----- Original Message -----
Sent: Monday, February 21, 2005 1:01 PM
Subject: RE:
[PSUBS-MAILIST] acrylic viewport thickness
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.