Influence of Propeller-Ice Loads on the Wear Development in Stern Tube Bearings of Marine Propulsion Systems and Identification of Critical Operating Conditions

Abstract Increasing ship traffic in ice-covered waters leads to more frequent collisions between ship propellers and sea ice which causes extreme impulse loads on the propeller. Theses loads are transferred through the propeller shaft to the sliding bearings of the stern tube, especially, the aft stern tube bearings. Extreme bearing loads can lead to mixed-friction regimes which cause wear in the bearings and eventually results in a failure of the entire propulsion system. The effect of ice-induced loads on the contact conditions in the sliding bearings is widely unknown. Thus, a study of the influence of these loads on the contact conditions and wear behavior in stern tube bearings resulting from observed sea ice conditions and operating conditions of the ship is necessary. This paper aims to investigate the influence of ice collision loads on the contact conditions in the bearings of the stern tube of the research vessel SA Agulhas II. For this purpose, an elastohydrodynamic simulation and a multibody simulation based on field measurements were performed. As a result, this paper identifies the operating condition thresholds (i.e. propeller torque and rotational speed) during propeller-ice collisions that cause mixed-friction conditions in the bearings. On the basis of these conditions, a risk map is generated to assess the actual wear risk by including the frequency of occurrence of the corresponding mixed-friction condition over the duration of a voyage.