Equipment Class 3, even if you operate as 'Class 2'

The vessel was set up according to their class-approved FMEA in a ‘DP 2 configuration’ with open bus ties, four of the six generators running online, and equally split across two bus sections.

The FPSO they were due to attend had a holdback Tug connected to allow more control during operations.

The vessel was 100 m from the FPSO and approaching when a failure alarm was initiated for Main Engine 1. This rapidly escalated to losing the port switchboard followed by the starboard switchboard almost simultaneously.

In its blacked-out condition, the vessel proceeded to drift away from the asset due to the correct procedures being followed and being set up in a drift-off position.

The vessels Bridge department immediately contacted the FPSO to warn of the emergency, and the FPSO lowered the starboard side Yokohama’s in case of impact between the vessels.

The anchors and towing lines were prepared as the engine department proceeded to fault find and regain power to the vessel. The Tug was called to disconnect from the FPSO and standby for towing, if necessary.

The engineers discovered water in the fuel system, within the settling and service tanks on both port and starboard sides. and were required to drain the water from both systems. After two hours, the engines were finally restarted, and the vessel returned under control, having lost 2nm position.

Figure 4 – Simplified example fuel system

Investigation of the event uncovered a few areas to consider:

• The water ingress to the FO overflow Tank was traced back to the FO overflow tank vent pipework.
  
  
• The FO overflow tank vent pipe was traced and found to pass through a water ballast tank, which at the time was full.
  
  
• Upon emptying the water ballast tank, the leaking stopped, and when the vent pipe was safely inspected, it was found with several holes from years of corrosion.
  
  
• The FO overflow tank was set up to the port and starboard settling tanks simultaneously.
  
  
• FO operation procedures were reviewed, and concluded that there was room for improvement in regard to the storage, transfer and treatment onboard.
  
  
• During the incident, both port and starboard FO purifiers were operating; however, no alarms were activated.
  
  
• An investigation of purifier settings revealed that the water monitoring function was inactive in a factory setting. The Purifier controller was still in default factory settings, which did not match the vessel's separator type onboard. The controller settings were updated per the manufacturer's instructions to match the actual purifiers onboard. All functions and alarms, including water content alarm, were verified.