Fluid Effects > Ocean > Add Boat Locator
 
 
 

Boat locators follow the motion of the ocean in the Y direction, but additionally rotate in X and Z to allow the boat to pitch and roll in the waves.

Fluid Effects > Ocean > Add Boat Locator >

If you want to move the position of the locator interactively, the locator cannot be connected directly to the expression. In this case, turn on Free Transform.