Rick,
I?d really recommend
you get yourself a copy of the PVHO. It?s a little pricey, but one of the most
valuable texts out there in terms of the usefulness of the information. What
you?ll find is formulas and guidelines of a very practical nature for
calculating just this sort of problem.
There are two basic
fabrication techniques for domes; you can cast them in a mold, or blow them
with compressed air. Casting is the method on all the certified subs you
mentioned, but a cast dome costs tens or even hundreds of thousands of
dollars. For PSUBS, you?re probably looking at blown domes. A sheet of acrylic
is fastened by a ring to a flat surface. The assembly is heated, and
compressed air injected to form the dome. There?s more to it than that, but
that?s the basic approach.
One of the challenges
of blown domes is that the material has to stretch out, and can get quite thin
at the apex. It?s the minimum thickness that counts when it comes to the
stress formulae. So a trick you might want to use is to blow a dome of fewer
than 180 degrees. In my case, I went with 120 degrees. It still looks and
feels almost like 180, but there?s a very considerable advantage in thickness
and hence strength. My window is made of 2? material, and at the apex it is
1.73? thick.
Cheers,
Alec
-----Original
Message-----
From: Rick and
Marcia [mailto:empiricus@telus.net]
Sent: Monday, February 21, 2005 3:33
PM
To:
personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] acrylic
viewport thickness
Hi, All - regarding the acrylic
viewports . . . does anyone know how thick the viewports are/were on the dome
type of subs like Hikino, Deep Flyer, PC-8, Deep Rover, etc. (Makakai
was constructed of sectional pieces glued together - beyond my
skills)
I'm interested in a 6ft.
diameter hemisphere to be used to 3 atm's (30 metres) max operating
depth. One-atm cockpit.
I originally considered using the
half-dome for an ambient-dry boat but, since 3 atm's is so shallow, I may be
able to afford a one-atm viewport. I have family that I don't want to
subject to barotrauma. They're all pre-teen and still
growing.
Separate issue: Anyone with a
knowledge of metal may be able to suggest framework for this half-dome.
I'm considering using 3 inch square tubing. Underkill?
Overkill?
If it comes down to it, I'll just
order a one inch (at the apex) half-dome and use the boat
ambiently.