I laminated and made a 1/2 inch thick fiberglass board onto a sheet of glass that was waxed. I then drilled 6 inch round "donuts holes" with my hole saw and drill press. These donut holes are my solid glass backing plates. Yes it's more work but it's the right way to do it. Once I had my donut holes made I roughed the interior hull surface with a brass brush on my drill and also roughed the "rough side of my donut holes. I then mixed up a batch of fiberglass "kitty hair" and installed my backing plates. I used the small hole saw guide hole to put a threaded rod through so I could tighten everything down and I'd have a perfectly aligned and smooth as glass backing plate. Once the glass was cured I went outside and with my hole saw drilled my through hull hole.
Yes the screws go all the way through the hull but you counter sink them then apply 4200 or similar. Once that has cured for a day or two skim over the countersunk bronze bolts with West System and cabosil or 3M Blister Repair Putty. They don't leak if done correctly. On certain hulls like some Hunter's you may not have enough thickness to counter sink properly so in this case I would laminate more thickness on the inside of the hull so you can counter sink properly..
-Maine Sail / CS-36T
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Last edited by Maine Sail; 05-31-2007 at 06:42 PM.