I worked in a boat repair facility for 4 years doing this type of repair. My best advise is, if possible, take the boat to a professional fiberglass repair facility that does boats. I saw too many self done butcher jobs. Glass work is not hard, but the more you do, the better you get. Tackling soft hulls on your hobie as a first time job, and then gel coating...egads, save some grief and be kind to your boat. Get someone else to do it.
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<br>If you can't get anybody else, then drill very small holes about 3-5 cm apart. Inject a 30 minute epoxy with no thickening agent and come back and fill the holes with epoxy after a couple of hours. If you try and gelcoat, mix a small amount with colored dye in it and use some wax paper over the repair to minimize sanding. This stuff is hard as a rock and in trying to sand it you'll muck up the rest of the finish on the boat.
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<br>Just my 2 cents.
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<br>Cheers!<br><br>