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The US Navy has repeatedly looked at FRP for torpedo and other hulls
over the years. Hull water absorption, hull weeping, loss of structural
strength with a minor ding, inability to repair vessel and maintain pressure
rating, inconsistent pressure cycle lifetime, and difficulty in conclusive NDT
were issues that turned the Navy away from this material for pressure hulls.
A small un-noticed hull ding will act as a focus for hull stress under
pressure and can result in buckling or catastrophic failure well below the
calculated crush depth. We just had a horizontal 30K gal. end-core balsa FRP composite water
tank buckle a few weeks ago, not a pretty picture when it happened and no
indication on the outside that failure was imminent (the tank had just been
inspected inside and out 4 months previously). FRP would be fine for an
ambient sub but would not be comfortable using it for a 1-atmos. PSUB. Respectfully, Jay K. Jeffries Andros Is., It is the mark of an educated mind to be able to entertain a thought
without accepting it. - Aristotle -----Original Message----- Somewhere in the psubs archives (under one of the conventions), there
is an ABS spreadsheet for performing this calculation on metallic cylindrical
pressure vessels. It is quite comprehensive in it's analysis, however FRP, unlike steel, concrete, and even wood, seems to have less history, and available data
in its use for 1 atm pressure vessels. If memory serves me correctly, the
Busby manual references one as a shallow water test bed. FRP, is a fabulous material for ambient subs for all the playing around
you could do in complex shapes as demonstrated by http://exomos.com/exomos_main_content.html When I finish my marine studies, I will look at using FRP for designs
along the lines of my original concept http://www.frappr.com/psub Joe >From: DrewBane1@aol.com >Reply-To: >To: >Subject: [PSUBS-MAILIST] hull thickness technicial help needed >Date: Tue, 17 Oct 2006 15:35:01 EDT > >I have the technical spec's on a 1/4" laminate using
conventional lay up... >Is there anyone out there that can derive from this tech info a
safe depth >for >a frp submersible? >resin
type
411 8084 >flexural strength
psi
29,600 39,0000 >flexural modulus x10>5psi
10.3 12.7 >tensile strength psi 20,700
31,500 >tensile modulus
x10>5psi
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