Fixed port windows rebuild

I am fighting with fixed windows for 2 years with them with different levels of success, but loosing for now.

Original state:

Originally, they were set fiberglass resin (likely gelcoat) to the cabin top substrate. With zero elasticity and as result original plex just cracked due to thermal expansion/contraction. When I got this boat windows were cracked and leaked over cracks and around the perimeter.

Attempt#1

I do not know who and why designed this way, but port window frame gives about 10mm (<1/2 inch) area to bond lens, as well surface to mount slightly curved, means provide constant force to pull front and back ends of lens out of the frame.

I made new 1/4" acrylic lenses to size. Installed using well-advertised Sika 295UV with activator (actually sealant was more expensive than lenses). Followed all manufacture recommendations with cleaning e.t.c

Attempt#2

In about half a year one port started drip leaking. inspection showed Sika de-laminated from Plexiglass. I suspected I messed with surface prep or did not apply window in skinning time or so.

I cleaned all sealant and also scuffed plexiglass in the area of contact. Re-did the installation for both sides with the Sika again.

Attempt#3

This time it survived for a year and start dripping. Inspection showed the same failure mode - de-lamination from plexiglass.

My theory here was the UV light is going through glass and disintegrate bond layer between Sika ind plex. So, I changed my strategy.

Next ATTEMPT was also very well advertised in groups way with VHB tape and 3M 4000UV. The idea is very promising, however due to the very small border around did not survive a half year. I did not inspect what and how failed, but I suspect the small contact area did play role here as well.

Attempt#4

I tired to fight with adhesive mounting and decided to change strategy. Actually male tripple waranty on new design.

a) Make port windows mounted with fasteners to avoid pulling load on sealant. Yes it will be screw each 70mm of the frame - 36 screws per window. I know it is a lot of holes, but I hope it will keep this lens on place without stress on connection.

b) Plan to use other sealant on the window lip - DOW 795, it is good for skyscrapers, and must be good for us. DOW stating good compatibility with acrylic (plexiglass) and Lexan. Many people in network recommend it, so, why not to try

c) Put butyl tape on outside perimeter.

New construction:

Window flange will look like this: