Increased propulsion efficiency, less fuel consumption, increased maneuverability etc. are some of the major eye catching properties in a ship to study contra-rotating propeller system over single screw propeller system in spite of the former's relatively high initial and operational cost. In the present study, for a particular loading condition, a comparison of efficiency between the contra-rotating propeller system and single screw propeller system is made and for the contra-rotating propeller system a comparison between the two efficiency calculation procedures (Circulation Theory and blade element theory) is made. For this reason a procedure is developed basically to calculate the self and mutual induced velocities of the fore and aft propeller of the contra-rotating propeller system. The lifting line theory is applied for the calculation of velocity field. For the calculation of the induced velocities the Circulation Theory of Propeller action is used. According to Circulation Theory the propeller can be modeled by three types of vortex system and then Biot-Savart law is applied to calculate the induced velocities. The interaction effects of the two propellers are determined with regard of slipstream. No effects due to the passing of the blades of forward and aft propellers are included. Radial distribution of the self and mutually induced velocities are calculated on the lifting line in such a way that each propeller is handled like a single propeller. Then the Efficiencies at different sections of the propeller are calculated both for the Blade Element Theory and Circulation Theory. And calculation of individual efficiency both for the fore and aft propeller is determined from the Bp-δ chart.
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