if its a glass boat i would start by just scoring the glass and peeling it off before cutting the wood.
also dont go too close to the edges until you are sure of whats underneath.
I also found when i did mine that rather than putting the new floor down then glassing it, i glassed the underside of the floor leaving a few inches of clorh overhanging. once you put it down the right way up this gives you material to bond to the edges, then when you glass the top in it all locks together. I used 9 mm ply and it comes up rock solid this way

cheers

* Have a particulate and gas mask.

* Wear glasses and ear muffs.

* Wear gloves

The best cutter I found was some thin metal disc that goes into an angle grinder (at least 5") in conjunction with a push-pull saw. Use metal blades, the wood ones go blunt too fast and I can't remember if the pull cut or the push cut ones were better, but there is a big difference.

You can usually stamp around on the floor to find a bearer, drill between the bearers, put a bent wire down to check if there is nothing either side, then start cutting till you can look under the floor.