Leonardo da Vinci designed a paddle wheel to propel a boat, replacing repeated strokes of individual oars with rotating paddles that push against the water. His notebooks contain several studies of paddle-driven boats and transmission mechanisms.
The designs used gears, cranks or treadles to transfer human effort to wheels mounted at the sides or stern. Leonardo was investigating how continuous rotary motion could make propulsion more regular and allow several paddles to work in sequence.
A paddle wheel is different from a screw propeller, which uses a rotating helical blade beneath or behind a vessel. Leonardo’s sketches were experimental concepts, and no surviving evidence proves that one of his boats completed a voyage. Paddle propulsion later became practical on river steamers and other nineteenth-century craft.