Jim,
Design depth is derived from the parameters (material type, hull
thickness, number of ribs, spacing of ribs, etc) used in ABS/ASME
formulas to determine the maximum external pressure that the
submarine can operate in. I don't think ABS or anyone else can
reliably calculate "fail depth" or "crush depth" because those
depths are highly dependent upon quality of material, fabrication,
vessel use/maintenance, etc. The crush depth could be some
percentage above or below design depth, however you could only find
out definitively by testing the vessel to destruction. For that
reason, you don't want to perform a manned dive to 375 feet. Make
sure that is an unmanned test. You'll note that ABS Underwater
Vessels Section 3.5 limits the manned test dive to the design depth.
Jon
On 12/10/2010 9:04 AM, JimToddPsub@aol.com wrote:
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.
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