That's what I used to clean my hull,it works. Be sure to rinse everything off well with water to dilute that acid down.
If you have that white calcium buildup on your motor and lower unit try using the toilet bowl cleaner "the Works". I just used that on my honda tonight. Squirted it right out of the bottle,and let it run down the lower unit. It foamed up all the way down taking the calcium with it. It just melted off like it was sugar. Rinsed everything down good,and the paint looks like new.
I wouldn't try any of this on a nice concrete driveway. It will etch it.