Re: Floor removal with fiber glass over it.
I always select a spot away from a stringer. Judge that by looking at the sides of your bilge. Go a couple inches past where the stringer should be, at the edge of the bilge. Use a hole saw or something similar to cut out a small area...I like to do this to see the thickness of the material I'll be cutting. Then using a circular saw set for the floor thickness, cut the floor out in small sections.
I like to cut area's about 2 feet square. You want something easy to handle, plus it gives you a look underneath of what you'll be cutting next. You want to know where all under-deck plumbing, wires, etc are, to avoid doing even more repairs. WEAR proper safety equipment, and not a paper mask. Spend to 40 bucks for a quality respirator wit the catridges. Be ready for a big mess, and you might as well be prepared for the worst. (Wet foam, rotted stringers, transom, etc.) Keep in mind, this is like finding a soft spot in your kitchen or bathroom floor. Want appears to be a cheap, $100 fix turns out to be the tip of the iceberg. If it's just the sole that's soft, and you happen to get lucky....count your blessings!