samfieldhouse
Well-Known Member
We know the score; 80s boat with perspex windows down the side of the coachroof - I'm after a sense check on my plan...
Firstly, there is, as always, great info on this site so if you've come here through a Google search read these articles too:
Hadlow marine have some excellent instructions on how to fit windows using Scapa tape.
Current Status
Windows out (8mm). They were previously secured with self tappers and some otherworldly adhesive. Which made the self tappers pointless. Maybe the adhesive was Sikaflex but by golly. It was 2mm thick and 40mm wide all the way around. Pulled the gelcoat off in places. Also broke the windows if I pulled too eagerly.
I ended up using a mallet to drive a scraper between the cabin and the window, and then inserting a bread knife to saw through the adhesive.
Amusingly, despite all that adhesive, they still leaked!
My plan
As the self tappers have penetrated the cabin anyway I've opened out all the holes to 5mm. I've also countersunk the holes to prevent further gelcoat damage at the edge.
I like the idea of using Scapa tape. I'll stick it to the GRP and when the nuts tighten up, it forms a watertight seal under compression. Plus no mess and easy future removal. A good idea?
I'll bolt thought with M4 machine screws, with wide flange heads like these from the nice people at Westfield (highly commended). In the 5mm holes that will leave wiggle room for differential expansion - will they? Which should prevent cracking.
I'll secure internally with either nuts with a captive washer or oversize washers and dome nuts. Thoughts on this?
On the Scapa Tape - it requires a minimum 30% compression to make a seal.
I can get 4.5mm which would need to be compressed to 3.1 or 3mm to 2mm. I'm thinking the 4.5?
So in essence - new windows will be 8mm thick, with 5mm holes for fixings, secured by M4 machine screws, sealed with Scapa tape.
Sound sensible?
Firstly, there is, as always, great info on this site so if you've come here through a Google search read these articles too:
Hadlow marine have some excellent instructions on how to fit windows using Scapa tape.
Current Status
Windows out (8mm). They were previously secured with self tappers and some otherworldly adhesive. Which made the self tappers pointless. Maybe the adhesive was Sikaflex but by golly. It was 2mm thick and 40mm wide all the way around. Pulled the gelcoat off in places. Also broke the windows if I pulled too eagerly.
I ended up using a mallet to drive a scraper between the cabin and the window, and then inserting a bread knife to saw through the adhesive.Amusingly, despite all that adhesive, they still leaked!
My plan
As the self tappers have penetrated the cabin anyway I've opened out all the holes to 5mm. I've also countersunk the holes to prevent further gelcoat damage at the edge.
I like the idea of using Scapa tape. I'll stick it to the GRP and when the nuts tighten up, it forms a watertight seal under compression. Plus no mess and easy future removal. A good idea?
I'll bolt thought with M4 machine screws, with wide flange heads like these from the nice people at Westfield (highly commended). In the 5mm holes that will leave wiggle room for differential expansion - will they? Which should prevent cracking.
I'll secure internally with either nuts with a captive washer or oversize washers and dome nuts. Thoughts on this?
On the Scapa Tape - it requires a minimum 30% compression to make a seal.
I can get 4.5mm which would need to be compressed to 3.1 or 3mm to 2mm. I'm thinking the 4.5?
So in essence - new windows will be 8mm thick, with 5mm holes for fixings, secured by M4 machine screws, sealed with Scapa tape.
Sound sensible?
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