Maybe I have missed the boat here ( no pun intended ) on cleaning good old river scale off your boats white hull but I have been using bar keepers helper with a spray bottle of 1/2 water and 1/2 vinager with excellent results! I'll spray the area with the water mix first then on a rag sprinkle the bar keepers , water it down and then with a little elbow grease attack the area with the rag and rinse off with the water mix. Simple but very effective. Doesn't scratchave and what an amazing shine. Yes you have to wax again but it's clean!
Sorry to those who have known about this for the last 100 years......it always gets to the Midwest last! lol