There are lots of epoxy products on the market, and those that score highly with sailors tend to be reasonably priced, easy to use and effective. Pettit’s EZ-Tex is all three. It’s a two-part compound that mixes in a 1:1 ratio and bonds to just about any surface, above or below the waterline. I’ve used it to fill fastener holes in the deck, and it mixes easily and dries rock hard. It can be sanded, drilled, and painted. Available in 4- and 16oz kits, EZ-Tex is white in color. $19.99 (4oz), $39.99 (16oz).
Pettit Paint, pettitpaint.com