Converting An Icebreaker From An Oil Lubricated Stern Tube Bearing System To A Seawater Lubricated Stern Tube Bearing Considering Environmental And Operating Costs

Operational discharges of oil from the stern tube is a common occurrence for ice breakers as propellers are prone to impact from ice causing shafts to flex and seals are unable to maintain a complete barrier to keep seawater out or lubricating oil in the stern tube. Whereas solar radiation generally speeds the break-down of contaminants, the reduced level of sunlight in the Arctic lengthens the degradation process and increases the likelihood that toxic substances in the stern tube lubricating oil will find their way into the food chain. Hence, deemed “biodegradable” lubricants may not be as biodegradable in the Arctic operating environments. However, there exists a proven, viable option for vessels operating in the Arctic to eliminate stern tube oil pollution. This paper outlines the process for converting the sterntube bearings from oil-lubricated white-metal bearings to Thordon COMPAC seawater lubricated bearings, based on recent works on a twin screw ice breaker at a shipyard in Canada.