Not sure what would be best to use. No metal drill bits that large. Flat wood bit? Nah. Hole saw, don't have anything that small. Should I go find one? Will fiberglass dull hole saw, if not high dollar one?

Go to Home Depot and buy a hole saw. The run it in reverse. It will cut slow but leave a nice edge. Or find a uni bit.

hole saw... run it in reverse to cut thru the gel coat, then forward the rest of the way and very little pressure. Also, rock the dril around in slow circles while cutting. It will keep the holesaw from grabbing and causing the drill to want to rip right out of your hand.

A flat wood bit works perfect just take your time run it slow and hold the drill good

If you have to go buy a bit you may as well buy one of the auger bits. It looks like a screw at the tip and turns into an oversized drill bit, but has a flat head right after the screw portion. Those things kickass, and drill perfectly shaped nice holes.

Not to be picky, but if you use a 7/8 holesaw and rock it around, you're going to end up with a hole that is larger than 7/8ths of an inch. I don't know what your tolerance is for being off a little bit, but your most accurate results will probably come from that auger bit.

Hole saw definitely.

Unless it is CSM layup, anything other than a hole saw will grab the fibers and tear them out.

Yes, I agree with holesaw. I've cut from 3/4" up to 6" holes in glass and carbon using standard holesaws, no problem. Use masking tape on the gelcoat to keep it from chipping. I've never tried running in reverse through the gelcoat, but I'll give that a try next time I have the need.

Ditto with Maritime & Panther , it will be easier then you think and use some masking tape ....

Hole saw it is! Thanks guys.

I'm plumbing in a flush kit and mounting garden hose fittings on lip inside engine compartment.