Also, looks like boat was left in water at lake for a long time. Anyone got the scoop on something that will clean the scum off easily? It's dried on hard and crusty.

 

What kind of hull?

I used a 3M paint stripper that attaches to a drill to grind off pits and stains on my aluminum boat hull.

I used a mild rubbing compound with carefully applied muscle power to clean up my fiberglass boat hull. It still has some yellowing but I'm not willing to go down too deep into the gel coat.

 

Thx, yeah it's fiberglass.

 

Muriatic (pool) acid in a garden sprayer. Let it sit for a few minutes then scrub it off with a stiff brush. Rinse it off the trailer immediately. Take the necessary precautions (rubber gloves, eye protection, calm day with no wind) and plan to toss the sprayer and brush when you're done because they'll probably be useless.

To bring back the hull's shine, wet-sand it with 600, 1,000 and 1,500 grit. Then use a power buffer with rubbing compound followed by polishing compound and finally a couple of coats of good wax. It's a lot of work, but once it's done it will require only power buffing and wax once a season.