Classification societies are changing their monitoring rules for seawater-lubricated propeller shafts in line with the rules governing the inspection and withdrawal of oil-lubricated stern tube systems.

China Classification Society (CCS) announced in July that if certain condition monitoring criteria are met, shaft withdrawal for inspection might be extended to 15 years.

The rule change follows recent revisions by Lloyd’s Register and Bureau Veritas, which published amended SCM and MON-SHAFT rules in January 2013 and January 2014, respectively. DNV GL, the world’s largest classification society, with a registered fleet of 266.9mgt, is expected to publish new rules in 2016.

“Changes to classification society rules represent a significant breakthrough for manufacturers of water-lubricated shaft bearing systems,” said Andy Edwards, Commercial Director of market leader Thordon Bearings.

“A major stumbling block to the wider take-up of the more environmentally efficient seawater-lubricated system has been the requirement to withdraw the shaft for inspection every five years. So the changes are very welcome as they are more representative of the advancements made in polymer bearing technologies and corrosion-resistant shaft coating systems.

“We expect the revision will be highly welcomed by those shipowners looking to comply with the stringent U.S. Environmental Protection Agency vessel general permit (VGP) regulations, which are now in force to impose strict limits on operational oil discharges for vessels operating in US coastal waters and the Great Lakes,” Edwards added.