Re: Enlarging hole in hull
Oopsie arbor: damn, I need to buy another neat new tool I never heard of before!
The block of wood to allow a new hole saw with pilot is the conventional way to go, but you can also often skip that by running the new larger hole saw IN REVERSE to score the hull and get a ring started. If you do that very carefully, once you have the ring started you can go into forward and just cut through.
Of course, the block of wood and new pilot hole eliminates a whole world of possible errors. Use a hot glue gun to attach it, and you can pop it off easily afterwards.