Automatic River Flowmap Blueprint/material

I like it. If I were to place an object (raft, cube, person_actor, etc.) will it have buoyancy with proper physics or will it sink? The reason I ask is: I just finished the rough draft of game progression design. It will use a river, a raft (or some type of wooden boat). The river at first will be very calm, then the middle will be rather rough, the end an ocean.