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ABS Rules for Building and Classing Underwater Vehicles, Section 3.3.1, requires a hydrostatic test "to a pressure equivalent to a depth of 1.25 times the design depth for two cycles." In a previous email I incorrectly stated that this test was against the maximum operational depth. Using the design depth makes much more sense. I think good policy is to consider the following...the calculations you will be using to design your sub are based upon equations that reflect perfect geometric shapes, or minimally, accepted tolerances pertaining to those shapes. They are, therefore, predictions of failure and do not represent exact failure points. The question you need to be concerned about is, how close to perfection are your fabrication skills? For example, if a 48 inch diameter hull is limited to an out-of-roundness of .125 inch but you discover that your hull is out-of-round by .365 inch, then you already have a weaker hull incapable of reaching the depth provided by the design calculations. Now add up all the potential areas of fabrication that potentially fall below the performance predicted by the equations and I think a home-builder would be silly to presume that they should operate at or near the design depth. The maximum operating depth you impose on your submersible is simply a matter of risk assessment for your own well being. I think it is wise for people to remember that even though a specific sub might pass 1.25 times the design depth for two cycles (as required for ABS certification), there is no guarantee that the sub will survive 3, 4, 5 or more cycles. The Seeker-100 accident (see web site) is a perfect example of this. In that case they dove two previous times successfully, to the same depth, with the same configuration, before the viewports failed on the third dive. I think a healthy safety margin is a good thing and so did George Kittredge who assigned a 2-2.5x safety margin on his vessels. Jon On 12/9/2010 6:31 PM, JimToddPsub@aol.com wrote:
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