What component rotates and powers a boat forward and backward?

The propeller is the component that rotates and powers a boat forward and backward. Its blades are designed to push water in one direction, which propels the boat in the opposite direction. When the propeller spins, it creates thrust that moves the vessel, allowing for navigation and maneuverability on the water. Understanding the function of the propeller is crucial for safe and effective boating, as it directly influences the boat's speed and direction.

In contrast, the hull is the main body of the boat that provides buoyancy and stability but does not contribute to movement. A cleat is a device used to secure ropes and lines, and does not participate in propulsion. The gunwale is the upper edge of the boat's sides and serves as a structural feature; it also does not influence the movement of the vessel. Hence, the propeller is essential for a boat's movement, making it the correct answer to this question.