The seat for the stop solenoid on the port main engine was damaged causing a slight air leak past it, this acting on the stop cylinder piston caused a reduction in main engine rpm. The reduction in rpm caused a low voltage alarm followed by breaker trip and low frequency alarm. Power was lost to bow thruster No 3 due to a breaker trip on the switchboard, the port azimuth thruster was not affected as the clutch out rpm was not reached.
The vessel has reduced the inspection interval of the stop solenoid valves from annual to six months.
Considerations from the above event:
- The vessel did not appear to reach its worst case failure (WCF) and although DP redundancy was effective precautionary measures were initiated.