Oil discharges from a ship’s propeller shaft system are an issue for commercial ship owners. A 2010 study by a New York Consulting firm estimated the total worldwide amount of lubricants from operational discharges from ships would be about 130 to 244 million litres annually. To add perspective, oil pollution from the Exxon Valdez tanker spill in 1989 was 41.6 million litres. Most ships use mineral oil to lubricate the propeller shaft and the oil is contained in the propeller shaftline by the aft seal – which is the oil to sea interface. According to the new U.S. Environment Protection Agency Vessel General Permit (VGP), all vessels built on or after Dec. 19, 2013 and trading in US waters must use an environmentally acceptable lubricant (EAL) in all oil to sea interfaces before their next drydocking. This paper will review: the renaissance of seawater based systems, a general description of a seawater lubricated bearing system, current commercial ship users and results, lower operating costs with “free” seawater and no aft seal, conversions of existing ships and resistance of shipyards to change standard designs from oil to seawater. The paper will also review new Classification rules from LR, CCS and BV for seawater lubricated propeller shaft systems, allowing the shaft to remain in place if monitoring conditions are met - which removes a major obstacle that ship owners had with seawater-based propeller shaft bearing systems.

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