The key to a good gelcoat repair is color match. Try and get some gelcoat from a dealer who sells your brand of boat. If you can't, try spectrumcolor.com. They sell gelcoat repair kits that match a wide variety of boats. Do not use the liquid gelcoat that is normally sprayed on. You must use a paste. If you get the geocoat from your dealer, it will most likely be in the sprayable consistency. Buy some cabosil and make it into a paste. Prep the spot by chipping any loose gelcoat with the corner of a razor blade, then sand it the area with #300 sand paper. Clean the area well with acetone. Use blue masking tape and tape around the area. mix the gelcoat paste with a drop or two of catalyst and mix well. Spackle it into the area with a plastic putty knife, trying to get it as smooth as possible. Cover the repair with wax paper or plastic. Gelcoat won't totally cure unless you cover it or add wax to the mix. Let it cure for a couple of hours. I usually just come back the next day. Then, starting with the #300 wet/dry sand paper, sand the area, blending it to the surrounding gelcoat. Continue sanding with finer paper to #1000, then use rubbing compound and then polishing compound. Hopefully by now you will see some shine and then you can polish and wax. Sounds like a lot of work, but once you get the process down, it goes pretty fast.