I've got a model from my friend's estate that's a commercial model from Northern Tool that has a 5 hp 240 volt motor, pumps 4 gpm at 2750 lbs, and with the turbo nozzle (an extra $200), will blow the pinstriping off your car, clean just about anything, or kill small varmits, if you prefer.
Boat bottoms can be tough, though, especially once the salt water creatures cement themselves on. Will remove old bottom paint, too, in many cases.
The turbo nozzle doubles the efficiency of the washer, pulsating the pressure to loosen the offensive cling on stuff.
Most of these bigger units are two handers, though. You wouldn't want to try to control one with it's thrust with just one hand.
Mine comes in an alternate, but otherwise identical form with an 11 hp Honda motor, which means they can use an electric motor at 95% or more of it's full potential continuously, but can't do that with a gas engine and the considerations for heat build up, engine life expectancy, etc.
Get one with a siphon feed for soap, solvent, insecticide, disinfectant, or classified military solvent co-use. No telling what you might have to use it for someday.
Works great inside the cockpit, too, just don't let it blow anything apart you don't want to separate. It's the only one thing I know that will blow out the crap that settles under the fuel tanks!
I also built a 50 foot extension cord of #8-4 black rubber covered cord, and the original 30 feet of cord on the machine has a built in circuit breaker with GFI circuit, additionally, to protect you.
Get yourself a heavy duty water hose, too, so you can feed hot water from the top of the water heater and turn the temperature up to about 180 degrees (temporarily, of course), and you can again double the effectivess of the unit.
Set your house, garage, RV barn, and whatever else up with 220/240 volt AC single phase power for it's use. This is a bit of extra $$ and work, but then you don't have to drain the gas, etc., that you have to do with a gas motor, either.
Use it on the boat bottom in a sloped driveway if possible. That way you can send all the smelly stuff off the bottom of the boat down and over to the front of your neighbor's house for them to enjoy. My wife hates the smell of decaying algae and aquatic plants mixed in with the aroma of her prized roses.
Have fun with your new toy!
Joe. :teeth :thup