You’ve got the ASOG, so now you’ve got to follow it

The unit was operating in open bus configuration with all four thrusters operational and four of the six generators connected, two on either side of the bus.

There had been reports of noise and heavy vibrations coming from a sea water cooling pump, allocated to Thruster No.1, therefore the engineers requested the DPOs to deselect and stop Thruster No.1 from the DP system, so investigations could be carried out. The DPOs agreed to the request, reducing the available thruster capacity on the portside to 50%.

Approximately half an hour later, a blackout on the starboard power system resulted in the loss of Thruster Nos. 2 and 3. 

The DPOs took immediate action and changed over to Manual control, facilitating disconnection of equipment by the crews between the MODU and the platform. The DPOs were able to maintain MODU position on the one remaining thruster, Thruster 4, from the port redundancy group. Starboard side power was restored and Thrusters 2 and 3, were running and accepted back into the DP control system within seven minutes.

The crew were instructed to continue the disconnection and once all end-user equipment was safely removed, the MODU commenced its passage out of the 500m zone. The starboard redundancy group experienced a second blackout whilst transiting out of the safety zone and the MODU was again left with only one thruster to complete the move beyond the 500m zone.

The crew were able to safely transit the MODU to a nearby anchorage where they then undertook further diagnostics and remediation of the failures.

Investigation of the event concluded that:

• The failure of Thruster 1 sea water cooling pump was due to shaft bearing damage.
• Blackout of the starboard power system was due to the malfunction of a running diesel generator control module; this produced an incorrect signal to the AVR and consequently affected both connected diesel generators.
• ASOG had not been adhered to during operation inside 500m zone. Any loss/failures of any DP related equipment should trigger yellow status and all parties should be informed.
• There was poor communication between Bridge, engine room and third-party contractors.
• Any activity related to the operation needs to be approved by the Bridge and cascaded to all personnel onboard.
• Regular checking on engine room needs to be complied at all times. Any unusual or suspicious conditions of machineries or equipment should be informed immediately.