Recently published information describes an arrangement consisting of a small set of vanes attached to the rotating hub of the propeller. These vanes are located aft of the propeller and rotate with the propeller. The small vanes are designed to reduce the swirl placed in the slipstream by the action of the propeller. It is reported that the strength of the hub vortex is reduced with this arrangement. The result provides a propeller of higher efficiency. This efficiency gain has been recorded with a relatively large number of ships fitted with this device. The enclosed presents data and analysis evaluating the validity of the claims.

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