Like Strick, we have a Cat piston pump coupled to a Honda 9 HP, purchased from
Northern Tool. It has 5 nozzles. There are 2 nozzles that are perfect for boat hulls, but you have to be careful not to blast off the bottom paint (unless you want too, because it will). Works great on non-slip too. There is one nozzle that's only purpose is to cut human flesh. We try to stay away from that one.
Gas is noisy compare to electric, but you can put this in the the back of the truck and make it work anywhere. We use a 500 gallon poly tank to give us over 2 hours of use on remote jobs.
I also have a
Karcher Electric Cold Water Pressure Washer . It works well cleaning up the boat, but is not strong enough for bottom jobs. There are several to choose from in between.
If you rent or borrow a couple different ones, you'll know what you need. This is not an 80/20 rule decision. The pump, because it's adjustable in pressure, flow and RPM's (gas), you need one that will do the most difficult job you anticipate in any typical season.
Northerners be sure to winterize them or don't let them freeze.