Comments from the report:
An AVR problem in diesel generator No. 1 engine caused an over voltage in the system. Due to increased voltage, the standby machine could not be brought online, and the switchboard required a controlled blackout. After this, many alarms from Network B were observed due to the supply being interrupted. An hour later, there was a total loss of network communication affecting many field stations together with loss of DP communication to all thrusters, which caused the vessel to drift off. The probable cause was accidentally resetting network A, when trouble shooting of network B was taking place.
Further investigation of the overvoltage issue found a 3-phase breaker was faulty to engine No.1; the breaker was replaced by an onboard spare. The DP system manufacturer concluded that the vessel was operational as designed, indicating a possible human mistake by rebooting network A.
Considerations of the IMCA Marine DP Committee from the above event:
The vessel instigated a DP yellow alert whilst a fault was investigated. Considering the weather conditions and nature of investigation the vessel should have either abandoned operations or been fully prepared to do so.
Given the circumstances, it is evident the vessel returned to normal operations too quickly and whilst reinstatement of the system was still in progress. The root cause of the incident was not given in the report, but it is evident that work involving the resetting of the network caused the loss of DP communication with the thrusters and subsequent position excursion. While total network failure and subsequent drift off represents a DP incident, the initial failure of the AVR only represents an undesired event.