Oil lubricated shaft seals contributing to ocean pollution

Oil lubricated shaft seals contributing to ocean pollution
Rope tangled on propeller and propeller shaft

Oil lubricated shaft seals counterproductive to environmental legislation, says Thordon Bearings. 

Thordon Bearings has found more than 100 references to “propeller shaft seal failure and oil leakage into the sea”, resulting in ocean pollution that is overlooked and needs to be addressed quickly.

“Regular reports in the maritime technical press and indeed from hull repair specialists themselves show with alarming frequency that the aft seals of oil-lubricated shaft lines are damaged by either ropes or fishing nets and wholly responsible for this source of pollution,” said Craig Carter, Thordon Bearing’s director of marketing and customer service.

One recent report highlighted work to a general cargo ship with a “leaking stern tube assembly”, while another reported repairs to the damaged seals of a semi-submersible offshore platform in Mexico. Yet another reported repairs to a ship leaking oil in Antwerp, after fishing nets had become entwined around the seal assembly.

“It’s all good business for underwater ship repair companies, of course, but these problematic shaft seals, which account for 43 per cent of all shaftline failures, are not only impacting the marine environment but also the shipowner’s bottom line,” said Mr Carter.

Based on its calculations, Thordon Bearings says that every vessel that operates an oil-lubricated propeller shaft system configured with an aft seal, could be leaking on average 6 litres (1.6 U.S gallons) per day – a statistic backed up by research carried out by New York-based Environmental Research Consulting, which found 240 million litres of operational oil is leaked annually from ships.

Terry McGowan, president and CEO, Thordon Bearings, said: “While the list of vessels that have polluted the oceans following damage to sterntube seals is extensive, it is only a fraction of the number of incidents taking place. The only certainty we have is that the amount of oil discharged into the marine environment from faulty or damaged seals is of significant environmental concern and should be addressed immediately by Administrations and regulators. And this doesn’t even include normal leakage from worn seals.”

Based on the potential impact of this level of oil pollution in its marine environment, the US EPA recommended that “all newbuild vessel operators endeavour to use seawater-based systems for their sterntube lubrication in order to eliminate the discharge of oil from these interfaces to the aquatic environment”. The EPA has included this clause in its Vessel General Permit rules (sect. 2.2.9) since 2013.

“The maritime industry’s continued use of these systems is counterproductive to the excellent work it is doing to clean up our seas with, for example, the introduction of mandatory legislation to reduce emissions, prohibit oily water discharges or prevent the spread of alien aquatic species. We now need regulations to stem the flow of oil leaking from a ship’s propeller shaft,” said Mr Carter.