Use a Scraper before WetSanding
Use a 'Red Devil' scraper to remove the bulk of the bottom paint by hand, then wetsand with 150 grit wet-or-dry paper on hard rubber sanding blocks, switching off every few minutes to a second wet-or-dry on a sanding block kept in a 2 gal bucket with a couple drops of dish washing detergent. The slight bit of soap keeps the paper from building up paint residue. When you are down to clean gel coat folow Interlux's directions for solvent wash and apply 4-6 coats of Interlus 2000E. I use West System Foam rollers for a smoother finish. You will probably find the same description in the Interlux 2000 instructions.