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RE: [PSUBS-MAILIST] Design depth

Hey, there is a lake  that is 60 feet deep in Kansas Jon. hahaha
 
-Scott Waters
Date: Sat, 11 Dec 2010 13:57:12 -0500
From: jonw@psubs.org
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Design depth

Alan,

The definition for rated depth doesn't include any wording for a 1.25x safety margin.  It is nothing more than the depth to which the vessel has been operationally tested.  Absent a test chamber, the only way for a home-builder to "rate" their sub is to test dive it to some depth.  However, that depth may be significantly less than either the failure depth or predicted maximum operating depth.  For illustration, imagine the owner of a K350 who lives in Kansas where the deepest lake is no more than 50 feet.  If they go to 30 feet the first time they dive their sub, then that sub is only rated to 30 feet even though it is a K350.  If they go to 50 feet the second time they dive the sub, then that sub is now rated for 50 feet.  Assuming they never travel out of Kansas that sub will never be rated for more than 50 feet.  It doesn't mean the sub can't go to 350 feet, it only means it hasn't.  In this specific example I don't think adding a safety margin (1.25x) makes sense, and by definition its not required.  See ABS Underwater Vehicles Section 3.5 for a good example of how rated depth is used.  As I understand the ABS rules, rated depth is equivalent to saying "What's the maximum depth this sub has been operated at?".

Associating design depth with operating depth (maximum or not) doesn't make sense to me, but I guess I'll have to live with it.  We then need to include "failure depth" as a definition to our guidelines.

Jon


On 12/11/2010 12:30 PM, Alan James wrote:
Jon.
A bit of nit picking here but it seems the "rated depth" is the test depth devided by 1.25 (for ABS).
Or the same as your maximum operating depth.(design depth) & "Not" the deepest depth the vessel has been tested to.
 
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." 
ABS defines Rated Depth as:
 
"The depth in meters or feet of water (seawater or fresh water) equivalent to the pressure for which the underwater unit has been operationally tested in the presence of the Surveyor, measured to the lowest part of the unit. The rated depth may not exceed the design depth."  Note the last sentence.
 ABS defines Design Depth as:
 
"The depth in meters (feet) of water (seawater or fresh water) equivalent to the maximum pressure for which the underwater unit is designed and approved to operate, measured to the lowest part of the unit."