Thordon Bearings has welcomed the introduction of a new classification society notation, allowing extended inspection periods for propeller shafts using seawater-lubricated bearings.
DNV GL has established a new voluntary TMON notation for open-loop water lubricated propeller shafts, which follows similar rule revisions by Lloyd’s Register (LR), Bureau Veritas (BV) and the China Classification Society (CCS). The new rule stipulates that propeller shafts operating water-lubricated bearings no longer need to be withdrawn for inspection every five years.
The previous five-year shaft inspection rules stated that most shaft condition monitoring notations were a major deterrent to the wider take-up of the water lubricated system. However, now DNV GL has revised its rules, Thordon Bearings can provide an alternative to oil-lubricated propeller shafts.
The condition-monitoring-based survey process, which waives the requirement for the withdrawal of the tail-shaft at pre-determined intervals, also enables ship operators to consider seawater lubricated systems as a compatible alternative to meeting US Environmental Protection Agency’s Vessel General Permit [VGP] requirements.
DNV GL recommended in the latest edition of its Technical and Regulatory News bulletin that ship owners consider the condition-based notation for water-lubricated tail-shafts at their next dry-docking.
Craig Carter, Thordon Bearings’ Head of Marketing and Customer Service, commented: “This is a major breakthrough for fleet-wide conversion back to the environmentally and operationally more efficient water-lubricated propeller shaft bearing. Like LR, CSS and BV’s recently revised shaft condition monitoring rules, DNV GL’s new TMON notations are indicative of the significant advancements made in polymer technology and the ability of these seawater-lubricated bearing systems to prevent further environmental damage from operational oil leakage.”
