Jon,
ABS requires a pressure test to 1.25 x the design
depth.
The rated depth may not exceed the design depth. So it can't be the test
depth.
I read this as follows.......
For certification purposes you have your sub tested to 1.25 x your maximum
operating depth,
wich should be half your crush depth. Having passed the test they certify
you & say you are now
rated for your maximum design depth.
If you had a crush depth of 1000ft & tested to 999ft would you say that
your sub was rated for 999ft?
I am reading rated as meaning "rated for safe operation to"
Regards Alan
----- Original Message -----
Sent: Sunday, December 12, 2010 7:57
AM
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."