Cleaning up an old boat

Have become the owner of a 1986 16 FT. thundercraft bow rider.
Sold and clean interior but the Hull leave a lot to be desired.

I'm trying to get the tanned bottom back to white and have tried various gentle approaches so no looking at a product called Slime Be gone.
It's very similar to Slimy Grimy and find myself nervous as to it getting on me or my trailer and the run off impact on the environment.
Comments of experience with this product appreciated.

As follow up question how clear of stain must the hull be before it can be painted?

Thanks

Muriatic acid should work,read cautions on bottle, must be diluted

Thanks