This theme is quite tricky – all submarine viewports are made of thick cast acrylic – the resin is curing in a process that creates a LOT of heat so forms for thick walled acrylics are surrounded by a water bath to deal with that heat. The process also tends to create bubbles within the material – so the whole casting process is done in a pressure chamber. Even so bubbles appear on the contact area between form and resin – the manufactureres solv e this problem by making the piece bigger and machining it down a couple of milimeters to get rid of the bubble zone and produce a perfect transparent viewport. After that the viewport has to be heat treated to reduce tension build up – it will shrink in this process up to 10%. It also needs to be polished for hours to get a transparent surface.
All this explains the tremendous cost of thick acrylic pieces in high optical quality. To get good results is almost an art form.
building viewports from other plastics (epoxy, lexan) has been discussed but did not get implemented as far as i know.
The tradition to do it in acrylics goes back to piccard and trieste – this sub reached the mariana trench 11.000 m with acrylic viewports (cone shape).
Busby, who is kind of moses in submarine design said that acrylic is the indicated material because it will give you a warning sign in form of a crack BEFORE it fails definitly – so you can end the dive with a cracked viewport and still walk out alive.
Then came stachiw with his 1000 page plus book about acrylic viewports in submarines and since then all has been acrylic.
So shred if you try it in other plastics you are basicly on “new territory”.
A dome viewport in the 6 foot diameter area can easyly cost 50k if you buy it as classified submarine viewport. A acrylic piece of the same shape and appearance purchased from a decorative item shop can cost only 500 USD.
What ever you decide to do in submarine windows keep in mind that testing it at a load 3 times the load you plan to use it would be a prudent approach.
Also keep in mind that plastics are suceptible to cyclic fatique dome viewports on tourist submarines are changed after 10.000 dives due to fatique reasons (recommended by stachiw – and took over by most regulatory norms about pressure vessel viewports)
I’m rather sure that most resins would crack before failing…
So I ended up making 2 different lenses, one with oil and one without, the one with oil, took a long time to dry, and ended up falling apart rather easily, the one without turned out rather well, even though a little clay got stuck to it, can likely file it off.