FixorFish Loc: SW Oregon

Totally agree. Unless the fiberglass strands are being CUT, they will certainly "snag", pull, and create damage far beyond the intended hole parameter. This can also occur if your hole saw is not optimally sharp. Bite the bullet and buy a high quality (like "Starrett") hole saw. Most "Ace Hardware" stores carry them. By all means DO TAPE BOTH SIDES(if possible), but please don't use blue painters tape, not nearly as sticky as GOOD masking tape, the tan stuff (I use " Intertape Polymer Group" (IPG), I get it at the GOOD paint stores, like Sherwin Williams and Miller Paint...jmo, but 3M kinda sucks, & green Frogtape (good especially for paint masking) is better than most any "Ace", Scotch, or certainly Harbor Freight, rolls of tan.

If you, for some reason, decide to use a scroll saw (not my first choice if I need a hole that should be truly round, assuming you are installing some kind of flanged fixture...?), I would extend the masking to about 1 foot or more to prevent the saw's foot from scratches.
J from Cleveland's saw blade choice was a good one, but do hold DOWN tightly or it will jump on you.
Possibly a a better choice of blade, provided Bosch T-type blades fit the saw you use, is Bosch's T101AO. A kind of skinny, shorter blade (as are most "scrolling blades", only with very fine, non-hooked very finely honed teeth, much like a Japanese pull saw) (Dozuki)and most importantly....no kerf, the cut is the width of the blade's thickness. Because of that, use a slower blade speed, so as not to burn by speed. The other great thing about the Bosch blade is, UNLIKE the Japanese saw, this blade cuts on both strokes, great for fibrous &/or thin material, as well as minimal tearout on either side.

Hope at least a little bit of this is helpful to you or maybe someone else. Good luck on your chosen "task"...shoot some "before and after" pics for us, I believe we're all just a bit voyeuristic when it comes to projects like this, I know I am.

And, of course...be brave, you got this !

River Runner Loc: Austin

I was a boat rigger for several shops in my youth. Cut many 4-6” holes with hole saws and do not remember ever having issues, but in my personal shop I use blue tape on practically everything. Heat is the concern. We use liquid dishwashing soap as lubricant to keep from popping the gel coat when drilling, cutting or driving screws. Let us know how it goes!

Geemoe Loc: Channahon, IL

I worked at a marina some time ago. I always used hole saws for drilling holes in fiberglass. Standard hole saws for cutting through wood. You can tape the outside where the cut will be. Go slow when starting out. You should have no problem. Just make sure what is on the other side of where the hole will be. You don't need any surprises. Use a good marine seal when making the hardware secure. You shouldn't have any problems. Good luck, have confidence in you self....Geemoe

Geemoe Loc: Channahon, IL

Hey Tom did you cut the hole in your boat yet? How did it go if you did?....Geemoe