Friction-induced vibration in marine shafts caused by water-lubricated bearings

Rubber stern tube bearings are critical to marine propulsion systems; however, friction-induced vibration may arise under conditions of low rotational speed, high load, localized heating, and inadequate lubrication. To characterize the dynamic behavior of the bearing–shaft system, a series of controlled experiments was conducted by varying the load pressure, thermal conditions, and rotational speed. Time- and frequency-domain responses, together with shaft orbit measurements, were analyzed to identify friction-related signatures. The results indicate that time-domain responses exhibit pulse-like features, while the spectra contain pronounced components at the fundamental and higher-order harmonic frequencies. Concurrently, the shaft orbits deviate from regular elliptical trajectories, exhibiting irregular geometries with angular distortions. The consistent features observed across the temporal, spectral, and orbital domains provide complementary indicators of friction-induced vibration. These findings demonstrate the potential of multi-domain response analysis for diagnosing friction-related anomalies in marine bearings.