What device did Leonardo da Vinci design to help ships move through shallow water?

Leonardo da Vinci designed a paddle wheel to help ships move through shallow water.

Leonardo’s naval studies included vessels propelled by wheels fitted with paddles. As the wheel turned, the paddles pushed against the water and produced forward motion. Human operators could power the mechanism through cranks or related gearing, making it an alternative to oars.

The idea was attractive because a paddle mechanism could concentrate many strokes into a compact machine and potentially reduce the number of exposed oarsmen. It was not a practical replacement for later steam-powered paddle wheels, which required a much stronger and more reliable source of power.

Leonardo’s wheel is sometimes described as a propeller, but a paddle wheel works by pushing water with visible blades mounted around its rim. A screw propeller uses rotating helical blades below the waterline.