On the Design and Use of Contra-Rotating Propellers in High-Speed Craft

Abstract

This paper describes first a design method for contra-rotating propellers using the momentum theory to determine the mutually induced velocities. Approximate formulae for these velocities have been worked out allowing both the design and the performance analysis of contra-rotating propellers. This is achieved by separating the treatment of a set of propellers into two independent ones with corrections on the intake velocities and on the speed of rotation of the aft propeller. A practical application of a contra-rotating propeller in a highspeed power boat is then discussed. It turned out that this propulsion device is economically beneficial if used together with a stern-drive unit. Smaller propeller, diameter, better cavitation characteristics, smaller vibration level and absence of a heeling moment also contribute to the benefits of a contrarotating propeller as a propulsion system for high-speed craft.