Thrust Deduction in Contrarotating Propellers

Abstract : A theoretical method is presented for calculating the steady propulsive interaction (thrust deduction) force in contrarotating propellers. Contrarotating propellers operating at off-design loading and spacing as well as the contribution of a rudder were investigated. The importance of the separate thrust deduction of the forward and aft propellers in analyzing the behavior of a CR propeller set was shown. Numerical results are given for a MARAD high- speed containership. Some principal findings for the subject ship are: good agreement between theory and experiment with regard to the thrust deduction of a centerline rudder, at equal thrust the forward and aft propellers produced 73 percent and 27 percent of the total thrust deduction, respectively, and the total thrust deduction is reduced by unbalancing the propelling thrust with smaller thrust carried on the forward propeller.