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[PSUBS-MAILIST] Glass as a viewport material?
I recently saw a post suggesting glass as a viewport material for Psubs.
Although there are many reasons that glass was rejected early on for manned
submersibles, one of those reasons is quite interesting. There is a form of
failure that can occur in glass that has never been fully understood.
Basically, a viewport can sometimes shatter after pressurization when the
pressure is being released. It can sometimes occur at a relatively shallow
depth. The failure appears to be from a build up of tensile force. Somehow,
energy is stored in the material and released suddenly when most of the
pressure has been removed. This can be seen to happen occasionally in glass
buoyancy spheres. It can also happen to acrylic but, if I remember
correctly, only during rapid decompression. In glass, it can happen during
slow decompression and without warning. I think that Jerry Stachiw briefly
mentioned this in his book but I don't remember exactly which page.
George Kittredge once told me about some tests that he was aware of using
glass spheres that went to great depth and then shattered near the surface.
At any rate, Acrylic remains the most thoroughly tested and best understood
material for PVHO applications.
Greg Cottrell
Project Manager
greg@precisionplastics.com
http://www.precisionplastics.com
P please consider the environment before printing this email
-----Original Message-----
From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org] On Behalf Of Marc de Piolenc
Sent: Wednesday, September 29, 2010 11:19 PM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Electric Propulsion
Underwater the main component of drag is viscous, so drag is
proportional to the square of the speed, and power required is
proportional to the cube. So to triple your underwater speed from 10 to
30 knots requires twenty-seven (three cubed) times the power. This is
not a feasible undertaking unless you provide a completely separate
power plant with a very concentrated power source - maybe a Walter
hydrogen-peroxide turbine. Just sizing your electrical installation for
this power range is impractical.
Marc de Piolenc
Archivale catalog: http://www.archivale.com/catalog
Polymath weblog: http://www.archivale.com/weblog
Translation services: http://www.proz.com/profile/639380
Ducted fans: http://massflow.archivale.com/
On 9/30/2010 10:18 AM, Firebolt wrote:
> Hello Again thanks everyone for the shaft seal info, I appreciate it. I
> am down to only a few more things I need to know, the electric motor.
> For me I will want to travel at a speed of 10 knots under water
> _but_ I would like for there to be a possibility for me to go faster,
> say, 25 to 30 knots. I know it depends on the dimensions of the sub, it
> will most likely weigh 50 tons since it is 60 ft and 10 ft inside
> diameter. this is not a cylinder shaped sub though
> if you want a picture I will give it to you just tell me. I thought
> about a 70 kw motor but I don't know if it will give me the speeds I
> want. And if you can, I want to know what the best battery would be to
> power the sub with lots of electronics and appliances (TV's, microwave,
> water pumps etc.)
> I await your assistance.
> John
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603-529-1100
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