Soda blaster
If you have a heave build up of a hard bottom paint, the absolute best way is to soda blast. It is fast, environmentally friendly,non toxic, and washes away with the first rain.The only one I have done this way had many years of a hard bottom paint on it. After three or four days and several gallons of stripper, had made little headway. I rented a soda blaster. It was fairly expensive, but probably not much more than the many gallons of stripper it would have taken.The whole job took about three hours on a 28', and it was down to the gel coat, ready for paint.