> Wishing there was a way to support the edge
> as you get close to finishing the cut, I got a little bit of tearout
> there.

What you can do (on your wife's boat), is after cutting about half of the circle of the hatch, stretch a piece of duct tape across the hatch and onto the deck on both sides. When you finally cut through, the hatch won't drop. Also, you can cut the final 1/8" by hand using a razor saw or a jigsaw blade held in vicegrips.

> I had to justify at least one power tool purchase ;-)

I just love that part.