I have a boat scheduled for this week. The boat is fiberglass and less than five years old with a little oxidation ( it is red) i can handle that, the problem is there is a layer of gunk just below the water line, it seems pretty thick. it feels like sand and mud. is there some kind of special boat cleaner designed to clean this stuff?? I was thinking of just scrubing my arm off with diluted simple green??? any advice would be appreciated.