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Jon,
I need to read and study the whole ABS publication
thoroughly, but from what I've read is seems that the Design Depth I would need
to claim would be 300 feet. During the survey I would need to dive in
increments to 375 feet (300 x 1.25). The vessel would then be rated to 300
feet. Per ABS, Design Depth is the depth to which the vessel is "designed
and approved to operate." It's going to be approved to 300. If I
want to have it approved for anything more than that, I'll have to have it
surveyed to 125% of whatever I want its operating depth to be.
What is surprising is that [so far] I see nothing in ABS that
specifies how the Design Depth must be derived. It seems rather arbitrary
rather than stating something such as "60% of the calculated fail
depth."
Jim
In a message dated 12/10/2010 1:24:29 A.M. Central Standard Time,
jonw@psubs.org writes:
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. |