What is Pitch?

Pitch is the distance a propeller will drive through the water in one revolution, just as a screw will into wood, visible as the angle of the blades away from the axis of the propeller shaft. For each revolution the propeller actually pushes the boat forward a distance a bit less than this nominal face pitch.  The difference in these distances is called slip.

An increase in pitch allows the propeller to grip a larger amount of water, a decrease in pitch reduces grip in the water.  Small pitch propellers, like a fine thread screw, take many turns for each distance forward (effecting lesser forward movement for each rotation).  Large pitch propellers, like a coarse threaded screw, take fewer turns for each distance forward (effecting greater forward movement for each rotation). 

Small pitch for larger displacement vessels, like harder dense wood (greater force) needs a fine thread screw.  Large pitch for smaller displacement vessels, like softer wood (lesser force) can use coarse thread screw.