Impact of lateral ship propeller loads in ice-covered waters on the contact conditions of stern tube bearings

Abstract Increasing ship traffic in the polar regions leads to more frequent collisions between ship propellers and sea ice which causes extreme lateral propeller loads. These loads lead to mixed friction in the aft journal bearings of the propeller shaft which causes bearing wear and thus potentially results in a failure of the entire propulsion system. The influence of the propeller-ice collision on the lateral propeller loads is unknown. These loads are, however, required to determine the resulting contact conditions in the bearings. Thus, this study presents a method to determine full-scale propeller-ice contact loads using small-scale ice-milling tests. Data of the vessel SA Agulhas II is used as case. The method includes the deviation of dimensionless parameters to transfer small-scale to full-scale data using the Buckingham‑Π method. The ice-milling tests deliver propeller torques and lateral propeller loads as result. The propeller torque was compared to full-scale torque measurements from the ship in ice to identify and validate the scaling method. The validated lateral propeller force was used to calculate the aft bearing contact conditions using simulation. The scaling method presented in this work firstly allows the determination of full-scale radial propeller forces and propeller torque on the basis of small-scale ice-milling tests. The deviation of the dimensionless torque parameter is 12.8% comparing small-scale ice-milling test results with full-scale measurements on the ship in ice. With this result the proposed scaling method is validated. The full-scale radial propeller force resulting from the scaling method, leads to a severe mixed-friction regime in the aft bearing ( p a,max = 86.41 MPa, h min = 0.22 µm & Λ = 0.2) which underlines the criticality of propeller-ice contact regarding bearing wear.