Last year, I shelled out 8 bucks for a hull cleaner from Starbrite. When I got it home and used it, I discover it is primarily oxalic acid whic is wood bleach. Oxalic acid is obtainable at the local hardware store. It is made by Savogran and others. A small 12 oz container costs about $6.00. Use a heaping tablesoon in a gallon of hot water. No other soap is needed. Takes fresh water scum off like magic.The small container would clean 25-30 boats. Use a sponge or a scourpad like you do dishes with. A pair of rubber gloves are handy.