The Best Ways to Cut a Fiberglass Boat

by John Willis
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For repair or modification on your fiberglass boat, you may need to cut through hardened fiberglass. Whether you're cutting through hull fiberglass, supports, deck or superstructure, fiberglass boats are heavily built with glass and hardened polyester resin. Resin and glass dust from cut resin is a health hazard that should not be inhaled, so you should wear a respirator.

Start with a Hole and Scribe

If you're cutting a hole to install a new window for example, you want to cut just the right shape: not too much, requiring difficult patching and not too little, requiring laborsome filing and sanding. To do this, use a template and carefully scribe the pattern onto the fiberglass. Using a template may be much more accurate than trying replicate the measurements of a complex shape. Scribe it with a fine-tipped permanent marker or anything that will be easy to see even with a little fiberglass dust on it. Drill a starter hole for your saw blade. If your shape has even radiuses, consider using a hole saw for them, then connecting them with a straight-cutting technique.

Cut-Off Wheel

A cut-off wheel with a thin, abrasive disc is or metal disk with a fine-toothed edge is a great fiberglass cutting tool. In fact, it's very similar to a doctor's method of cutting off fiberglass casts, only you'll be using an angle-grinder instead of a small rotary tool. Be careful when using a cut-off wheel though, as you'll have to apply pressure perpendicular to your cut, making it easy for the wheel to bind or wander off your cut-mark.


A jigsaw is plenty capable of cutting fiberglass in fairly small quantities if you have a sharp, aggressive blade with deep grooves in the teeth. Start the jigsaw in the pilot hole you drilled. Move steadily along your cut-line. It's more controllable than a cut-off wheel, in part because it has a flat base that presses against your work surface.

Reciprocating Saw

A reciprocating saw, sometimes called a saws-all, is essentially a very large jigsaw. However, it is more powerful and the blades are larger. Like a jigsaw, its effectiveness depends on your choice of blades. You want something rigid that won't bind. You want sharp teeth with enough hook to clear the cut fiberglass shavings. Make use of the triggers as controlling the speed of the blade will help you control your cut.

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