Autopilot Malfunction Led to Grounding
The Australian Transport Safety Bureau (ATSB) has released its investigation report into the grounding of the landing craft Lauren Hansen, off Melville Island, in the Northern Territory, on April 11, 2018 citing an autopilot malfunction.
As the ship left Darwin, the ship's master found that the autopilot malfunctioned repeatedly by applying port rudder regardless of the set heading. The master steered the ship manually until they had departed port limits then attempted to engage the autopilot again with limited success. Shortly after departing port limits, the Lauren Hansen encountered engine difficulties with the fault traced to the starboard main engine’s gearbox cooling system. The ship’s crew dropped anchor to the south-west of the Vernon Islands while the gearbox cooling system fault was rectified.
The ship’s master proceeded with the passage plan, which passed close to land off Melville Island. The next morning, the ship made another unexpected turn to port without any alarms or indications, turning closer to land. Shortly after, the chief mate noticed that the ship had started to turn to port. He reduced power on both main engines and attempted to call the master using the bridge telephone. Failing to receive a response using the telephone, the chief mate then left the bridge and went down to the master’s cabin, one deck below. He alerted the master to the situation and both then returned to the bridge. As the master and chief mate entered the bridge, they noticed that the ship no longer appeared to be turning but had steadied on a north-westerly heading. At about the same time, the Lauren Hansen grounded on a shoal about 170 meters off the shoreline on Cape Keith, Melville Island.
The Lauren Hansen was re-floated with the tide. The ship’s tanks and bilges were sounded and with no breaches or water ingress evident, and she commenced passage back towards Darwin. An underwater inspection back in port identified several areas of impact damage across the ship’s bow with the largest indentation about 143cm long, 50cm wide and about 8cm deep. While all the damaged areas had sustained hull distortion and indentations, no cracks, fractures or tears in the hull were evident.
The ATSB found that it is likely the turn to port was due to an intermittent fault with the autopilot or compass top sensor unit. “The incident demonstrates that any known problem with a ship’s control system, such as the autopilot, needs to be carefully assessed before committing the ship to sea. It also demonstrates the need to consider measures, such as changes to the passage plan, to reduce the risk involved in sailing with a potentially unreliable control system.”