Yep, they are called a jet ski!
As smokeonthewater mentioned, there is more to the story than pure horsepower. And if you do go down the route, start with a PWC engine and modify from there, at least a lot of the hard stuff (cooling system & marine certified components) is already done.
Ayuh,..... For the sake of conversation,..... I believe that the modern high horsepower outboard motors can't be beat for Pure Horsepower,.....
Pound for pound, Pure Horsepower to weight ratio,....
Consider, a screamin' Big horsepower snowmobile motor don't weigh much, but it ain't got it's built in driveline to the prop,....
A jetski is 'bout the closest ya get, 'n they've been transplanted into 'bout every hull that'll float,....
Big outboards, now-a-days need big hulls to float 'em,.....
Back in the ole Tower of Power days, you could hang 150 hp, on some pretty tiny hulls,....
'ell, I had a 135 hp on a 1967 Glastron 14' Jet-flite, in the '80s/ '90s,..... still got the hull, 'n a 150 hp mothballed to go on it,....
