How to calculate a sail catamaran hull pressure?

Hi Alik

Can you be more specific, as i'm still not clear what is unfriendly to vessels below 24m.
Most of the list you gave, is standard for all Classifications I have worked with, thus trying to understand what is different about GL to DNV.

 

So far, GL2012 is the best for small composite craft and allows to design weight efficient structures. We have done many patrol boats <24m under these rules, just because it is the best. More detailed analysis will require us making table of comparison (quite time consuming work), so the best is just to read the rules GL2012 and compare.

We need to estimate two main criteria, for any rules:

a) Small craft mean small budgets, including design budget that should match the construction cost of the craft. In these terms, one can look at design load cases and imagine the amount of engineering hours. This also includes testing of laminates - not affordable for most of small craft projects due to cost of testing.

b) Ability to produce lightweight and efficient structures, without dumb limitations on min thickness, materials use, reasonable design loads and safety factors, etc.

c) Safety, but I would say structural damage on small craft is extremely rare event with very low significance, excerpt the cases of collision which are not covered.

 

Alik,

I appreciate what you're saying, but other than a personal preference for GL, i'm still not clear what is different between DNV and GL for vessels under 24m that you cite as being unfriendly. Hence seeking further clarification between the two.

 

I agree with Alik that develop this comparative study and these explanations require too much work for anyone to be motivated to carry it out. Moreover, the expression "friendly" is very subjective and it is possible that nobody is able to explain it objectively. Something can be friendly to my, because I have a certain knowledge, and for you, that you do not, be very cumbersome and conversely.
No positive discussion, imho.

 

You're missing the point.

To state that Classification society A is better than B can only be made knowing the in's and out's of each Class society, i.e both its good and bad point for a basis of comparison. Otherwise how can one qualify such a statement? Thus it then becomes subjective rather than objective in the absence of such qualifiers.

I come across far too many surveyors that like to impose "their" views for me to comply with them, to get XX or YY approved. I'm not interested in their personal views or someone's feelings on the matter...i only care about what is written in the rules for compliance - it is simply a pass or fail. Anything else is subjective.

If there is a difference of opinion, that's fine -it is thus just an opinion not fact-, but it can only be made once the differences have been outlined, ergo back to what is the basis for comparison, is it personal view or a factual view. That's all im trying to ascertain.

 

OK, OK, you are quite right in everything you say but, if I were Alik, will not use my time on such explanations. Once raised the doubt by Alik, who wants to investigate further or seek expliaciones, can do on his own. Especially if, as I suppose that happens to you, have enough knowledge to do so.
Cheers.

 

TANSL, exactly correct. I better do some weekend sailing rather than doing quite extensive comparison studies to satisfy forum members. I have experience and express my opinion, and give the idea why I think so. The detailed report is not foreseen...

 

Thanks for the clarification Alik, it is an opinion only.
That's all I was after.

 

Yes, everything I write here is an opinion. Professional opinion supported by years of practice and about 90 our designs built, about 50% of them in composite.

The same refers to Your posts - opinion as well. Good professional opinion.

No one's writings can to be treated as a dogma

 

All the shades of grey

I wonder why Asterix's dog was named Dogma-tix... may be "he" was a bi tch ?

LOL. So one becomes a professional when you get all the calculations right, take a few steps back and re-evaluate and reconsider certain aspects that you feel is inadequate from experience contrary to the calculations. You make the changes and everything works out, the music plays and the boat sails off into the sunset on perfectly calm waters.

 

In the formulas regulations of classification societies have to calculate scantlings, there are many factors that have been defined based on the practical experiences of the society, its inspectors and its technical teams. So, believe it or not, you are right: we must calculate, step back for observing reality, and recalculate.