I used Pettit EZ Tex Marine Epoxy Repair Compound to fill screw holes in the transom of a boat to which a new transducer was being installed. I needed a tough, watertight fix.
My methodology for effecting such a repair includes drilling the existing hole out to four times the diameter needed. After the epoxy cures, I drill for the new fastener and reinstall whatever it is that needs fastening. In this case, I drilled out the two No. 10 screw holes using a half-inch bit and filled them using Pettit EZ Tex. EZ Tex is a two-part product that is easy to mix because it blends at a 1-to-1 ratio of epoxy to hardener. Other products mix at 3-to-1 or 5-to-1, and so are tough to mix accurately by the eyeball method in the field and may fail as a result.
EZ Tex also cures without shrinking, meaning I only had to fill the holes once and scrape off the excess before cure, as opposed to multiple fillings and time spent flattening an overfilled repair prior to refastening. EZ Tex is white and paintable, and can be used with fiberglass, metal or wood. It cures in 24 hours at 50 degrees and is said to cure in five hours at 70 degrees and 3.5 hours at 90 degrees.
The owner reports no leaks from the transducer that he and I installed. $26.99 (4 ounces); westmarine.com