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The design of an interior permanent magnet (IPM) machine, in particular, its pole and slot combination, determines the nature of its magnetic forces, which influences not only the torque but also acoustic noise and vibration characteristics. Vibrations can shorten bearing life and are an especially important parameter in marine applications, which have strict regulations such as on electromagnetic compatibility. In this study, two-dimensional(2D) finite element analysis (FEA) was used to model magnetic vibration sources in two 100-kW marine fractional-slot IPM machines with different pole and slot combinations (8 pole-12 slot and 10 pole-12 slot). The magnetic forces were calculated according to rotor position, current phase angle, and load. The results are validated by experiments.