Thanks for the replies but I've tried everything you mentioned exept the starbrite. From the waterline down its a brownish/greenish color. I noticed it last year when I pulled it out of a lake after fishing one day and wiped it with my hand, now the only place thats not discolored is where I wiped it(I know I should have wiped it down right away but thought I could wash it off at home, by then it was dry)It seems to be more of a stain than scum built up on the outside of the hull. From compounds,cleaners to chemicals I can't find anything in my shop that will touch it.I might have to take the fenders off my trailer and just try to buff it out. Any more ideas? Thanks