Fixing polycarbonate coach-house windows

[Plank]

I have a Young 88 (Kiwi design) with ply coach-house. Polycarbonate windows are fixed externally by self-tappers screwed through the plastic into the timber. Currently have 3/4" 6g screws. There is a well formed Sikaflex gasket. Last season we removed all the screws and reinstalled with bamboo skewer plugs to add grip. Trouble seems to be that the screws still do not have enough holding power, the pressure on the gasket releases and leaks develop.
I can increase the length of the screws to 1" x 6g with little difficulty. Question is do I set the screws in Araldite to increase the grip, or maybe a high bond silicon sealant? I know the ultimate answer may be to replace all screws with bolts but it is ugly and I do not want to do it if I do not have to.
Any thoughts?
Plank (Sydney, Australia) <span style="color:blue"> </span> <span style="color:blue"> </span>

 

[ianabc]

The Wood Epoxy aturation Technique WEST from the book by the Geougon brothers in the USA suggest that epoxy filled holes tapped or embeddd with the bolts have a holding power equal to or above the holding power of the wood or of a wood plug.

OR perhaps bolts capped with tidy large washers on the inside?

An outside ring on top of the polycarbonate adds strength.

 

[Plank]

Good thought but drilling out and epoxy filling 64 holes on each side followed by tapping and bolting would be quite a job.
The boat is constructed using west System epoxy on cold moulded maple!
I am leaning to using the 1" screws and a good silicon on the threads.
Cheers

 

[Robin2]

I used nice looking bolts - pan pozi heads. I also managed to get some self tappers that look almost identical for places where I could not use bolts. On the inside of my boat the window bolts are hidden behind panels.

 

[srp]

You could use interscrews - this is a UK supplier so could be tricky for you. I know they are used for aluminium framed windows, but don't see any reason for them not to work with your setup.

 

[swampthing]

The screws dont even need to be there. Sikaflex bedding done correctly has a ferocious bond, but if it makes you happier, double the amount of screws and a coctail stick of epoxy in hole before screw. No need to overtighten.

 

[vyv_cox]

Make sure you use the correct grade of Sikaflex. Sika 291 can cause stress-corrosion cracking in polycarbonate. Check this page for advice. Sikaflex 295 UV is the correct one.