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How do I fix the cracks in my hull?

2014 May 5

Dear Boat Doctor,

I'd like to start sailing my older MFG Pintail daysailer. The boat is complete but it has a couple cracks in the hull. The cracks go all the way through the hull and are about 2 feet long. It's an older boat and I am not greatly concerned with cosmetics, I just want a solid hull. Can you give me some tips on how to make this repair?

Clark Case

Aurora, Ohio

Dear Clark,

This repair should be very manageable. Since the cracks are all the way through, the first step is to grind the broken fiberglass back into solid unbroken material. Go at it with an electric grinder or very coarse sandpaper. Aim for a 12-to-1 taper on the fiberglass, so for the thickness of your hull, this is 2 to 3 inches past the repair. Once you have all the bad glass out and the taper sanded in, wipe it down with acetone to remove any dirt or grease.

Since you will have ground all the way through the hull, you need to make a backer to fiberglass on top of. Good old duct tape will do the trick, just tightly tape over the hole in the hull from the inside, a couple layers will contain the fiberglass.

I like to do fiberglass repairs with epoxy; it costs a bit more than fiberglass resin but is much stronger. I use West System (www.westsystem.com) epoxy, but there are several other brands on the market that will do the job. You'll need epoxy resin, hardener, four-ounce fiberglass fabric and some epoxy fairing thickener.

There are two methods to lay up fiberglass: wet and dry. With wet lay up, you saturate the cloth with resin and then apply it to the repair. Using the dry method, you lay the fabric on dry and squeegee resin into the dry fabric, saturating it in place. Either method works, but I prefer to use the wet method. I find it handy to presaturate my fabric in a disposable paint roller pan.

You'll need to cut fiberglass cloth to fit the repair. Start with pieces that completely cover the area and then use smaller pieces as you build up the repair.

The first step is to "wet out" the margins of the repair by brushing the tapered areas around the repair with epoxy resin. Then layer in presaturated fiberglass cloth, filling in the repair.

After the patch dries overnight, scrub it with water to remove the amine blush (a by-product of curing), and sand the patch smooth with 80-grit sandpaper. You can remove the duct tape from inside the hull and sand the patch on the inside too.

Next, mix epoxy with fairing thickener to a peanut butter consistency. Use this material to fair the patch smooth, inside and out. Sand smooth with 80-grit after it dries. At this point your patch will be complete, but finish up the job with a bit of paint.