Chips, scrapes and gouges can be smoothed over with a little effort and the right product
The slimy walls of the canal lock dripped pale green drops on deck. Zebra mussels spit. My gardening gloves were covered in slippery black goop as I kept the mooring line strung fore and aft on Elizabeth, my 1976 Bristol 24, as tight as possible. The boat lifted with the rising water in the lock, one of 31 I'd negotiate between Troy and Oswego, New York, on my small-boat voyage up the Hudson River through the Erie and Oswego canals to Lake Ontario. While trying to fend off, I looped the bight of the mooring line over successive rungs of the ladder in front of me.
As hard as I tried to avoid it, the hull took a beating in the canals. Dings, gashes and gouges, some down to the laminate, required a major stint with epoxy, filler and the gelcoat repair kit when I finally reached Clayton, New York, in the Thousand Islands. Stress cracks in the corners of the cockpit, spider web emanations on the foredeck where I'd dropped the Danforth, and eggshells (sections where the gelcoat bulged out in brittle mounds) also needed attention.
Let's face it: A fiberglass boat isn't going to stay in pristine condition when you use it, even casually. Small sailboats take hits at the dock, on gravelly beaches, and at the launch ramp, in addition to the inevitable wear-and-tear accumulated over years of enjoyment on the water. The good news is wounded fiberglass can be repaired with a bit of know-how.
Most fiberglass boats, especially small ones, are made from polyester resin, largely because it's less expensive than vinylester and epoxy, which are much better materials for making boats since they're less prone to water intrusion. Epoxy and vinylester, commonly used as a barrier coat, are closed chain polymers. On the other hand, polyester is an open chain polymer. Essentially, what this means is on a molecular level vinylester and epoxy are "tighter" than polyester, and the "tightness" makes both types of resins less susceptible to absorbing water. Epoxy is an all-purpose resin that can be used for any fiberglass repair; polyester resin is best used only on polyester hulls and decks. You wouldn't want to repair an epoxy hull with a resin that's less resistant to water intrusion.
The repair process
The first step in the repair process requires cleaning and degreasing the damaged area. Any strong household cleaner such as Mr. Clean will do the trick. Rinse the area thoroughly and then apply a dewaxing agent (available at your marine chandlery) or simply rub the area with acetone. Dewaxing will remove wax residue and keep it from mixing with the resins used to make the repair.
Once the surface is completely clean, you have to make a judgment call about just how aggressive you want to get with the repair. I often simply sand a shallow ding or gouge to abrade the surface to help ensure a good bond, reactivate the old gelcoat by brushing on a thin application of styrene, and then use a gelcoat repair kit to fill in the void. When the mixture is cured, I sand as needed, wipe the area with acetone to remove any trace of the styrene, rinse thoroughly, and then apply a coat or two of good marine wax. There are all kinds of products on the market for simple cosmetic fixes and more extensive repairs, and choosing the one that best fits the job will make the repair easier.
With a deep ding or gouge, you'll have to grind the damaged area until the underlying laminate is exposed. This is the usual practice in boatyards. A Dremel tool works well, but any sharp, V-shaped edge will also work. Stress cracks and eggshells typically go all the way down to the laminate, anyway, so the more aggressive approach is often merited. Again, cleanliness is the order of the day. Use a stainless-steel wire brush to remove any loose pieces of fiberglass and wipe the area with a clean rag to remove dust.
If the damaged area is deep and wide, you'll need to add a filler of chopped fiberglass strand or fiber mixed in with the resin to fill the void before you apply a new layer of gelcoat. Trowel the mixture into the damaged area with a putty knife or a spreader (a Popsicle stick works well), making sure to tamp it down to remove air pockets that can cause voids, weakening the repair and allowing water ingress. Overfill slightly, let the filler cure for at least 24 hours, and then sand and wipe the area with a clean rag before applying a new layer of gelcoat.
When working with resins, it's important to choose a dry cool day with low humidity; an ambient temperature between 70 and 80 degrees Fahrenheit is best to allow ample working time (pot life) before the mixture begins to set. Temperature influences cure rates. The hotter it is outside, the faster the mixture will cure, and the opposite is the case in cold temperatures. A good working time to shoot for is about an hour. Make certain to follow the mixing ratios between the resin and the hardener as listed in the instructions, and make certain to mix the hardener evenly through all the resin. Avoid getting the mixture on your skin and try not to breathe the harmful vapors.
Mixing gelcoat to match the color of the area surrounding the repair takes patience. No matter how carefully you follow the instructions in the repair kit, the color won't be an exact match because the surrounding gelcoat will have oxidized with age. However, you can come pretty close if you slowly add the colors in tiny increments and compare the color of the mixture to the surrounding area in bright sunlight. Add and mix until you get as close a match as possible, then add the hardener just before you apply the gelcoat. Use a spreader, and apply the gelcoat generously, overfilling the area slightly. It's a good idea to buy some mold-release wax and apply it around the edge of the damaged area to prevent the new gelcoat from bonding to the old gelcoat. Failing that, tape the surrounding area.
After the gelcoat cures, sand out the rough spots with progressively finer grits of sandpaper until the repair is level with the surrounding area. Start by dry sanding with a 220 grit and go finer from there, ending up wet sanding with a grit of 500 or 600. The repair won't blend in completely, but over time it'll look less noticeable, until you don't see it at all. End the process with the application of a good-quality marine wax.
Unsightly scars, like the ones my Bristol got in the canals of New York State, don't have to be permanent. Repairing them isn't rocket science, but it does take time, patience, and the right combination of resin and/or gelcoat. With all the products on the market, it's easy to find the best one for any job.