[Tommy]

I can't describe it better than the many videos online. Essentially I grind away some of the original fiberglass so there is a tapered area around the holes for the new fiberglass to go. Lay in layers of fiberglass mat (with hairy looking random fibers) wetted with the appropriate resin. I build it up higher than the finished surface and completely cover the hole. When it has set, I cut the new hole and grind it down to the right height. When that is done I top it with gelcoat before painting (and gelcoat is a whole lesson in itself). ... Watch a few videos for more details.