From: "Jay K. Jeffries" <bottomgun@mindspring.com>
Reply-To: personal_submersibles@psubs.org
To: <personal_submersibles@psubs.org>
Subject: RE: [PSUBS-MAILIST] hull thickness technical help needed
Date: Tue, 17 Oct 2006 21:25:19 -0400
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., Bahamas
It is the mark of an educated mind to be able to entertain a thought
without
accepting it.
- Aristotle
-----Original Message-----
From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org] On Behalf Of Joseph Perkel
Sent: Tuesday, October 17, 2006 8:50 PM
To: personal_submersibles@psubs.org
Subject: RE: [PSUBS-MAILIST] hull thickness technicial help needed
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: personal_submersibles@psubs.org
>To: personal_submersibles@psubs.org
>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 17.4 14.4
>
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