What boat-propulsion device did Leonardo da Vinci design using two large paddle wheels?

Leonardo da Vinci designed a paddle-wheel boat using two large paddle wheels for propulsion.

The design appears among Leonardo’s studies of watercraft and mechanical engineering. Rotating paddles would push against the water and drive the boat forward, offering an alternative to conventional oars. The arrangement reflects Leonardo’s effort to convert rotary motion into useful movement on water.

Leonardo’s boat concept belongs to a long history of paddle propulsion, which later became important in steam-powered vessels. His drawing, however, does not prove that he built a working powered boat. The source of mechanical power in the proposed design is also not equivalent to the engines later used in commercial paddle steamers.

This craft should not be confused with a screw-propelled boat. A paddle wheel acts at the water’s surface with blades or boards, while a screw propeller rotates beneath the water like a helical fan.