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Hi Frank,
I think Stachiw would say 1/8 is too
much. Part of the window strength comes from the thru-hull fitting.
If you don't have the Handbook of Acrylic book, I truly recommend you purchase
one, or borrow one from your local library. There's good detailed
information in it regarding thru-hull fittings for the window, both text and
illustrations.
CAUTION: PREACHING ZONE FOLLOWS....NOT
INTENDED TO OFFEND...
Viewports are an integral part of your
pressure vessel and as important as any full penetration weld. Don't risk
your life, or worse, don't risk the life of a potential passenger by guessing
about viewport and fitting design. If you've already spent $10k, $15k,
$20k or more on parts and materials, go ahead and spend another $200 on the
Handbook of Acrylic by Stachiw. It's only a 2% (or less) increase in the
total cost of your submersible. Here's a link to a lesson on what can
happen when windows are not designed properly http://www.psubs.org/accidents/seaker100-1.html
Jon
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