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In marine propulsion systems with direct-coupled two-stroke large diesel engines, the angular position of the propeller with respect to the crankshaft remains unchanged during the whole operation of the engine. The interference between major harmonic orders of the engine torque is avoided by choosing a number of blades, different from any divisor of the cylinder number. However, interferences between other harmonic orders of the engine torque and the major harmonic order of the propeller torque -which is equal to the number of blades- may increase the amplitude of torsional vibrations. The paper shows that there is an optimum Phasing between crankshaft and propeller for which a decrease, up to 20%, of the dynamic shear stress of the shafting -in comparison with the worst possible phasing- may be achieved. This results points out the importance of being able to calculate, in the design stage, the best phasing of engine and propeller

Among the excitation sources of vibration for the marine propeller shafting, the propeller itself plays a significant role. It is the main source of excitation for the axial vibrations and a major contributor among the excitation sources for torsional vibrations. Thus, the possibility to predict the harmonic structure of the torque and thrust, in the design stage of the propeller system has a great importance for the designer. In this direction, the paper presents an analytical method of calculation for the propeller torque and thrust based only on the propeller series diagrams and general empirical formula for the wake and suction coefficients. A vortex model of the marine propeller, based on Prandtl lifting-line theory, has been developed. Considering the system of bounded and free vortices representing the propeller blade and its interaction with the incipient wake generated by hull motion, the velocity field around the blade profile is determined.