How do propellers work in boats and submarines?

A propeller (or screw in marine terminology) works the same on boats and submarines as on an aircraft so fitted. In the water, the screw converts rotary motion into forward (or reverse) motion. We see blades that are inclined or tilted to meet water on the leading edge and push that water backwards along the face of the blade and off the trailing edge. Pushing the water back pushes the marine craft forward in the water per Isaac newton.