I would get it up on stands where you can work on it, get your respirator, this is some nasty stuff, I just finished my 245 Osprey. Most anti-fouling ablative paints are made to go over other bottom paints without removing the old completely. You need to sand the entire bottom with 80 grit, use a random orbital. Hopefully you will see that most of the exisiting paint is adhering well enough to leave it alone, feather the edges where the bottom paint has been completely removed and only gelcoat remains, this will result in a smooth transition and not show large pitted areas. Then re-coat with your choice of bottom paints, my choice would be the interlux vivid paint line. It is a very bright and hard antifouling paint, it won't chalk like some and it will last you a couple years at least.
If the majority of the bottom paint is coming off during your sanding evolution, then take it all the way down with the 80 grit to the gelcoat, your other alternative for complete removal is chemical stripping with peel away or some other fiberglass safe paint stripper, there are several out there. Once stripped you would go back with an epoxy barrier coat paint and then finish the same as above with the anti-fouling paint. Good luck
Marc
