The aluminum frames are a custom commission from Bristol Yachts as far as I can tell and are unavailable for replacement. The frames tend to suffer from stripped threads in the screw holes. The original machine screws were aluminum and may be corroded. They are very easy to strip, either the threads of the screws or the tapped holes in the outer frames. If the screws were replaced with stainless steel screws there is a higher chance of corrosion which will weaken the threads in the tapped holes.
The screws will not all be the same length, so when you remove them mark which hole each screw came out of.
Once the frames are removed you will find the rough cut opening consisting of the outer skin of the cabin side, a gap of about a 1/4" and the inner skin of the cabin liner. As the frame is screwed together, it squeezes the two skins together. Not a good arrangement especially when the tapped holes will strip out as soon as you look at them. A stronger solution would be to fill the gap with thickened epoxy prior to reinstalling the frames.
To replace the lights in the frames,
- Remove the frames and mark all the pieces.
- Clean them of all the old mastic or other caulking that has been added over the years. They need to be completely clean. I soaked mine in paint thinner for a few days, then scraped them clean. Don’t remove the anodizing by sanding or wire brushing.
- Acquire new 1/4" thick lights. I used slightly tinted polycarbonate—very very very strong but polycarbonate suffers from UV damage. Since the frames are the weakest part of the ports, it probably is over kill to use Lexan.
- Cut the new lights to the inside boss shape of the outer frames. You can cut them on a band saw or jig saw, and a belt sander is useful to clean up the edges. Use the old plastic lights as a template.
- Glue the light to the inside lip of the outer frames with clear silicone sealant. Use some weight to hold the light in place until the sealant kicks. Wait a day to install.
- Caulk the outer lip of the exterior frame with your favorite non-silicone caulk. I would not use anything that is an adhesive—such as 3M 5200 or 4200. You will only damage the frames when you need to remove them in the future.
- Position the outer frame with the light installed in position and use some painters tape to hold it in position. Alternately, have someone available to hold the outer frame in position, if posssible.
- Position the inner frame against the opening and run the screws into the tapped holes loosely and carefully. Do not caulk the interior frame—it is a waste of caulk and will not seal the window.
- Cross tighten the screws (very gently) as you would tighten the lugs on a car wheel so the intertior frame is not warped out of alignment.
- Clean off the excess caulk around the exterior frame.