Hello,
I recently purchased a pontoon boat that was lake kept in a dock and the lower unit and prop have a lot of calcification on it that i cannot get off. I tried white vinegar, CLR and StarBrite Hull Cleaner. None of these products are even starting to remove the build-up. Anyone have a solution? Thanks in advance.
Donnie

Lime away works.
I could see the need for a wire brush if it's really bad.

I haven't tried this for this application but muriatic acid is what they use for pools and fountains. Does wonders for toilets. It should not strip the paint but it could etch it, best to spot treat an area first. You can find it at Home Depot or pool supply store. Oh and you shouldn't use this over concrete.

30% cleaning vinegar. I use this diluted in a spray bottle to wipe down the boat or straight to treat the really pesky water spots. You can find this at Home Depot too. They also sell higher concentrations online.

Pat mentioned Lime-a-way. My wife used the gel version and let it soak to clean the kitchen sink. It discolored the stainless. Just thought I'd mention that in case you have a stainless prop, but it shouldn't be an issue if you're rinsing it off frequently.

You can knock off as much of the heavy deposits with a hard plastic scrapper. It's gonna take alot of elbow grease and a stiff bristle brush. You may want to go look for the Ben-Gay first. LOL

Lime away

I have some on the sides at the back of my boat. I have thought of using lime away on mine also. The very back of my boat is like new (95 model) and never had any scale on it period. Never understood why it stay so clean.