[PSUBS-MAILIST] buoyancy

[Alan James via Personal_Submersibles]

Hank,I did a quick calc on a sphere of nominal dimensions made of epoxy / fiberglass.With external pressure it had a depth of 4347ft, with internal 3785ft. I should have postedthe results in psi, but you get the picture.The big thing to me would be that if you ruptured it by hitting anything, or so it failed, you would go downlike a lead balloon. Alan
      From: Alan via Personal_Submersibles <personal_submersibles at psubs.org>
 To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
 Sent: Thursday, November 12, 2015 7:23 AM
 Subject: Re: [PSUBS-MAILIST] buoyancy
   
Hank,in general, from memory, the fibreglass products I put through mypressure program, had similar external pressure resistance to the internal.However the carbon fibre had better tensile strength than compressive strength.If your tanks are rated to 3,600psi they probably have a 4  x safety factor ( you could check that), so may crush at 14000 psi or 28,000ft. looks like a big safety margin. I am putting in a positive comment here butobviously that would need verifying.Cheers Alan

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On 12/11/2015, at 2:33 am, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:


I was thinking about using CNG (compressed natural gas)  tanks for buoyancy.  The type 4 tanks are carbon fibre and rated for 3,600 psi and very light.  My idea was to keep the tanks full of compressed air so they can withstand the sub depth rating plus a safety margin.   I am liking trawl floats may be better now because they are rated high enough and not air filled.  The CNG  tanks are much cheaper and conveniently shaped.   Hmmm not sure now.??Any thoughts or concerns anyone????Hank

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