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Re: [PSUBS-MAILIST] FEA of a Basic Flat Acrylic Viewport



Hi Alec. I would guess that removing and re-using a lens sealed in urethane would be difficult, if not impossible. The Sikaflex 295 is what I was considering too. Now, for maintenance, if the lens is sealed in, is it necessary to remove it ? What maintenance task is necessary that would require removing a lens other than replacing a lens because it was damaged or reached it's maximum life cycles ? If a dome or disc is damaged, well, then you won't be using it again anyway. I'm trying to imagine a scenario where I'd need to pull one out and re-use it. Coming up with nothing. Repainting wouldn't need a removal unless there was rust or corrosion in the pocket. Pulling the lens to put something through the hole ? The hatch would be the logical choice for that.
How often the lens needs replacement would depend on how many cycles it's been through, and how well it's protected from UV and scratches. Although a lens is a considerable investment, it's relatively small compared to the overall cost of the sub, and after all, the windows are the main reason for building a sub in the first place.
My main window is going to be exposed to wave action when surface traveling. I hope to be able to motor along relatively quickly with the ''outboard'' option. To prevent collision with small floating debris while running on the surface, I was thinking of a removable cover for the main window. I saved the disc I cut out of the hull for the main window so I could use it as a cover. Haven't really spent much time on the design, but thought I could just add an angle iron ring with latches  that can be released easily to the cover disc, and then put the cover in the support boat when readying for a dive. It could possibly be attached to the hull for storage while diving too, as long as it was in a location that didn't get hung up on something.
I had some discussions earlier here about a bow shaped plexi cover that would stay in place, but bubbles get on the inside and would interfere with the view. A removable cover seemed like the next best option. 
Anyway, Have you had to replace any of your plexi besides the instance where the seal was bad?
Frank D.




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