New DNV GL Notations for Water-lubricated Tail Shafts

Two new tail shaft monitoring class notations from DNV GL offer ship owners and operators the possibility of unlimited intervals between tail shaft withdrawal surveys for water-lubricated systems. With these two voluntary class notations, TMON (closed loop water) and TMON (open loop water), DNV GL becomes the first classification society to use a condition-monitoring based survey process that eliminates the requirement for tail shaft withdrawal surveys at predetermined intervals. 

The new notations, which cover the design and follow up monitoring, are based on a condition monitoring system which predominantly uses a remote sensor to measure stern tube bearing wear each time the propeller shaft stops turning. This allows the crew to monitor the condition of the bearings. The condition monitoring system also gives owners and operators the ability to optimally plan maintenance, avoiding unnecessary tail shaft withdrawals, while having a system in place to identify any deterioration in condition early on.   

“This is a real milestone for our customers,” said Tuva Kristine Flagstad-Andersen, Head of the DNV GL Machinery and Systems Section. “Water-lubricated tail shaft systems have become increasing popular as the regulatory pressure to reduce environmental impacts has grown. These new notations mean that there is no requirement to undertake a tail shaft withdrawal survey, as long as the results from the condition monitoring based survey do not reveal unacceptable deterioration in the condition of the tail shaft, bearings or lubricant system.”