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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."
Alan
----- Original Message -----
Sent: Sunday, December 12, 2010 5:20
AM
Subject: Re: [PSUBS-MAILIST] Design
depth
I don't think that definition fits, Vance. A divers
operating depth one day could be 30 feet and 300 feet the next day.
Neither of those data points is effective in communicating the maximum safe
operating depth of the sub. Likewise, Phil used "working depth" in his
reply, but working depth is just as generic as operating depth. To me,
your working depth is what ever depth you happened to be working at in a
particular moment of time.
"Hey, I dove in a DW2000 today"
"No
kidding. What was your working depth?"
"Oh I was just checking out
some underwater pipes at 100 feet"
That seems like a very logical
conversation that could take place after a dive, yet it in no way communicates
the operating limit of 2000 feet that the vessel could have been taken
to. In the home-builder arena the term use becomes significant because
there are likely instances when even "rated depth" could be used in the wrong
context.
I think there are three data points that home-builders need to
be aware of. The first is crush depth, failure depth, design collapse or
whatever other term you want to call it. It is, however, the theoretical
failure point for the vessel determined either by calculation or FEA, which I
believe ABS appropriately termed "design depth". The ABS definition is
faulty however because they mix the words "designed and approved to operate"
which introduces confusion by interpretation. Other references to design
depth by ABS in their rules document make it more clear that they mean failure
depth. Perhaps "Failure Depth" is the term we should use here since it
should not cause the same confusion as does design depth.
The second
data point is either safety margin or MAX operating depth.
The third
data point is the "rated depth" which is the deepest depth the vessel has been
tested to.
With these three data points the home-builder and PSUBS
enthusiast has all the performance data they need to make reasonable
interpretations about the safe diving parameters of a particular vessel.
The failure depth is the most important data point however since everything
else is a factor of that depth.
Jon
On 12/10/2010 2:25 PM,
vbra676539@aol.com wrote:
You guys have fallen head over heels in love with a logic
trap, heavily basted with semantics. Give it up. Design depth is your
operating depth PLUS the percentage required for testing. It means the depth
to which the pressure vessel may be taken repeatedly without incurring
irrecoverable damage.
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