Whirling (lateral, transverse, bending) vibration of a typical marine power transmission system is not usually dangerous for a shaft line. Nevertheless, the shaft line lateral vibration analysis is quite often performed, especially for a long, elastic shaft line or when a ship hull is elastic compared to the propulsion system (Camisetti 1982). Whirling vibrations are transferred to the ship hull through journal bearings and may be a source of excessive superstructure vibrations. During whirling vibrations analysis, some parameters have to be checked. Usually, a beam model of the power transmission system is isolated from the ship hull. Therefore, determining the correctness of the boundary conditions is one of the most important, difficult, and debated tasks. In the author's opinion, stiffness and damping characteristics of the journal bearings' oil film, ship hull, and bearings frame should be taken into account (Murawski 2001). Additionally, the influence of the gyroscopic force and thrust force on whirling vibrations is discussed. The presented numerical analysis method is compared and verified by measurements on real ships.