Removing antifoul

Can anyone offer a suggestion as to the best antifoul paint stripper. I bought some so called specialist product but it hardly touched it. I don't wont to scrap above the water line as it result in some gelcoat damage. Help please??

Mask off the water line if you must use a scraper. Otherwise use a nylon scrubber, which won't damage the gel coat, and remove the loose antifouling, leave the base layer and overcoat with new (compatible) antifoul