How do I cut a fibeerglass boat hull?

Question

I bought some new speakers for my boat and they are a little bigger than the old ones and I need to cut the hole larger. How can I cut a larger round hole?

Answer 1

I'd suggest covering the entire area with masking tape prior to making a cut if you are cutting through gelcoat (the stuff that covers the hull is also gelcoat). This will prevent scratches on the surface. Measure carefully and mark the pattern on the tape. If you are mounting speakers in an area covered by carpet consider removing the carpet from that area and cutting the hole first in the fiberglass, then replace the carpet and cut it with a sharp knife. Round holes are best cut with a hole saw and a drill, ovals can be cut with a jigsaw or sabre saw. Blades that are thinner, teeth to back, are easier to turn corners with. I used to rig new boats and believe me, no matter how hot it is wear long sleeves and pants! Cold water seems to help wash out those tiny little prickers too.
By all means check behind where you're making holes in your boat!

Answer 2

Any saw that will cut wood will cut fiberglass. Any saw that will cut metal will cut fiberglass. Wood blades have fewer teeth per inch, so they will cut faster, but have a tendency to chip the outer layers of the fiberglass. Metal blades cut cleaner but slower.

Dangers to watch out for, cutting fiberglass produces dust and glass fibers. It will irrate skin, eyes and lungs.

Other things to watch out for, make sure nothing is behind the panel youre cutting, as example, speaker wires, control cables, 12v wires etc. Also check that the part your cutting doesnt get drastically thicker, indicating a structrual member. Watch out for metal screws or small metal plates that the speakers screw into.

One other tip, after you cut the hole. seal the cut with fiberglass resin or a water proof paint. This is especailly needed if you see any wood, balsa or foam in the middle of the fiberglass sandwich.

Answer 3

Fiberglass is no fun to cut. You may mark your circle and use a Jig-Saw. Do this outside not in a garage. May use a fan to help blow dust away from you. Some people rub a thin amount of Vaseline on the Face, Neck, Arms etc. and shower after-wards. You get this stuff in your skin and it no fun. You will live but not too happy for a few days.