Environmental Friendly Ship Propulsion System: Case of Aft Stern Tube Bearing

Environmental protection is finally an important issue and, due to previous sea contaminations and for economic reasons, merchant fleets are paying more attention to materials selection and to ship design. Taking into consideration that the propulsion system lubrication, whether oil or water, and the consequent lubricant leakage into sea is a critical problem, the present study examines the practicability and the benefits of implementing water lubricated polymer stern tube bearings instead of conventional white metal bearings lubricated by oil. The investigation method is related to a numerical model and a software application based on finite difference method and isoviscous model. Results, based upon data collected from two different types of actual vessels in service, have shown that power loss in polymer bearings is at least 6 times less than in conventional white metal ones indicating that polymer journal bearings are more energy efficient and environmental friendly.