TECHNIQUE How to tell if your propeller is left-handed or right-handed

The evolutionary effect of the propeller is an important aspect that we will always have to consider when maneuvering. The evolutionary effect of the propeller is the displacement that its rotation imparts to the stern of the boat due to the friction generated with the water. When the propeller rotates to the right, it produces a force directed to the right of the stern, and vice versa when it rotates to the left. Thus, there are propellers with “right-handed” characteristics and propellers with “left-handed” characteristics.

Contrary to what semantics suggests, the former provide greater ease for the hull to pull to the left, the latter to the right. The greater or lesser strength of this effect will depend on the shape of the hull, the size of the propeller, the number of blades, and its position relative to the center of gravity of the keel and the rudder axis.

Wanting to go to extremes, a flat keel, a thin centreboard, a large propeller whose axis is positioned in the aft section of the boat will produce a great evolutionary effect.

How can we tell whether the propeller mounted on our boat is right-handed or left-handed? A fairly simple method is to position the stern to the wind, engage reverse gear, and increase engine rpm. If your bow pulls to the right and your stern pulls to the left, your propeller will be right-handed and you will immediately know that the most maneuvering side of your yacht will be the left.

In this case you will need to consider approaching all reverse maneuvers by pulling the bow slightly to the left to anticipate the stern’s tendency to go to the left at the moment you engage reverse (the so-called “tail stroke”). Therefore, by knowing the evolutionary effect applied to your boat, you can more easily understand which side to approach a mooring from.

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