Re: alum boat help
The best place to start is with an acid based pontoon boat cleaner, like ToonBrite--available at any boat dealership. Spray it on, hose it off. You might also have to go the ScotchBrite pad and a strong cleaner to finish the job.
Sharkhide is a thin, clear protectant to maintain a clean, polished finish. They also make an aluminum cleaner, but it's not easily found on retail stores' shelves.
It'll usually get the hull clean but leave a dull finish. If you don't like the finish, any unpainted aluminum boat can be polished for a better shine. I use a 6" wool bonnet on a Porter Cable Dual Action Polisher and White Diamond metal polish (Advance Auto Parts).
My pontoon boat is a near mirror finish.