Please note that if you do the drywall sander/screen, you wet the surface first. Wet a few feet down with a hose and wash out the screen frequently. Actually pretty fast and it's dust free that way.Someone also had mentioned using a drywall sander & screen on the end of a wooden broom pole. Easier on the back & you're not covered in dust being under the boat.
Soon there will be a new stripper on the market. You paint it on, it works through the paint and separates it cleanly from the gel coat. This is environmentally benign and uses a patented biotechnology to separate the paint from the boat. Paint comes off in your hand in big sheets when you pull on it. It was demonstrated at the Miami boat show. They did a 60 ft boat in 6 hours. The other product (I dont recall the product) used on an identical boat took 3 days to strip. Not yet on the market. Note I do have a financial interest in this product.
We also have a bottom paint that that is environmentally benign and doesnt harm the animals. This is currently in testing with the US Army Corp of Engineers for use in controlling Zebra mussels in fresh water dams.
With any luck both products will be on the market within 2 years.