What part of a boat rotates to power it forward or backward?

The propeller is the component of a boat that rotates to provide the thrust necessary for moving the vessel forward or backward. When the engine of a boat runs, it turns the shaft connected to the propeller, causing it to spin. This spinning action pushes water backward, which in turn propels the boat in the opposite direction, following Newton’s third law of motion—every action has an equal and opposite reaction.

The gunwale refers to the upper edge of the side of a boat, which provides structural integrity and serves as a lip for holding equipment but does not contribute to propulsion. Freeboard is the vertical distance from the waterline to the upper deck level, influencing stability and safety but not affecting how the boat moves. A cleat serves as a tie-down point for securing ropes and lines, playing a vital role in mooring the boat but not involved in its forward or backward movement.