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Hi, David and Bill - please remember that the
air/water pressure we are discussing is no more than a column of molecules being
sucked down by gravity.
That 14.7 lb. per square inch is the WEIGHT of
a column of air that is the height of the atmosphere, nothing more. The
same weight is achieved in sea water at a mere 32 feet, hence the term
"one-at".
Regarding hull pressure testing, the easiest way to
do this [and low, low, low budget] is to drag it into deep water and sink it on
a chain.
There are three test depths to monitor: [1]
operational (i.e.: over and over without damage) [2] test depth (say 1.5
to 2 times operational depth (eventually will sustain damage) and [3]
crush depth - self-explanatory.
Keep records, have the hull checked out
professionally. I would feel weird doing it, and wouldn't promote
this practise, but, if you have a confirmed crush depth of 900 feet, it's
probably safe to say that your hull's operational depth established arbitrarily
at 100 feet is an appropriate guess. That's a 9 to 1 safety margin - not
bad.
If you've dunked the thing to 300 feet, 20 times,
and nothing happened, then, again, operational of 100 feet would PROBABLY be
fine.
Caveat: engineering a pressure hull is a well
established science. Bring your drawings in to a pro, follow the drawings
when building it.
Rick Lucertini
Vancouver
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