Cutting Fibreglass?

[steve_n]

I want to plumb up the bait tank in the back of my boat, it has one of those built in jobs with lid. I've seen the overflow set up as a horizontal slot straight through the back for the water to run out. How would I go about cutting one of these slots without chipping the gelcoat on the outside? I'm not sure whether to try and drill some holes and then file or cut a slot with a grinder. Has anyone tackled this job before? After the jobs done should I coat the cut surface with a paint or sealer.
any advice greatly appreciated.
Thanks Steve

[billfisher]

An angle grinder with a diamond cutter does a pretty neat job. Make sure you use a respirator though. Those paper dust masks are not good enough.

[finga64]

there is also a blade available for the little angle grinders that looks like a normal tunsten tipped saw blade. They're great for cutting fiberglass and if you lubricate them with some soap they really good for cutting aluminium.
They do a neat job as well. No chipping on the gel coat
Make sure you use a blade guard though as they would be really, really bad on the knuckles