How does a motorboat use a propeller to move forward?

A motorboat moves forward through the use of a screw propeller, a device featuring a central hub with radiating blades arranged in a helical, or spiral, surface.1

As the propeller rotates, it imparts sternward acceleration to the water, which generates thrust and propels the boat forward. This process relies on pressure differences created by the blades: the rotation causes a reduction in pressure on the advancing side of the blade and an increase in pressure on the after side. Because the pressure reduction on the advancing side is typically much greater than the pressure increase on the after side, the blade effectively pulls itself through the water.12

The total thrust produced is proportional to the mass of the water acted upon and the rate of acceleration. For maximum efficiency, a propeller should act on a large mass of water with minimal acceleration, which is why larger-diameter propellers are often preferred for optimal performance.12