<style> <!-- /* Font Definitions */ @font-face {font-family:"Cambria Math"; panose-1:2 4 5 3 5 4 6 3 2 4; mso-font-charset:1; mso-generic-font-family:roman; mso-font-format
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[FONT="]If you decide to use G10 fiberglass plate, I have found (after trashing bandsaw blades, expensive circular saw blades, and multiple jigsaw blades) that the best way to cut it is to use a diamond coated jigsaw blade. Then sand off the sharp corners and one side of it so the epoxy will stick. I have found the best way to sand G10 is to place a piece of sticky longboard sandpaper to a piece of scrap plywood and then run the G10 over this. G10 smells really bad when cut and I highly recommend a respirator if you have it, or at very least a dust mask. [/FONT]
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[FONT="]Good luck![/FONT]
Edit- If you decide to cut more, a Fein Multimaster type oscillating tool is what you want. Best tool in the barn for boatwork. Also, if you are really worried about the plywood you can remove it all, and replace it with a 1/2" thick G10 plate and then glass over the bottom of it. This will take more thickened epoxy but is quite manageable in this small area. If you go this route, expect to find some amount of soft or rotten balsa core around the plywood if the water has migrated that far. This may or may not be a problem. But I have found the more you dig the more you find, and then its up to your comfort level of how much you want to keep digging (and more importantly repairing)!
Second edit- Overhead fiberglass work is unbelievably messy. Plastic sheet everything within a 10 foot radius, wear a hat, and be very careful what you touch.