Is it a car motor or a boat motor? If it is set up for a car, you will need to do some work to it. Boats really need different cams than cars in order to perform well. The torque curve that you get out of a street cam is wrong for the water. There are a few other odds and ends (different freeze plugs, marine starter, etc) that need to be done as well.
Will a car motor push your boat through the water? Yes. Should it? No.
That being said, I'm sure there are 50 members on here that have car motors in their boats and love them.