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Jim gave the ABS definitions of design and rated depth which match the descriptions I gave from the PSUBS guidelines. Operational depth is purely arbitrary except that it cannot exceed the design depth. I think the confusion comes from how you approach the design phase, and there are at least two ways to look at it. The ABS/ASME way of viewing pressure vessel design is to pick a maximum design pressure (which the operating pressure would equal) and then add material to deal with corrosion issues and safety margin. Remember, ABS/ASME rules are for pressure vessels, not specifically submarines. In other words, a 1ATM submarine is always a pressure vessel, but a pressure vessel is not always a submarine. This approach validates the 1.25 overpressure test since they are essentially saying, pick your design/operating pressure and then increase it by .25x to pass our test requirements. Using this method, if Jim wants a submarine capable of 600 feet he actually has to calculate and fabricate the submarine to survive 750 feet. A different approach is to say, I know I don't want to dive deeper than 300 feet (my max operating depth) and I want a 2x safety margin. That means using material capable of withstanding 600 feet depth. Now with this approach you certainly may not pass a 1.25 overpressure test for a 600 foot design depth, however you've already self imposed a 2x safety margin. If you wanted ABS certification, then you simply claim the design depth as 480 feet. Now you meet the ABS requirement (480 x 1.25 = 600) and also are still well within your 300 foot self-imposed depth limit. In my opinion the 1.25x safety margin is not a comfortable margin, but for consistency if PSUBS is going to recommend a mininum safety margin then we should recommend the same as ABS. Jon On 12/10/2010 12:23 AM, Alan James wrote:
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