I have an 18ft Sylvan sportsman with a painted alum hull. Go to walmart and buy the Atwood hull cleaner. You can pour it into a spray bottle and spray it on the one side of the boat. Let it sit for a couple minutes, you can work some areas with a sponge to loosen. Spray it off everything, towel dry. This stuff works great! It is a mild acid so make sure you rinse good. Then I wash again with car soap, drip dry then spray wax and hand towel dry. Makes it look new again. Mine is an 84 and it looks much newer.
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