Seaworthiness

Of course, but that is not the point. The point is that there are many people out there who actually see the STIX number as a quantitative measure of how safe a boat is :!:

Mikey

 

And that is why boats that don't sink should have higher STIX ... because they are safer.

 

Originally posted by RHough
"Real common sense tells us that NO boat is "safe". No matter what the STIX number might be. As soon as you can divorce yourself from the idea that a small boat can be made "safe", you can begin to see how any narrow-minded focus on one aspect of design will lead to false conclusions."

I think this statement by Randy should be given some thought. I see all too often an oversimplification of known facts, with a disregard to unknown facts in order that a conclusion may be derived that supports ones own arguments. The fact that there is no set standard, no agreed upon measure of seaworthiness makes it impossible to verify that a conclusion is false. It may be instructive to not draw conclusions, but to take a look at facts, and pounder the breadth and depth of their meaning, or their influence, and correlate them with other known variables. In a way STYX does this, but to rely on one system of measure as a be all end all formula is nonsense.

 

I agree, and adding an U after the quantitative measure of safety number, as many potential boat buyers see STIX, does exactly that

By the way, thanks for educating Jack, the potential boat buyer, that STIX stands for STability IndeX, now You only have 99,999,999 people left to educate

I want to show both pieces of information, in order of importance as I see them. I and Randy have aired our view, now it is others turn to do the same.

Mikey

 

Thanks Tom,

As a sailor of an "unsafe" boat that has never failed to bring me home, I find it quite amusing that engineers think that they can somehow make the sea safe for fools in small boats.

How about requiring all CE "Ocean" rated boats to be unsinkable? I wonder how many poster's pet boats would be eliminated?

Randy

 

I must admit, as the thread progressed, I thought we would all agree on what the charecteristics of a POGO type boat are, compared to a more traditional cruiser. Surprisingly, however, there has even been some disagreement about this. This is what I see as fact: The pogo is faster, has higher initial stability, higher AVS and requires more energy to capsize. It is also unsinkable, but this is not a function of its hull form, so similar designs would not necessarily be so. On the downside it has faster roll accelerations (which studies show leads to motion sickness), will re-right less easily and will probably be noisier and generally less comfy. The difference of opinion mostly seems to come down to how to interpret that information, which is because personal priorities differ. Some see quick passage making and a large area under the GZ curve as most important, others believe a small negative GZ area is the most critical thing. To an extent, the order of priorities changes with the type of sailing involved (coastal, blue water, racing etc), but within one genre of sailing, say blue water live aboard cruising, it ought to be possible to agree a set of criteria and priority order. It is an interesting question whether pre-event or post-event attributes are more important. Certainly prevention is better than cure, but we all get poorly sometimes...
I have some sympathy with RHough's point that crew skill (or lack thereof) is vitally important. However, it is the responsibility of the designer to minimise the impact of crew error (on a cruising boat).
As I have said before, I think it is important that boats meet some minimum standard of seaworthiness for the intended use. However, designing a boat which significantly exceeds that minimum standard is not really worth it. I for one, would trade excess safety for more speed, more space, better looks, cheaper construction etc, and I don't think I'm alone.
The fact that the pogo is unsinkable is great, but sinkability is a seperate issue to stability and therefore I think seperating it from STIX (STYX seems very Freudian!) is a good idea. I like the 'U' idea.
So don't be disheartened Jack, most of us agree on the physics - just not how to make best use of it! But that's the fun of boat design.
ALL design is a compromise. The Pogo is better at some things and worse at others. It is up to the buyer to decide whether the good outweighs the bad.

 

Well, to the other group we could add many hundres of NA's, engineers and designers thinking in a similar way we do. Among them probably we could include the working group who developed STIX, formed by most reputed professionals from well stablished organizations such as RORC, etc. Those people developed a system that penalize excessive beams and light weights for the recreational market. And they did the thing after analyzing a huge database of boats as it has already be explained (see post 205 at the STIX thread, i.e.)

Excuse me, but the thing is not like that. I deduced the delta value, just to be able to compare geometry and weight related stability issues between Pogo and other boats not having unsinkability properties. That's all, and I think it's fair. Nobody is denying here unsinkability as a safety bonus. For sure it is.

The development of the STIX is precisely a big effort to try to assess some important aspects of seaworthiness. Everything is measurable and quantificable, including seaworthiness. STIX is a magnificent intent and my only worrying is it, in my opinion, still has dark aspects that need to be improved, precisely to make it more accurate. Aspects as transverse inertia, loss of stability due to speed, roll damping ability, negative/positive ratio of areas under the GZ curve, course keeping ability, etc., still have to be incorporated, from my point of view.

Excuse me, but you seem to have little knowledge of what NAs, designers and engineers formation at schools and universities is nowadays. People like the NAs and designers you mention have also been formed in such places.

And if you are convinced that when cruising you cannot get into tight situations where speed is not possible, then you'd better check yours...

Absolutely on the side of Finot. About Pogo 40, I still would like to wait some years and a couple of hundreds of Pogos cruising around there to say so.

By the way: It seems Pogo 40 is somekind of my "bestia negra" (I don't know how to translate this into english) but it is not. It's only an excellent example to be brought to discussion and analysis, precisely because of its most interesting radicality. That's all. If I were the designer or builder of this boat I would be quite happy and proud of seeing how she is able to give foot for such a long and passionate discussion.

Cheers.

 

Yet their system gives the Pogo a high value.

The science of boats was developed from the study of practical boats that worked, just as the science of flight was developed from things that fly. Much of the early scientific "facts" of flight have proved wrong. The theories and formulas were developed from empirical testing. The engineers and designers using data from towing tanks made some monumental errors, Brit Chance's Mariner is a prime example. I think it is more than likely that when any group starts from an existing sample of boats and creates a set of evaluation criteria, it can be very valid for the sample. When used to evaluate designs that are far from the norm, the evaluation becomes suspect. This is shown by the failure of every rating rule to date. IOR did a dandy job of rating existing designs when the rule was written. It does not do such a great job when applied to modern boats. Like racing rules, STIX is type forming. If a clever engineer/designer had a need, they could probably design a boat that was very unsafe but would have a high STIX number. This is a basic flaw in rules based on existing boats.

Getting into that tight situation is the pre-event. Have you noticed that the more experienced a sailor is the fewer times they find themselves in such situations?

If we can agree that all voyages include some risk, then we have to discuss what level of risk is acceptable. Each person should do all they can to keep risk within the limits they are comfortable with. I think the probability of an event that would lead to sinking is more likely than an event that would lead to capsize. My evaluation formula would place unsinkable boats with collision bulkheads higher on the scale of relative seaworthiness than boats with high AVS. Empirical evidence shows that small boats can make safe passages. 1,000's of voyages in boats that do not have high STIX values tells me that using STIX as the sole criteria for determining "seaworthiness" does not fit well with experience.

This is the attitude of many engineers. While I would like to agree, and do agree in theory, the fact is at this point in time seaworthiness is NOT measurable and quantifiable. We cannot even agree on the definition! The need of engineers to measure and quantify things is shown very well in the cars we drive. Rather than concentrating on reducing crashes, they concentrate on reducing injury after the event. IMO STIX or any other evaluation that does not consider the skill of the operator is of limited value. Relying on a boat or car to protect you after you crash or capsize and not considering the vehicles ability to avoid the situation in the first place is not logical. It pleases engineers, because post-event engineering is indeed measurable and quantifiable.

Take care,

Randy

 

In English, we say it is your 'bête noir'.

Perhaps 'FcFc' can let us know the French equivalent.

 

Not so high. A non-delta STIX of 36.3 (if it is so) for the geometry and weight related factors (pre-event) for a 40 footer is not that high. I'd even dare to say it is quite dissapointing, generally speaking.

If we could add more factors to the STIX, as the ones I talked about at post 592, it could be very well possible for Pogo 40 to reach a higher non-delta value. How about that?

I agree and I have said that several times at the STIX thread. That's one of the reasons I think it's necessary to improve STIX (Crag is more inclined to make the thing simply dissapear, which could be the other way of doing things if we do not arrive to a more accurate and satisfactory STIX definition).

I think you're contradicting yourself here.

Cheers.

 

Thanks, Crag

Cheers.

 

Given the degree of input of the RORC into the formulation of STIX, I am suprised that the adjustment made for having fully integrated buoyance is '5', as they only ever allowed '2' when computing its forerunner, the SSSN.

 

Just read at Yachting World: "Berrimilla", a Brolga 33 launched in 1977 to a Peter Joubert design, and crewed by veterans Alex Whitworth and Pete Crozier, suffered a 180º capsize and dismasted when sailing under bare poles in a 50+ (gusts) knots gale. Last year Berrimilla competed in both Fastnet and Sidney-Hobart races. They were coming back from Hobart. Boat was receiving waves from the port quarter, when a big beam wave hit the boat on that side, knocking her down. Crew is injured but safe and made it to Eden, firstly motoring and then towed.
Anyone has more info?

http://www.berrimilla.com/
From there: "Joubert’s boats have a reputation for extreme toughness and seaworthiness and Berrimilla is very strong, heavily built and seaworthy and we have sailed her through some atrocious weather. Her stability index is 141.6 (IMS) and her calculated limit of positive stability is 135.4 degrees. Both of these are very much higher than most modern boats and quite reassuring in big breaking waves."

 

Another one rolled and dismasted, "Privateer" crewed by solo sailor Ken Barnes:
http://www.msnbc.msn.com/id/16457498/

 

Like this one:
http://www.youtube.com/watch?v=zk1o6MgfzrE

The boat: Swedenyacht 390 http://www.swedenyachts.se/