Avoiding the slippery slope to lubricant pollution

30 Oct 2011
Installing Thordon's seawater lubricated propeller shaft bearing replacing metal bearing and oil

Installing Thordon's seawater lubricated propeller shaft bearing replacing metal bearing and oil

Environmental lobby groups are pressing the shipping industry, and its regulators, to move away from traditional oil-based lubricants which are causing significant harm to the global marine environment.

Recently, the environmental protection organisations WWF and Friends of the Earth International (FOEI) submitted a hard-hitting paper to the IMO’s Marine Environment Protection Committee (MEPC). This raised serious concerns about the extent of oil-based lubricant pollution and the need for changes to both IMO regulations and industry operating practices to reduce the adverse impact that the leakage of such lubricants is having on the marine environment.

Marine lubricants are used to lubricate machinery in various areas onboard vessels, including stern tubes and thrusters, and can be discharged into the sea during normal operations, as well as through equipment wear and failure. The mixture of mineral oil base and additives in lubricants results in persistent bio accumulative and toxic chemicals accumulating in the marine environment, particularly in coastal areas, where around 80% of shipping movements occur.

The first authoritative study of the scale of marine lubricant pollution, a report published in 2009 by Environmental Research Consulting, widely known as the Etkin Report, found that between 33,000 and 61,000 tonnes of oil-based lubricants are discharged every year into port and harbour waters alone. This is approximately 1.5 times the amount of oil spilled from the Exxon Valdez.

Specific concerns

WWF and FOEI say they have specific concerns about the discharge of lubricants below the waterline by stern tubes and thrusters, since these are almost impossible for authorities to observe. Introducing monitoring systems and abatement mechanisms for this type of marine pollution would improve detection rates relating to mechanical failure and aid operational efficiency, but further action is needed by the international shipping community to really address this issue.

Some industry sources calculate that the shipping industry used up to 2.8 million tonnes of lubricants in 2009, suggesting that the actual amount of lubricating oil pollution could be even higher than these estimates.

According to Dr Simon Walmsley, marine manager, WWF International, “There are two broad options for a way forward within IMO, both of which would require the support of member states. One would be to deal with this issue as part of ongoing revisions that are being made to MARPOL V. The other is to develop stand-alone guidelines specifically covering lubricant pollution. The latter would take longer to achieve, but may well be the more effective option in the end.”

Options for owners

There are several possible solutions, including the use of biolube products and the adoption of water-lubricated stern tube designs. The latter could have a big impact on stern tube oil seepage, which the Etkin Report estimates to contribute between 12% and 46% of total lubricant pollution in ports and harbours.

“The concerns raised by WWF and FOEI point to a clear need to adopt the technology we have developed in recent years,” says Craig Carter of Thordon Bearings, a Canadian manufacturer of seawater lubricated bearings. “There is a proven alternative to an oil-lubricated sealed system that completely eliminates stern tube oil pollution, and this is an open system that uses seawater as the lubrication medium in place of oil.”

With this approach seawater is piped from the sea through non-metallic shaft bearings and returned to the sea. No stern tube oil is required and the use of non-metallic bearings is now claimed to offer a level of performance that is similar to metal shaft bearings.

There may be a higher initial cost for the stern tube bearing system due to corrosion protection. However, this can be recovered fairly quickly through lower running and service expenses, as demonstrated with bulker, tanker, ferry, cargo and cruise ships operators that use seawater lubricated stern tube bearings.

The Thordon Compac stern tube bearings have been designed to reduce running friction and improve low speed hydrodynamic film development. The lower (loaded) portion of the Compac bearing is smooth and the upper half is designed with water grooves for lubrication and cooling. Although start-up friction is initially higher, at rated shaft speeds the drag on the rotating shaft resulting from the viscosity of the lubricating fluid is lower with water than with oil, thereby resulting in potential fuel savings.

Carter adds: “By using new bearing designs and technologies, shipping companies can now eliminate both operational and accidental stern tube pollution. The WWF and FOEI have done valuable service in highlighting the significant effect this pollution is having on our oceans, but the technology to stop it is already available and proven on more than 2000 ships in service.”

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