I have always used Soft Scrub (with bleach) with great success to remove stubborn stains and oxidation on fiberglass hulls & non-skid decks. From my experience, Soft Scrub even bleaches the black dingy stuff off untreated teak, giving it that golden, new look. The smooth fiberglass areas should then be followed with a wash and polish to regain and protect the gel coat's shine. I buy the stuff by the case. Use caution on painted surfaces. Scott Simpson West of One 300 3rd Street, # 903 San Francisco, CA 94107 415. 328.2668 scott@westofone.com www.westofone.com