Greased Lightening - Warning!
Greased Lightening is the only thing that has worked for me. Let is sit for short time and wipe with rag. If it gets on fiberglass, it will turn yellow and you think you have stained your finish, but it is only reacting with organics on the surface and will go away. BEWARE, though. It is very, very slippery. While cleaning my swim platform area, I got struck by Greased Lightening and was in the water before I knew what hit me. Guy on the next boat said "Get the gaff, Della, Bob fell in." OOPS!