Marykate On & Off / Hull Bottom Cleaner 1 galloon 4 per box Available for delivery This powerful, acid-based cleaner is a proven way to deep clean and remove a wide variety of stains from gelcoat. Typical uses include the removal of waterline rust and scum stains. Do not use on aluminium surfaces. Key features Removes rust stains and waterline scum Brush-on/rinse-off, biodegradable formula Will not harm fibreglass, gelcoats Works instantly to remove the toughest waterline stains