The Power Electronics Research group at Aberdeen University is working towards providing a complete time domain model of an electrical drive for marine applications. Effects such as vibration, shaft and propeller induced oscillations and noise in ships due to the use of cycloconverters will be studied in this way. This thesis therefore reports the investigation of machine vibrations resulting from electromagnetic forces. The machines of primary interest are ac induction machines, but much of the work reported in this thesis has broader significance. To assess the vibration problems of propulsion motors, the exciting force and the vibration behaviour of the motor must be modelled. The investigation has therefore been carried out in five principal areas. The development and use of a new time domain magnetic force model. The development of a method to calculate machine stator natural frequencies. A laboratory investigation of system parameters of both a stator and also an entire motor, which draws important conclusions not previously reported. A machine vibration prediction method based on analysis of interactions between the magnetic forces and the motor system parameters. Vibration measurements on a machine to provide data for correlation with predicted results. The Saber simulator has been used throughout to develop the force calculation model. The force model is used to calculate the time and space dependent magnetic force wave, in particular, when the motor is loaded and fed from a nonsinusoidal converter, which makes this model particularly useful for machine vibration calculations. The computer model can be readily used with previously developed cycloconverter models to achieve a complete cycloconverter propulsion simulation.