[PSUBS-MAILIST] dual hull??

[jbarlow@bjservices.ca]

I sent to the wrong address before, but I'm still curious.


----- Forwarded by James Barlow/BJSCAN/BJSERVICES on 29/01/2003 05:54 PM
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                      James Barlow                                                                                                     
                                               To:       owner-personal_submersibles@psubs.org                                         
                      29/01/2003 10:31         cc:                                                                                     
                      AM                       Subject:  Dual Hull Concept                                                             
                                                                                                                                       
                                                                                                                                       



I'm just thinking out loud here..

If you have a 36" [914.40 mm]OD x 0.500" [12.70 mm] WT outer hull and put
inside a 34" [863.60 mm] OD x 0.500" [12.70 mm] WT inner hull. ( leaving an
annulus of 0.500" per side) and fill that area with hydraulic oil that you
pump up to some high pressure.  The pressure is equal everywhere but the
area on the outer hull is greater, resulting in a net force outward.

36 - 0.5 -0.5 = 35.000" ID  [889.00 mm]

34 OD of inner hull = [863.60 mm]

If the was 100 psi oil pressure in the annulus area then the force out
would be:
100 psi x 355/113 (pi) x 35.000" x length = 3500 pi x L pounds
[7.030696 kg/cm2 x 355/113 x 88.900 cm = 625.029 pi X L ]

 force on inside would be:
100 psi x 355/113 (pi) x 34.000" x L = 3400 pi x L  pounds
[7.030696 kg/cm2 x 355/113 x 86.360 cm = 607.171 pi X L]

a direct ratio of diameters. (id outer / OD inner)


If you are 100 psi deep (6.80 atm (217 feet [66 m])
then the outer hull would see 2.8 psi differential.  (ratio of 36" / 35")
(OD/ID of outer hull)



Negating yield of outer hull due to increasing inner (which you can't do
but maybe you would want to fill with a compressible gas like nitrogen
instead of oil) the inner hull sees the same 100 psi, but the outer sees
outside pressure less roughly 100 psi.

Did I miss something??


Of course you essentially have a 33" [838.20 mm] ID Hull now...  and one
that weighs essentially the same as a 33" ID [838.20 mm] x 1" WT [12.70 mm]
hull.


The pressure rating of such a hull would be great anyway.  However perhaps
as the inner hull only sees 100 psi and is protected from mechanical
damage, it could be made from fibreglass or some such material to save
weight.



All the numbers above are only just numbers I threw in for illustration.
It wouldn't have to be a 1/2" wall thickness hull.



Not to start any wars, I'm not advocating the use of dual hulls.  Just
curious...
Comments?

Jay.