You can make an object float like a boat by adding a boat locator to it. Standard boat locators behave like dynamic locators, but also rotate in X and Z. Motor boat locators include throttle, rudder and roll attributes to realistically simulate the motion of a motor boat.
Fluid Effects > Ocean > Make Motor Boats > 
If you want to move the position of the boat interactively, the locator cannot be connected directly to the expression. In this case, turn on Free Transform.
