stability) will be smaller, and that means not only a slower boat, but a easier to capsize boat.

Some compromise is needed here. If you know what you are buying, than you can chose the type of compromise that suits you better.

 

I was more interested in drawing you out, on the action of a wave to right the boat.
The same wave action that capsized the boat will act to right it also.
It is not a function of 'time'.
It is applied forces.
On the hull.

I am hazarding a guess here but, are you suggesting that reduction of AVS and increase of righting moment is inseparable?

• If you start adding more beam, your AVS shrinks as initial stability increases.
  That is a performance trade off with seaworthiness.
  You may be happy with 120 deg, but be truthful about exactly what you are trading it for.
• Maximising righting moment is increasing the distance between CG and CB or increasing CG/CB values.
  From the point of seaworthiness, increasing beam is inferior to lowering CG or increasing CG/CB values(redundant strength and displacement are a happy union).
  Ballast and the keel have maximum effect halfway through an inversion.
  Halfway through an inversion, beam will start to work against you.(side deck turns into a full length keel, not very slidy)
  Beam diminishes the righting moment after the peak quite rapidly.
  That is why beamy boats have a RM curve that becomes a cliff after max.

A seaworthy soloution would be to keep a high AVS and use a heavier boat with larger righting moment.
Bigger boats stand up to bigger weather.

This image is from the Finot site.credit only, Finot are a bunch of great guys
When I look at it I think of a variety of forces that will act on it in heavy weather.
I can definitely imagine a more seaworthy design.

 

Paulo
My comments are in black

[quote Vega;]
….. it seems clear to me, neither you or Guillermo are oceangoing sailboat designers.

Please be assured that yacht design is perfectly within my capabilities and I am no stranger to its requirements. Plans are available from me and I do design them.

[quote Vega;]
Some of the “ignorants” that have opposed your marginal views on seaworthiness ………...

Inflammatory conduct is childish, as is this sort of reasoning.
The moderate views I have presented are mainstream, not marginal, I would also like to know what views you refer to rather than these blanket statements.

[quote Vega;]
I have nothing against heavy boats…. I have changed my opinion, not on the seaworthiness of those boats, (narrow heavy boats with long keels), but I believe now that it is not the only way to achieve a satisfactory seaworthiness...........

Nor do I, as I have said. You may also be confusing long keel with full keel ?

[quote Vega;]
Those heavy boats, if well designed, are seaworthy, but there are other types of boats, not necessarily heavy that, if well designed are also seaworthy..................

Absolutely, and we were trying to discuss why some boats are seaworthy and some are not. It is frustrating that people like to play on this dualistic idea of one extreme or the other.

[quote Vega;]
I have changed my opinion based on statistic data and on the different ways the best modern NAs solved the problem, and understanding how they got their seaworthiness from their boats................

Yes you made this clear before this is your argument that you believe that the boat must be seaworthy because you believe that the designer would not design an un-seaworthy boat. This argument could be right for some designers and wrong for others.
How can you tell the difference ?
How do you account for the past failures (dangerous boats) that came from such a design office ?

[quote Vega;]
It is obvious to me that all respectable NAs would refuse to Design an Oceangoing cruising boat that they wouldn’t consider seaworthy.

Yet history shows that designs of racing hull-forms with rule driven inherent faults become attractive to the public and these designs are then offered by designers because that was the market demand. Consider the design briefs.

[quote Vega;]
The boat that Jean Marie Finot has designed for his own personal use, an oceangoing sailboat (the Cigale), goes against all notions you have of what a seaworthy boat is, but it is clear that he wouldn’t design an unseaworthy boat for himself. It is evident that he does not agree with your rather restricted view of boat seaworthiness.

That is for him to say of course and he may have a completely different view happily aware and accepting the tradeoffs.

My “restricted view “ may not be as restricted as you seem to think, so far you have not been interested in moving past this refusal to accept any argument against the extreme hull-forms.

[quote Vega;]
The evaluation Groupe Finot makes of the Pogo 40 (one of their designs), strongly contrasts with yours, but of course they know the boat and you don’t,

And they will not even provide a stability curve. (I asked for one) looking at the photo’s on the promotional website the vessel looked surprisingly tender and vulnerable to me for such an extreme beam. I would very much like to see all the data on the boat, then we could be a lot more specific.

If you have never done a Weights and moments calculation on a vessel you probably do not appreciate how quickly the COG can rise on a light boat, particularly a beamy light boat like the Pogo 40 when you start adding a cruising load. I suspect that this is the main reason that much of the specific data is withheld, because it can be used by technical people to show that they are problematic hull-forms.

[quote Vega;]
“Designed for true offshore competitive performance [racing] 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 cruiser, with the foot released a little of the accelerator and a cold beer released from the ice box! “

This is marketing hype, it is applicable to coastal cruising on some days in some areas for sure, but blue water…………

[quote Vega;]
I have to say that I have something against the particular arrogance that you and Guillermo insist, against all evidence, on that choice (narrow, heavy, full keel boats with a S/D inferior to 16) as the only acceptable choice on seaworthiness.

Where do you get this astounding revelation from ?
This is not true of what I have said.
I have tried to discuss variations in design and indicated the effects those variations have on seaworthiness and stability.

From my viewpoint the evidence that you proffer so prolifically is neither available for scrutiny or debate since it is mostly an opinion formed from your own observations or someone else’s opinion recycled.

Also when you say against all evidence don’t you mean against your opinion? You appear to be saying that we have the arrogance to disagree with you.


[quote Vega;]When you call ignorant to all who don’t share your idiosyncratic idea of boat seaworthiness…………………..

I have not called anyone ignorant. This is getting more offensive and inflammatory.

I didn’t invent what you refer to as my idiosyncratic view, I learnt it from many notable people who observed, researched studied, designed and tested over the years, this science is what I apply in my work, I am happy with it I understand it and I keep asking for studies to the contrary. If they existed I’d change my views. I have said this before.

[quote Vega;]
………I feel a lot better to be on the side of the Ignorant, like Farr, Finot and the others. ……….. Look at the difference in qualifications, to produce a relevant opinion on sailboat design and seaworthiness, I mean, between you and them.

This is another nebulous emotional appeal however you are using the word ignorant again. I have never called these people ignorant, they are brilliant yacht designers far in excess of my skills and abilities to produce performance yachts.

Understand that a Naval Architect can be unqualified in many places (including some US states states) but an Engineer cannot . Bruce Farr for example describes himself as a Naval Architect but he could not register as an Engineer since he lacks the degree. This doesn’t make him any less brilliant, he is not as well qualified academically, but I would suggest that he is a better qualified person to design a racing boat (from his experience) he may not be the best person to design a cruising boat because of his own personal bias towards performance.

[quote Vega;]
I also find that putting all Seaworthiness emphasis on Capsizing and recovering from capsizing, forgetting all other factors, is not the right way to look at the subject.
The better or worst ability to recover from a capsize is an important factor, but by no means inferior to the better or worst ability to RESIST to a capsize.

It’s inconvenient isn’t it but it is called stability and it has a very great bearing on boat design, the safety of the vessel and the people therein. I’ll come back to this resistance to capsize later.


Paulo
I would like one scientific study, paper or prelim discussion that supports your view that the extreme cruising hull-forms don’t compromise seaworthiness. Not your opinion.

Since you put great store in popular views as I said before I can quote to you the names of many prominent people Engineers, designers, riggers magazine editors technical writers etc who do not agree with you, and see significant problems with the extreme cruising and racing hull-forms.

Consider if you tried using these sorts of argument to convince the authorities to change the rules for unrestricted commercial operations (offshore). The working groups consist of or are guided by groups of qualified as you call “idiosyncratic” professionals who would find your reasoning less than compelling.

Rather than dishing up endless biased general observations, how about some specifics ? I can see many fallacies in some of your arguments If this is to proceed you need to behave more professionally (less emotionally).

 

Rather than dishing up endless evasion when asked specific questions, why don't you provide the data that you claim to have?

Define "stability" so we may unemotionally evaluate it.
Define "extreme" so we will recognize it when we see it.
Define "seaworthy" so we may discuss it.

As a degreed engineer, you should have no trouble defining those terms objectively.

Once we have an objective definition, we will know what you are talking about. Until that time you will have to put up with childish, unprofessional, emotional responses.

I tried to get some specific responses by posting objective criteria and got none.

I have asked specifically for clarification of what is meant by "heavy" "light" or "extreme". No one seems to know what you are talking about.

Are you here for debate or discussion?

The engineer's I know have no problem answering specific questions within their realm of expertise. Why is it so hard for you?

For you to insinuate that designers and manufactures have sold dangerous boats because they are the fashion is to question their ethics. Was that your intent? Or is it more likely that *you* think they are dangerous but their history of safe operation does not support your opinion?

I know for a fact that a vehicle with zero stability can be safe. Obviously safety and stability must mean different things to us. Why not provide the definitions so we can discuss them?

As far as I'm concerned, Paulo's post pretty much sums up what I have thought about your statements. I am not the only one that finds your posts patronizing and condescending. If both of us got the same impression, what does that say about your ability to make yourself understood? If your goal is intelligent, professional (unemotional) discussion, I suggest you re-read your posts and see how we could possibly have misunderstood you so completely.

Randy

 

I am going to have a go at this...

• Initial stability.
  Performance mainly.
  Hull form.
• Righting moment.
  Safety.
  Righting moment curves should demonstrate nice things at large angles of heel.

• Angle of heel where maximum righting arm occurs.
  Increasing beam reduces this angle.
• Keel scantlings.
  The longer you need to study these, the more likely it is to fail.
• Spade rudders.
  Sorry but a partial skeg at least,is the minimum.
• Hull form.
  If it looks like a pointy raft with a keel stuck on, that is exactly what it is.

That the boat remains afloat, regardless of conditions(!).
When the worst is over you can propel the remains of your boat to land unassisted(self rescue, scary but responsible).

• the hull and integral keel remaining intact(I hope we are united on this)
• bouyancy being solid(currently optional, bit hard to push right now)
• self righting
• with a functioning rudder(neglected wee thing)

I would like to ask if you guys in the thread would answer RHough's questions as I have.
He has cut to the chase with some simple questions, and it would be revealing to see each others view points lined up...not who has the biggest one, but what it looks like.(!)

Or you can shred my post

 

At last, someone mentions skeg! Rayk, couldn't agree more but haven't dared to write, will we get flamed now?

The extreme section should include keel area vs. sail area and rudder area vs. sail area.
Some cruiser / racers have KA/SA in the lower 3% range, this is too low to belong on a yacht advertised as suitable for ocean cruising. What's the lower limit? Personal opinion: just below 4%. This is also linked to roll-damping. Adequate roll-damping is an under-rated issue and is an important part of seaworthiness.

Now you can thrash my post

Mikey

 

No.

This is why the full thread is raging.

There are reports of 100 ft breaking waves. Check for rogue or freak waves. These waves damaged or even sank big ships. And they are more probable than once though.

I do not think any leisure yacht (under 80 ft), could survive to such waves, unless it is completely unsuitable to leisure boating.

On another hand, ISO category A for over force 8 winds and 4 m waves also says safety up to force 10 winds and 8 m waves is checked. I do not have the exact phrasing at hand, but I think it states that abnormal conditions such as hurricane or typhoon are not considered (.. or so).

So this thread is not a technical one, just an emotional one about up to where a leisure boat have to survive.

 

Fair enough fcfc.

How about answering RHough's three questions though?

 

Hello Rayk Randy,[RHough] FC and Mikey good to see you made it through the festive season..

Randy
I may have missed some of your comments or skipped your posts before because I found them deliberately provocative, or I may have been deep in the celebration of the season and forgotten, please be assured it was not intended to deny you the one true insight
I do have trouble identifying whether you want to really discuss the issues or whether you just want a rollicking debate sometimes, looking back I see I did miss one quite sensible (even professional) post. I also noted you were talking with Guillermo so figured he was answering your queries.

At one extreme is the narrow heavy deep hull with a D/L of 400 and a massive wetted surface area and a small rig and a LPS of close to 180 degrees at the other extreme is a wide beam wedge shaped light weight with a D/L of 100 and an LPS of 110 degrees.

In between we have the more practical cruising hull-forms which may tend one way or the other or sit nicely in the middle ground (water).

We defined seaworthy pretty well early on in this thread, I’ll stick to the one I posted.

As for stability we separate that into static and dynamic the dynamic stability is more important, the static is a guide but not an absolute in a seaway. To fully understand this needs more than a few lines in a forum but it is the interaction of water and hull and the transfer of energy.

Hopefully you are reading “Seaworthiness” avidly by now (if you really are interested in this thread). This will enlighten you more than you can imagine . You are reading it aren’t you?

OK now we can all be mature considerate and reasonable posters and get on with some technical discussion?

They make mistakes and they rationalize like most people, so I’m not insinuating it I’m saying that they have designed unseaworthy boats.

For an example we could talk about hull-forms that foundered, or we could go for a simpler example and consider a design fault (other than hull-form) like a technical blunder;

Lets consider one mistake , a vessel designed by Farr since he is the flavor of the moment. The Coroners report (since there were deaths) found that the vessel was designed to incorrect scantlings which led to the keel separating from the hull. No engineering analysis was done and the scantlings (the magic numbers) were deficient so the keel fell off after a critical number of stress cycles. Farr was not unethical but the class of boats were dangerous and un-seaworthy without extensive modification. Hence my comment to Paulo [Vega] how do you tell an un-seaworthy boat from a seaworthy one if you believe all boats from that designer will be seaworthy.


Hows that, are you happy with this ?

 

Mikey
I will not design a rudder without a skeg, I try and talk the skegless people into a strong half skeg and a sacrifical bottom to the rudder. So many boats have foundered because of rudder failure. I see a lot of rudder damage and associated hull damage from long deep unskegged rudders hitting things.

I tend to agree with you on the roll damping and lateral areas. Chines add some significant roll damping too if they have enough of an angle.

We commonly design anti roll keels for round bilge fishing boats, something that could have been designed into the underwater hullshape without the added surface area of the anti-roll keels.

Sorry this is brief got to go.

 

For all the heated language, I think you guys actually agree on most things. A heavy, narrow boat has a certain 'self righting' ability and motion in a seaway that many consider to be the essence of seaworthiness. Wider, lighter hulls have a different response - often with higher initial stability but a lower AVS and shorter roll period. Those facts are not open to debate, they are the result of the physics that influence them. Where you seem to disagree is whether seaworthiness can only be achieved by a high AVS, small negative area and long roll period.

One view would be that any boat that has racked up, say, 30,000miles in a variety of conditions must, by definition, be seaworthy. Having any extra 'seaworthiness' is unnecessary and will compromise other aspects of the design.

I have just read a brief account of Richard Wood's (successful multihull designer) having to abondon the cat that he lived aboard. He has accumalated 20,000 miles on the boat, which was his own design, before getting caught in a huge storm. Despite laying sea-anchors etc he finally decided that he would be safer in the life raft than on the boat so took the decision to abandon his uninsured boat. In the end, his boat never did capsize, so he could have stayed aboard, but the point is that this hugely experienced sailor, sailing a boat of his own design, underestimated the seaworthiness of his boat. It is not an easy subject!

 

Thank you! I think that is one of the clearest posts I've read in this thread. I shall now be able to re-read the thread with a good idea of where you are coming from.

As I've stated before, I think I probably agree with you for the most part. It was hard to come to that conclusion without knowing a few specifics. I understand some of your reluctance to post specifics, as soon as you provide a number, someone might try to find an exception in an effort to score debate points. If your idea of heavy = good was D/L 350+ and light = bad was D/L < 250, we have an argument. IMO your choice of D/L 100 as light is quite valid for a cruising boat, and after this post I can see that "moderate" means much the same to both of us.

As I said in another post, I have to thank you for getting my to look hard at ocean racing boats. I was looking for data to support my feeling that speed = safety to a great extent. I still feel that way, however, I have come to the conclusion that the speed can only come from size (LWL), since no evolution of design (that I can find) has substantially increased the S/L ratios of moderate displacement boats.

If I want 200 miles a day, I'd best get a Deerfoot, not a Pogo40.

Thanks again, I apologize for the provocative posts. Those were debate, not discussion.

Randy

 

Sorry if I have not understood your boat preferences.

I find the boat you are referring to very beautiful and a very fine boat. If I were a rich man I would also like to have one of those. It is only "classical" above the waterline. I would never have thought that the type of boat that you would like to own would be a modern designed boat with a modern hull.

I would never have thought that you would chose a boat with a semi-balanced spade rudder and a Fin keel with a bulb. Or that you would chose a performance boat, with a 22 SA/D (the good old guys would call that a racer) and a 175 D/L (the same Guys would call that a light displacement racer). I have the distinct impression that, if I look in other threads, I will find that this was not properly the kind of boat that you advocate as a cruiser but, who cares... I am happy that you think this way.

But if you think that this boat has a high AVS (I mean, the ones over 140, the ones I thought you liked) you are wrong. I think this boat is not very far away, in what concerns the type of stability (GZ curve) from the Sweden Yacht 42, a boat that I have posted in “my” thread about cruising (last post).

http://www.boatdesign.net/forums/showthread.php?t=11479&page=27

I have said about the SW42: “They are faster than the Malos and if I could chose I would have the 42 instead of the Malo 40. The 42 is probably the most beautiful boat I have ever seen (interior and exterior)”.

It looks that after all we have identical tastes regarding cruising boats.

I will post pictures of “your boat” and from the sw42. You can see that they have a very similar hull, similar bulbed keels and spade rudders. The SW42 is more on the cruising side, even if it is considered a good ocean cruiser-racer. It is a much less “radical” (as the old Guys like to call these kind of boats) than “Your” boat. It only has a D/L of 209 (“your boat” boat has 175) and a SA/D of 19.3 (“your” boat has 22.4).

Guillermo, I have to say that you really surprised me with the kind of boat you would like to own. I would never guess: a modern, fast and light boat with bulbed keel and spade rudder... WOW!

Perhaps now we can work more constructively. I am sure this size of boat costs more than the vast majority of people can afford.

It would be very interesting if you (or Mike) could chose a seaworthy sailboat that costs about the same as the POGO. I mean a production boat (even a small production one). Certainly in the world market (new boats) there should be at least one boat that you can find seaworthy that costs about $230 000 US dollars.

Chose that boat and then we will make a comparison with the Pogo, regarding STIX, AVS, stability curve, Gz at 90º, positive stability and inverted stability and then we can reach some conclusions about both boats seaworthiness.

 

I said I've leave this thread, but can't let this go by. After reading the Coroner's report into Rising Farrster again, it's obvious that;

1 -Farr designed the Farr 11.6/38 in 1978 with no bulb. Dozens have been built. The only one I know of to have been lost hit the bricks in a severe gale or cyclone.
2- Binks remodelled the boat into the IMS 38 with bulb keel. Farr produced plans for the new frames by way of keel (Drawing 21). ABS approved them. I can find no evidence that "no engineering analysis was done".
3- Binks built Rising Farrster. The hull shell was NOT built to the drawings but was thinner than it should have been.
4- Binks then added 140kg to Rising Farrster's keel bulb AFTER CONSTRUCTION.
5- At this stage, AFTER CONSTRUCTION, someone (probably Binks) produced drawing 21A showing reinforcement for the heavier keel, and got approval from ABS. However, the modified structure was NOT built into Rising Farrster which therefore had a heavier keel with NO reinforcement.
6 - ABS' scheme for keel bolt washers was probably inadequate.

The Coroner specifically did not bring Farr into question. The boat was unsafe because of ABS's deficiencies, the fact that it was not built to plan, and the design (although the Coroner did not mention whether the "design" problem was that the boat was not designed to take the heavier bulb).

God knows why anyone would skimp on construction around the keel floors, but it seems a bit unfair to use an incident where ABS was deficient and a boat was not built to design and was then given a heavier bulb without being reinforced, as an indictment of the Farr office. They did not know the boat was not built to design; they did not (it appears) know of the heavier bulb being fitted; they did not know (it appears) that the reinforced floors for the heavier bulb were not fitted.

Mike, if I bought a design from you, failed to build the hull as thickly as it should have been, then modified the boat without (apparently) your knowledge and approval and deaths resulted, would you like it if you received the blame on internet forums?

I know ABS is only a guide, but it's yet another case where the conventional wisdom has been found to be deficient - in the case of ABS, not just in keel bolts but in slamming loads and decks.

 

Chris
Thanks for the correction I've been labouring under that delusion since I read a synopsis of failed scantling rules by David Payne last year. I had not read the coroners report. I was looking for a poular yacht designer to illustrate the point. Apologies to Farr.

There are some great stuff ups in the both the military and the commercial shipping world that would have been a much better examples (the danger of trying to popularise). I would have liked to have used a common yacht hullform example but was shy of the argument that would produce, that something broke so catastrophically was a simpler illustration.

In the case of the relevant ABS scantlings above I think Sparkman and Stephens had the biggest input into the formulation .

I am curious , what is your opinion, do you consider that any of the yacht design stables have ever producing an unseaworthy boat?

Modern scantling rules are still a trap for people without a solid technical background. Modern changes to the rules are often with the benefit of not only hindsight but also more experience in FEA (computer stress modeling). Earlier experiments with Naval vessels and strain gauges showed that stresses were far higher in certain parts of the structure than had been designed for, these stresses show up very clearly in a good FEA analysis. It is not the "experts fault" it is complex. Everyone will be aware of the abysmal and catastrophic failures of some of the America's cup boats despite all the modern computer tools, master designers and endless amounts of $$.