Jon, or any other enlightened person who is
awake.
Now I'm getting really confused, ( wich is not hard
to do)
You stated earlier.....
Design Depth = Maximum depth for which a vessel is
designed.
Rated Depth = The maximum depth successfully reached by the
vessel.
Operating Depth = Depth at which the vessel normally
operates
But below you quote ABS.....
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
I take it the design depth is not the crush depth or the hydrostatic
pressure test would crush it at 1.25 x.
So what is the definition of the design depth? Does ABS relate your
operational depth to your design depth
by some percentage figure?
Also after a bit more input maybe Psubs could come to some sort of
conclusion as to a recommended relationship
between "crush depth", "test depth" & "operating depth". (maybe a
vote)
Regards Alan
----- Original Message -----
Sent: Friday, December 10, 2010 5:10
PM
Subject: Re: [PSUBS-MAILIST] Design
depth
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." In a previous
email I incorrectly stated that this test was against the maximum operational
depth. Using the design depth makes much more sense.
I think good
policy is to consider the following...the calculations you will be using to
design your sub are based upon equations that reflect perfect geometric
shapes, or minimally, accepted tolerances pertaining to those shapes.
They are, therefore, predictions of failure and do not represent exact failure
points. The question you need to be concerned about is, how close to
perfection are your fabrication skills? For example, if a 48 inch
diameter hull is limited to an out-of-roundness of .125 inch but you discover
that your hull is out-of-round by .365 inch, then you already have a weaker
hull incapable of reaching the depth provided by the design
calculations. Now add up all the potential areas of fabrication that
potentially fall below the performance predicted by the equations and I think
a home-builder would be silly to presume that they should operate at or near
the design depth.
The maximum operating depth you impose on your
submersible is simply a matter of risk assessment for your own well
being. I think it is wise for people to remember that even though a
specific sub might pass 1.25 times the design depth for two cycles (as
required for ABS certification), there is no guarantee that the sub will
survive 3, 4, 5 or more cycles. The Seeker-100 accident (see web site)
is a perfect example of this. In that case they dove two previous times
successfully, to the same depth, with the same configuration, before the
viewports failed on the third dive.
I think a healthy safety margin is
a good thing and so did George Kittredge who assigned a 2-2.5x safety margin
on his vessels.
Jon
On 12/9/2010 6:31 PM, JimToddPsub@aol.com wrote:
Alan,
My design depth is 600 ft. Operating depth is 300
ft. Therefore required test depth would be 375 ft. Failure depth
must be slightly deeper than 600 ft.
What test depth would you consider to be best based on the
above? I would have thought 400 ft. which isn't much more than
the standard. We had an online discussion of this in early
October. I'll forward my last post which includes the comments of
others.