Rutgerson 370x164 mm portlight gasket/sealant question

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Hello,

I removed the starboard cabin portlight on my Bav 47 because the polycarbonate sheet was loose in its frame (eg = leaking). That is an easy fix. However I'm curious over what I discovered on the stainless sealing surface of the window (image attached). There seem to be three sealants on the cabin-window frame interface: a black sealant on the outer rim, a PU foam(!) lining and finally some white sealant. However when looking at Rutgerson official mounting instructions all I can see is some good'ol Sikaflex  applied to the bare stainless frame, no PU foam.

Does anybody know about this foam piece? Is it for ... trapping condensation or something? To catch condensation drops from falling in between the interior ply and the foam core? Simply a botched up job by a previous owner? My present plan is to simply remove all gasket remnants and simply go with a white Sikaflex per official instruction. Thanks!

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Followup #1

I'm going to ignore the old foam and black-white Sikaflex mix in the old window seal and try to go with a Butyl tape seal instead.

This is going to be somewhat tricky, as the surfaces do not really form a lap joint, as the stainless steel frame of the window is concave relative to the side of the boat - in short the joint is between a 1 mm stainless steel edge and the GRP plastic. A lap joint is preferred, as the sealing surface is larger. Presently in my view the stainless edge of the frame acts as a knife to whatever is put into the joint. So in this regard Sikaflex might even be a superior choice to fill the concave gap (see primitive drawing attached).

After completely cleaning the window frames (except for a moulded rubber sealing lip on the steel frame) I'm quite frankly appalled by the poor workmanship on this Rudgerson window. The window panel is so poorly cut that at points the joint between the moulded rubber lip and the panel is barely 1 mm. It looks like a 5 year old cut it out with a jigsaw. Terrible, just terrible. CNC machines excisted in 2001, that I know.

Secondly, the outside frame and inside bracket screw holes are seriously misaligned - obviously from the factory. The window fixing screws screw into stud-welded nuts, which are obviously broken on both my cabin portlights. The misalignment is 50% or more, eg. circles that should be concentric only meet 50%. I ended up re-welding one of the studs which was heavily misaligned and consequently broken off at its foot. Again, really terrible quality. My starboard portlight has been hacked too (bolts drilled all the way through) to obviously try and repair this misalign.

I have decide to replace the botched up old window panel and managed to purchase a leftover piece of UV-protected 8 mm polycarbonate sheet (which boat windows are made of usually). To confirm: the Rutgerson window panel thickess is 8 mm. I'm opting for a clear finish glass instead of the old tanned one to get more light into the otherwise dark cabin.

Images attached below. I'll post once I finish the repair.