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Re: [PSUBS-MAILIST] Pressure hull

Thijs,
 
Even though this hull design is very different from the normal PSUB hull, it does have a number of nice features.  It fits well with a streamlined FRP outer shell in that it presents a smaller projected area to flow relative to other hull shapes that will accommodate a seated pilot.  For it displacement, it also has good freeboard and might actually make it possible to meet the ABS 2.5 ft (76 cm) minimum freeboard rule for a small boat without destroying the hydrodynamic lines of the boat.  The viewport locations are great for forward and downward viewing. Side viewports could be easily added to improve port and starboard visibility  Because all viewports are flat, the cost becomes manageable for a PSUB.  Orientation of MBTs are going to take some thought in order not to have the CB of the boat to close to the bow.  I am not sure I would go with mild steel for hull.  You should be able to find off the shelf torispherical endcaps made of a higher yield point steel such as A516, Gr 70 or something equivalent without significantly impacting the hull cost.  I agree with Alec that it would be a good idea to run an FE analysis of the hull including viewports to get a better handle on crush depth.  I am not sure the ABS equations to calculated hull stress are applicable given such a short cylindrical section.
 
I for one like the hull.
 
Cliff
----- Original Message -----
From: Thijs Struijs
To: PSUBS
Sent: Sunday, February 09, 2003 11:02 AM
Subject: [PSUBS-MAILIST] Pressure hull

To all,
 
I would like some reactions on a drawing i made a while ago. You can find it at:  http://www.prismnet.com/~moki/20030126.073208/doubleXendXcapX.jpg .
The idea is to construct a very simple pressure hull out of two torispherical endcaps. The conning "tower" is made out of a standard line pipe with a little overdimensioned wallthickness and the smallest possible diameter. The endcaps are made with a small cilindrical section on it but i am afraid that the tower will intersect with the torispherical part.     
In order to keep it simple i chose a very common steel for the endcaps. It is P265GH (yield strenght 265 n/mm^2, 38500 psi, tensile strenght 410 n/mm^2, 59500 psi). This is an "off the shelf" material at Afflerbach, the german manufacturer. I think you could call it soft boiler steel.
To calculate the strenght of it (apart from the conningtower and viewports) one can use the formulas for a sphere, using the dishing radius of the endcap (in this case 1040 mm). Maybe it is my age, to much alcohol or lack of intelligence but watever method i use (ABS, Lloyd's or an old pressure vessel codebook) i get different outcommings. Can anyone of you say something sensible on this? I am considdering a wallthickness of 12 mm, divingdepth 100 mtr?  
If it is ever going to be build it will be tested unmanned to a depth 50% more than its safe working depth. Should it collapse i will hold no one responsible for that. So please be free to give your advise.       
 
Thank you very much,
 
Thijs Struijs