Propeller installation is an important factor determining a boat's performance. While many racing boats have a folding propeller to minimize its drag, there can be a considerable difference in drag if the boat has a strut drive or shaft installation, just as there is a difference in drag for fixed, feathering or folding propeller blades. This is all defined by the propeller measurements.

Propeller types

Solid Propeller Solid Propeller
Folding Prop Folding Propeller
Feathering prop Feathering Propeller

Propeller installation types

1 Strut Drive Strut Drive
2 Shaft Exposed Shaft Exposed
3 Shaft not exposed Shaft not Exposed
4 In Aperture In Aperture

If there is no propeller in the water while racing, this shall be recorded as "No propeller".


Each propeller type and installation requires a specific set of measurements. It should be noted, however, that the IMS Editor software contains predefined strut drive measurements for different standard production models, which require only the height of the strut drive and the distance from the keel trailing edge to be recorded. However, basic measurement tools allow propellers to be measured in only about 20 minutes.

15 Prop SHAFT zg ap 01 Shaft installation propeller measurement
15 Prop Strut Drive zg ap 01 Strut Drive installation
15 Prop Shaft Not Exposed zg ap 01 Shaft not exposed
15 Prop In Aperture zg ap 01 In Aperture

A complete definitions of individual measurements is given in Part D of the International Measurement System -IMS Rule book.