I had typical beach dragging type damage to my boat from years of beach trips before Cat-Trax. I used a product recomended to me by car mechanic he had used on a corvette. It was a fiberglass resin GEL. The thicker product helped to build up the edge and repair the hull profile. It wasn't pretty, but serve the purpose until I sold the boat. Good prep makes the repair.
I sanded the repair area with a fairly couase grit automotive type sandpaper, to make a good maiing surface and get is clean. I layed on a couple of layers of cloth more out of precaution than anything and then rebuilt the hull shape using the thicker gel. It took tons of sanding and I ended up using an "Air File" (pnuematic inline sander) to work down the high areas. Agin this was not a pretty or professional job, but I was back sailing in a week with lots less water in the hulls.