The DP equipment class 2 vessel was operating within a windfarm safety zone, with all thrusters operational, three of the six diesel generators running and the bus-tie breakers closed. At the time the vessel was in operating in close proximity to wind turbines and was engaged in gangway operations. The environmental conditions were fair at the time of the incident, with 1m wave, 10kts wind and 1.5kts real current. 

Whilst connected to a turbine, an alarm was generated on the DP operator station, ‘Unbalanced load on SWBD 1’. The DPO informed the Gangway Operator to immediately stop all transfers over the gangway, whilst the investigation was carried out. 

In the engine room, diesel generator 3 had tripped. The minimum number of generators was set to three, therefore the next standby generator automatically started and synchronised within 50 seconds, restoring generating capacity to switchboard 1. 

Following communication from the duty engineer confirming the reason for the tripped engine, and the restoration to minimum number of allowable generators within the safety zone, as prescribed by the Master’s Orders, the DPO gave the green light for gangway transfer operations to resume. 

On investigation, the following was found: 

A similar event has occurred previously on a fleet vessel. Though not identical scenarios, the loss of a diesel generator occurred on a sister vessel after its fuel filter was also not correctly bled of air following maintenance. 

These events occurred only one month apart on two vessels within the same fleet. The first event was reported to shore management and the lessons learnt shared internally within the company, so how and why did it repeat the following month on a sister vessel? 

The act of changing/cleaning filters is a task which comes up regularly within every vessels preventative maintenance system, so could it be that this is a highly common event occurring worldwide? It highlights the importance of preventive maintenance, not only that it is carried out in due time, but that even errors occur on seemingly easy tasks. It reiterates the importance of not carrying out maintenance on ‘on-line’ equipment when operating within the safety zones.