A vessel's main diesel engine stopped during voyage, remaining inoperable for a period of approximately an hour. Fortunately the vessel was in open sea and no damage occurred to the ship.

Extent of damage
The fuel oil flow to the main engine had been blocked by a flow meter which had stopped. Small impurities in the fuel oil may cause seizure of rotating parts in flow meters of the positive displacement type, resulting in a sudden and complete stop of the fuel oil supply. The same may also happen due to mechanical failure of the drive mechanism of the flow counter. Flow meters are normally fitted with an integral strainer/filter, which in case of clogging may cause a gradual reduction of the fuel oil flow.

In one typical fuel oil arrangement the flow meter is fitted on the suction side of the fuel oil booster pump. In another arrangement the flow meter is fitted on the pressure side of the booster pump. Over the years DNV has been informed of stoppage both of propulsion diesel engines and diesel generators due to blockage of fuel supply caused by flow meters.

Lessons to be learned
Flow meters of positive displacement type should be regularly monitored during operation. Further, the fuel oil flow arrangement should be designed so that blocking/stopping of the flow meter does not cut the fuel supply to the diesel engines. This can be achieved, for example, by fitting a bypass differential pressure valve across the flow meter.