Re: [PSUBS-MAILIST] Fiberglass hulls

[Marc de Piolenc <piolenc@archivale.com>]

On 6/4/2010 8:52 AM, greg cottrell wrote:
> Hello Marc,
> You make some excellent points. I learned a few things that I didn't
> know about composites . However, in my defense, I'd like to say:
> (1) I agree that psubbers have the smarts to "work" with composites. My
> comment was about being able to do the design/ engineering on an all
> composite sub.

Composites design is not rocket science, either. In the fifty-plus years 
that fiber-reinforced composites have been used industrially, the 
literature on them has grown and design procedures have become well 
established.

> (2) The American Bureau of Shipping will not even consider certification
> of a composite sub at this time because of unknowns.

I'm afraid that says a lot more about the ABS than about composites. 
There are no significant unknowns - composites have been used for 
pressure and vacuum vessels and for every other conceivable application 
for years - so what this really means is that the ABS has not taken the 
time to get up to speed on this material system. That's too bad if your 
design requires their certificate, but it says nothing about the 
material - only the certification authority.

> (3) I respectfully disagree with the statement that compressive
> strengths in textbooks have "absolutely no relevance to our work". I
> would argue that resistance to yielding is equal in importance to
> resistance to overall buckling in submarine design.

I said "in practical structures." One could conceive of a 
compression-loaded structure that reaches its material yield point 
before buckling, but it would have no use in the real world. In 
thirty-plus years of taking an interest in structures I have never found 
a practical example of this. If you know of one, I would like to know 
about it, too.

> (4)/ Generally speaking/, strength to weight ratios and exotic materials
> become more important in subs that operate below 2500 ft.
> Even though I built all the molds and fiberglass fairings for my sub
> myself (and am currently building fiberglass fairings for another sub) I
> would not attempt to use it for the hull.

De gustibus non est disputandum. I can't argue with a personal preference.

Marc



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