What Leonardo da Vinci device used rotating paddles to help move a boat?

Leonardo da Vinci’s powered watercraft concept was a paddle-wheel boat.

Leonardo designed boats that used rotating paddle wheels to push against water and propel a vessel forward. The wheels were connected to hand-operated mechanisms, allowing people inside the boat to turn them. His drawings show an attempt to replace or supplement ordinary oars with a mechanical propulsion system.

The concept reflects Leonardo’s interest in applying rotary motion to transportation. Gears and cranks could coordinate the wheels, while the hull carried the mechanism and its operators. A paddle-wheel system can produce thrust without repeatedly lifting oars from the water, although its efficiency depends on the wheel design, power available, and operating conditions.

Leonardo did not invent the general idea of paddle propulsion, and his boat was not a steamship. Steam-powered paddle boats appeared centuries later after advances in engines and metallurgy. Leonardo’s design is best understood as a Renaissance human-powered craft that anticipated a principle later used in powered riverboats and ships.