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This report describes the measuring system for propeller vibratory force at IHI's towing tank and the computer program which calculates the propeller vibratory force in cavitating conditions. The measuring system has several devices to make the noise level low and analyze a huge amount of measuring data effectively. The bearing force dynamometer of the system has a six-component balance connected to the rotating propeller shaft. Pressure pickups of the semi-conductor type are used to measure the vibratory pressure on a hull. Experimental results for both a full model ship and a thin model ship are shown, where the effects of number of propeller blades are examined. In these cases, even number bladed propellers give rise to a larger thrust and torque variation than odd number bladed propellers. Comparison of the results obtained from the computer program with the series test results that the bearing force can be estimated by the characteristics of nominal wake harmonics. (Wassmann)