I use Marine-Tex epoxy instead gel coat for surface repairs, But get A LOT of flack for not using polyester http://www.marinetex.com/marinetexepoxyputty.html
I've used it to build up the bottom of my hulls, repair both bows, the leading edge of my centerboards on my H17 (an annual thing) and several significant dings (Oh, the life of a river sailor) It works great, is easy to use, file and sand. You can paint, but not gelcoat over it. For major repairs I first do the glass work in polyester (fiberglass resin and cloth) then surface coat with the Marine-Tex. Since my boat is white, the white Marine-Tex is a good match.
Hint: If you have a H17 and want to build up the leading edge of your centerboard (the edge that gets dragged on the beach) prep the surface as instructed, apply a liberal amount of epoxy along the edge, then apply blue panter tape along both sides (no wrinkles) so the tape A-frames around the bead and tape-to-tape along the upper edge. Apply even pressure on both sides to squeeze out the air and even out the putty within the tape. If carefull you get a great leadind edge that needs just a little filing and sanding.