I assume you are sanding the edges of a piece of fiberglass, not the gelcoat finished surface. Once you get an angle grinder, you'll never go back. The little Dremel sanding discs are too small for any real work, and if your electric drill is any good, the glass in the fiberglass will act like sand in the electric motor and prematurely wear it out. BTW it'll do the same thing to your lungs as well, so if you have a shop vac or any vac with a filter bag, set it up right next to your grinding table. Go to the paint dept. and get special dust masks for drywall/fiberglass. Wear gloves and put baby powder on your arms before starting. Rinse hands/arms in cold water after you're finished. Unless you enjoy endless itching. Junky Chinese angle grinders are 5 bucks and you can use the grinding wheel that comes with it on 'glass. A deeluxe kit will also have a sanding disk backing plate. You'll maybe find more uses for the angle grinder than for your drill, like sharpening stuff, cutting off padlocks when you lost the key, cutting hard plastic as well as metal shaping.