|
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,
-----Original Message----- 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. Rick Lucertini Vancouver, Canada |