What propulsion device did Leonardo da Vinci study for a boat?

Leonardo da Vinci studied paddle wheels as a propulsion device for a boat.

Leonardo’s notebooks contain designs for boats driven by wheels fitted with paddles. Turning the mechanism would push the paddles against the water and move the vessel forward. His drawings explored ways to transfer human effort through gears and shafts to the paddle wheels.

Paddle-wheel propulsion was not unique to Leonardo, and his sketches did not create the successful steam-powered paddle steamer. Ancient and early modern engineers had already considered water wheels and related devices. Leonardo’s contribution was his detailed mechanical analysis and his attempt to adapt the idea into a practical boat design.

The idea should not be confused with the screw propeller used on most modern ships. A paddle wheel works with broad paddles at the side or rear of a vessel, while a propeller uses rotating blades beneath the water. Leonardo investigated both water transport and mechanical power, but the paddle-wheel boat is the clearer example of his interest in direct wheel-driven propulsion.