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 (2/3 blades) Folding (2/3 blades) e.g. Gori Feathering (2/3 blades) e.g. MaxProp

If propeller does not meet requirements for any of these three types or if there is no any propeller in the water while racing, this shall be recorded as "No propeller".


Propeller installation types


Strut drive Shaft exposed Shaft not exposed In Aperture



For each propeller type and installation there is a set of measurements that has to be taken. However, in the IMS Editor software there are pre-defined strut drive measurements for different standard production models where only height of the strut drive and the distance from the keel trailing edge needs to be recorded. Regardless, propeller measurements take only about 20 minutes with basic measurement tools.


Shaft installation propeller measurement


Strut drive installation measurment

In aperture drive installation measurement

  A complete definitons of individual measurements is given in Part D of the IMS Rule book.

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