Hi Glenn,
A twist bit would be fine - if you already have one that big. If not, don't buy one since they're expensive. A spade bit will work just fine, as will a hole saw. Depending on the thickness there, if you use the hole saw, you may only get part way through till the hole saw "fills up". In that case, remove the material from the hole saw (if it comes out with the saw) or chip the material from the hole and repeat. It's sometimes advisable to start the hole (regardless of which type of drill bit) in reverse - just till you get through the gelcoat. This will help to avoid chipping of the gel. With careful pressure, you don't really need to - but better safe than sorry.
I'm looking forward to seeing how this project turns out for you!
Hope that helps!
Dennis
A twist bit would be fine - if you already have one that big. If not, don't buy one since they're expensive. A spade bit will work just fine, as will a hole saw. Depending on the thickness there, if you use the hole saw, you may only get part way through till the hole saw "fills up". In that case, remove the material from the hole saw (if it comes out with the saw) or chip the material from the hole and repeat. It's sometimes advisable to start the hole (regardless of which type of drill bit) in reverse - just till you get through the gelcoat. This will help to avoid chipping of the gel. With careful pressure, you don't really need to - but better safe than sorry.
I'm looking forward to seeing how this project turns out for you!
Hope that helps!
Dennis