Torsional systems of marine propulsions are simulated by multiple inertias connected by linear springs and linear viscous absolute- and relative damping values. Absolute damping is acting between a global system without rotation and the rotating inertias of engine, propeller and auxiliary drive. Relative damping is acting in between inertias. Inertia and torsional stiffness is predicted by calculation and can easily be verified by measurements. Damping values are roughly estimated by various empirical methods. The measured vibratory stress of an intermediate shaft allows different damping identifications. Discrepancies in damping models for engines and propellers currently used will be presented. General numerical problems of various identifications will be shown as well.
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