RE: [PSUBS-MAILIST] Pressure hull

["Alec Smyth" <Asmyth@changepoint.com>]

Thijs,

 

I love the simplicity of a hull made from simply two endcaps. I thought mine would be simple enough as it is basically a reinforced pipe, yet welding two elliptical heads like this would have saved me at least 6 months work, or more. The reason is you would not have to contend with a cylinder which is never quite round when you receive it, and getting round rings into an oval cylinder was the hardest thing on the whole project so far. The part I would worry about is that you have inserts that cross the join between the two halves. Not that it can't be done, but it introduces what to me at any rate are unknowns in the stress calculations. I try to use only things that I can calculate.

 

Besides Cousteau's saucer, there is another sub out there based on this principle of joining two elliptical heads. Unfortunately I can't recall its name, but I remember seeing a picture of it online somewhere, hanging from a crane and painted white and orange. If anyone can recall the sub I'm referring to, you might find it a neat idea. What they did was incline the "saucer". It was oriented in a horizontal plane like Cousteau's, except it was also inclined "up hill" about 30-45 degrees. While this might seem odd, they also had an exostructure that faired it. The lower head had two bubble windows facing forward, but as the saucer was inclined, these two windows did not have to cross the weld between the two heads. The occupants traveled lying down and the hatch was of course on the upper shell.

 

rgds,

 

Alec

 

 

 -----Original Message-----
From: Thijs Struijs [mailto:thijs-struijs@planet.nl]
Sent: Sunday, February 09, 2003 12:02 PM
To: PSUBS
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