What marine propulsion device did Leonardo da Vinci sketch with rotating blades?

Leonardo da Vinci sketched a screw propeller as a marine propulsion device.

His drawings show a helical, screw-like structure intended to push against water and move a vessel forward. The idea appeared among his studies of boats, water flow, and mechanical motion. It applied the same general principle as a screw: rotation could produce forward movement through a fluid.

Leonardo did not build a powered ship using the design, and the sketch is not a modern propeller in its final engineered form. Later marine propellers developed through separate work by inventors and engineers, including practical designs in the 19th century. Steam engines and improved metallurgy were also needed before screw propulsion became widespread.

The design is sometimes confused with Leonardo’s paddle-wheel studies. A paddle wheel uses broad paddles that strike the water, whereas a screw propeller uses helical blades rotating around a shaft. That distinction makes the screw sketch especially significant in the history of marine propulsion.