Y10 Fibreglass Stain Remover Net Weight 280g. Y-10 rapidly 'absorbs' yellow/brown waterline & transom stains on white or light-coloured fibreglass boats. Also effective against rust stains & may be used on painted boats Directions: Spread a thin coating of Y-10 over the stain, wait a few minutes while a mild chemical reaction causes the stain to vanish, then wash it off.
eBay