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Originally Posted by Penelope_Grey
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Originally Posted by jazman
Size has nothing to do with the pressure found at a depth. You put a Gato or a Type VII at 300 feet, they face the same pressure.
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Semi-True, however the Gato has a larger surface area, therefore the total area of pressure is greater than that of a U-Boat. as in.... Pressure per square inch is the same, but a Gato has a lot more inches than a U-Boat does. So will naturally not be able to go as deep due to being larger. |
Well, you're almost right.
Take a square inch of plate, set in a nice solid frame. The net pressure on that plate is outside pressure - inside pressure. At 350 feet, that's pretty high. Say that the plate is strong enough--for whatever reason (thickness, material, bracing). And the forces on that plate, if you do a Free Body Diagram, are evenly distributed on the outside, with an equal but opposite force spread around the edges of that plate (because it's sitting in a frame). You can intuit that the middle is going to dimple / collapse first--there are some strange forces applied in there to the material.
Say the pressure is 300 psi. On that plate, you have three hundred pounds. Around the edge of that plate, the 300 pounds are over 4 inches of the mounting frame, so it's 75 pounds/inch.
So, you make that plate a piece 9 inches square (3 x 3). The total force on the outside is now 2700 pounds, and the frame has 12 inches, so it's 225 pounds /inch. Hmm, that's a lot higher. The forces working on the material in the plate are higher throught (just do a FBD on an infinitesimally small edge piece), it will, if you slowly increase the pressure, collapse before the small plate.
But suppose you build a grid frame to hold that larger plate, where it's basically a 3x3 frame to match.
Then it's all the same. It comes down to what you design it to do. The total German design--thickness, bracing, etc., was designed to operate at a deeper depth. The bracing gets a little easier if you keep the ship smaller. More bracing: Money and Construction Time, and increased complexity (with increased possibility of poor build quality), etc etc etc.
But what you get is a smaller ship, and we Yanks need our Ice Cream machines.
BTW, a long long time ago, in a Galaxy far away, I was offered a job at Electric Boat. I turned it down for warmer pastures.