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Abstract: This paper describes two procedures for the calculation of thrust and torque coefficients of a tandem propeller. Both procedures are based on a Combined Method, which consists of a Vortex Lattice calculation combined with an extended Goldstein approach. The first procedure performs individual calculations for the two propellers. To account for the interaction of the two propellers the consecutive calculations are linked. Since the linked procedure includes some simplifications it can be used only for calculations in homogeneous inflow. To perform calculations in inhomogeneous inflow or account for additional effects the second procedure is implemented, which carries out the combined calculation for the whole tandem propeller. This allows the direct calculation of the propellers’ influence on each other. The results of the two procedures are compared to measured data from open water tests.