I always try to minimize the amount of holes we drill into our boat, but every now and then a hole is necessary to mount a new accessory. To prevent gelcoat and fiberglass from chipping or creating spider cracks, follow these steps.
Using blue painter’s tape, mask off the general area where you will be mounting the new accessory. The tape will avoid scratches and provides a good background to make your marks for drilling.
Remember, measure twice, drill once! It’s a tried-and-true philosophy that you really need to embrace when you’re about to drill into your boat.
How to Drill Holes in Fiberglass
Mask the base of accessories as well since you will be sliding them around as you measure and center.
Mark one hole when you are certain of the location. We drill a small hole and put a screw into the first hole before marking the others in case of slight shifts when drilling.
Drill a very small pilot hole in the dead center of your mark.
Next, use a countersink bit to grind out the area around the hole, not too deep, you are not really countersinking the screw. This is the key to eliminate larger chips of gelcoat from breaking out when you drill the true size.
Fiberglass does not expand like wood so choose a bit that just catches the threads of the screw. Screw in the first screw firmly and now mark or drill tiny pilot holes in the remaining spots. Remove excess material and then drill the full size of the hole. Dry fit everything before you break out the caulk.
Now peel off the painters tape, degrease with a solvent like denatured alcohol. Use a caulk with the appropriate properties for UV exposure, holding power and removability. Use enough caulk to get a good squeeze around the edge and around the screw holes. Put a dab on the threads of the screw as it goes in so it will seal completely. Wipe away excess caulk with lots of small pieces of clean paper towel. Wear latex gloves to minimize the mess you make on your hands, as well as the boat.
Give the caulk time to dry.