Re: [PSUBS-MAILIST] Pressure hull materials

[Dale Raby <publisher@thegreenbayweb.com>]

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On Sunday 22 December 2002 10:08, you wrote:

Well, I'm not actually convinced it wouldn't work just yet... but it 
certainly needs some development.  I'll see about developing a small model 
and/or some drawings.  If it can be made as a bathtub sub, I see no reason it 
woldn't work on a larger scale.  I had not envisioned something that could be 
collapsed, though.  There would be too many things that would have to be put 
inside it that might not be flexible... drive components, for instance, and 
then there would be a fairly heavy chunk of balast material.  

Is there a place to post photographs... just on the odd chance I am able to 
construct something that works and is "photogenic" enough to put on public 
display.

> Actually someone brought up the concept of an inflatable ambient sub just
> recently, and we were visualizing folding it up and storing in the trunk of
> a car after the dive. Cool! The problem I see with this concept is that
> although the hull might be light, this does not mean the sub as a whole can
> be light too -- it still needs overall to be the same density as seawater
> if you want it to sink. One can argue you could then put the weight saved
> from the hull into more useful things like batteries. But that's going to
> be one heck of a lot of weight to connect structurally to the flexible
> material. One way or another you're flexible material will end up
> supporting it, regardless of whether you use some sort of exostructure.
> Maybe this would work if attempted on a very small scale, to keep the hull
> volume down, such as a ride-on scooter for divers. 
 
> I hate to counter innovative ideas... keep them coming!
>  
> cheers,
>  
> Alec
>  
>  
>  
> 
> 	-----Original Message----- 
> 	From: Dale Raby [mailto:publisher@thegreenbayweb.com] 
> 	Sent: Sun 12/22/2002 9:59 AM 
> 	To: personal_submersibles@psubs.org 
> 	Cc: 
> 	Subject: Re: [PSUBS-MAILIST] Pressure hull materials
> 	
> 	
> 
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> 	Good Morning:
> 	
> 	I am new to the list and not very well versed in the subject, though I
> have
 to say that I find the topic of your discussions fascinating.  On the
> subject of pressure hull materials I have a few thoughts.  Perhaps someone
> with more knowledge/ability/money can make use of it.  If nothing else...
> perhaps it will provide you with some amusement.
> 	
> 	The basic function of a hull, as I understand the concept, is to provide
> a
 "bubble" of air for the occupants of the submarine to breath.  Now, if
> you want to maintain an atmospheric pressure similar to that found at sea
> level, you need a very rigid structure because the water pressure at depth
> will tend to compress the shell.  If one is not concerned with this, the
> hull's rigidity is not at all a concern.  Bubbles can form in great depths
> with nothing but the surface tension of the water to hold their shape. 
> 	Now, suppose someone were to form a thick clear flexible plastic "bubble"
> 	with a conventional rigid hatch and seal for entry/egress.  One could
> 	concievably use an old water bed mattress.  As the "bubble" descends, the
> 	non-rigid hull would compress.  One could equalize this pressure by
> 	compensating with bottled air.  You would have to have a pressure valve
> 	somewhere to keep the bubble from bursting from internal pressure.
> 	Equalization could be maintained by simply opening the valve whenever it
> is
 noticed that the hull is collapsing until air bleeds out through the
> pressure valve.
> 	
> 	The craft would have to have a light framework to affix things to... life
> 	support components, electrical devices for light, etc.  It would be not
> 	unlike a semi-rigid dirigible... and the bottom of the craft would have
> to
 have some ballast to maintain equilibrium as well as to allow it to
> sink below the surface.  Variable ballast tanks could also be formed from
> the same stuff... though they would function more as "anti-ballast" tanks,
> since it would be the absence of air that would cause the device to sink. 
> 	One obvious drawback would be the necessity of decompression... and I
> suspect
 that there would be a very definite absolute depth limit... maybe
> a hundred feet... but in small lakes and rivers, that would be sufficient. 
> You'd have to watch your time, just like a SCUBA diver, and come up slowly,
> allowing the overpressure to bleed out.
> 	
> 	For a model, a zip-lock plastic bag would suffice.  Put a CO2 cartridge
> 	inside it with a valve assembly for equalization experiments.
> 	
> 	One other question....  Bushnell's Turtle as well as the CSA Hunley
> utilized
 simple muscle power for propulsion.  They didn't have electrics
> or internal combustion engines.  Has anyone postulated a modern Hunley that
> would use the same type of propulsion?
> 	
> 	OK, go ahead and laugh at me.  I'm sure I've said more than a few amusing
> 	things... but if my flexible hull concept is flawed, I would like to know
> why
 it wouldn't work.
> 	
> 	- --
> 	Dale A. Raby
> 	Editor/Publisher
> 	The Green Bay Web
> 	http://www.thegreenbayweb.com
> 	Nothing is ever so bad that it couldn't be worse, and if it could be
> worse,
 then maybe it's not so bad!
> 	
> 	
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- -- 
Dale A. Raby
Editor/Publisher
The Green Bay Web
http://www.thegreenbayweb.com
Nothing is ever so bad that it couldn't be worse, and if it could be worse, 
then maybe it's not so bad!
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