My father in law asked a tech at a Marina/boat repair shop after his boat got messed up from dock rash what he used to get any hard water off of it, CLR diluted with water is what he was told.
I recently bought a 16' side console myself and it had pretty good buildup on the hull. I used ¾ water to ¼ CLR and sprayed it on, everything came off great with a little soft scouring pad scrub