What is Prop Walk?

Prop walk occurs when a turning propeller pushes a boat’s stern sideways. A single right-handed fixed propeller will tend to push the stern of a vessel to starboard when going forward and to port when going in reverse.

Prop walk affects most single-engine vessels. Also known as “asymmetric blade thrust,” prop walk is due to the downward propeller shaft angle being not parallel to the water’s surface (most sailboats’ shaft angle is between 8 and 14 degrees) creating difference in the cylindrical distance traveled by the propeller blades on their upstroke versus the downstroke. The water at the bottom of the propeller is a bit denser and freer to flow (there is no hull above it) than at the top of the propeller. The upstroke of the lower blades is a bit more effective pushing more water, generating more thrust on that side. The lateral deflection off the hull, pushes the boat’s stern sideways, pivoting the vessel around a point located about one-third of the boat’s length aft from the bow. The propeller and the stern “walk” sideways in the direction of rotation.

A single right-handed fixed propeller will tend to push the stern of a vessel to starboard when going forward and to port when going in reverse.

There are a number of factors that contribute to prop walk in reverse. In reverse the boat acts like pushing a grocery trolley backwards, it is more critical to steer as any very small movement of the wheels gives a big course change – the same in reverse as to where the rudder is located in respect to the boat and keel.