[PSUBS-MAILIST] Deep sea question

[Vance Bradley]

I don't recall the specific mix for Alvin. You are right of course for comparable wall thicknesses, but the way I understand it from tabletop descriptions, steel compresses more. The Mirs are maraging steel and have seawater vbts to compensate buoyancy variables. The new Alvin iteration is equipped the same way. The Ti sphere Is 3.5" wall, I think, which I speculate to be effectively non or near noncompressable for the given operating pressure of 11,000 psi. Or so the story goes.
Vance

Sent from my iPhone

> On Apr 14, 2014, at 7:21 PM, "Sean T. Stevenson" <cast55 at telus.net> wrote:
> 
> Vance - that doesn't seem accurate.  Compressibility of a material is the inverse of its bulk modulus.  For ASTM A516 grade 70 carbon steel, the bulk modulus is 140 GPa, and for ASTM B265 grade 5 titanium it is 110 GPa.  So the steel actually performs better in that regard.  Was the Alvin sphere made from some atypical alloy?
> 
> Sean
> 
> 
> From: "Vance Bradley" <VBra676539 at AOL.com>
> To: "Personal Submersibles General Discussion" <personal_submersibles at psubs.org>
> Sent: Monday, April 14, 2014 4:03:39 PM
> Subject: Re: [PSUBS-MAILIST] Deep sea question
> 
> Alvin carried steel drop weights which were dropped at depth. The new system is like the Mirs and the Pisces before them-- vbts and high pressure pumps. Titanium hulls don't compress at depth so are actually more buoyant at 20,000 feet than at the surface due to increased water density. All that has to be taken into account.
> Vance
> 
> Sent from my iPhone
> 
> On Apr 14, 2014, at 5:57 PM, <swaters at waters-ks.com> wrote:
> 
> I have a question I have never understood about really deep sea submarines. How do they go up and down?
> Submarines that use compressed air at 3,000 psi like ours could only go so deep before the water pressure is to great for the HP air. What do submarines like Alvin do? This is probably a really stupid question, but I have never understood it.
> Thanks,
> Scott Waters
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