Magnetic Compass Fails the Autopilot Resulting in Grounding

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Summary

On 10 April 2018, the 45.5 m landing craft Lauren Hansen was preparing for sea at Hudson’s Creek, Darwin, Northern Territory. The ship’s operator, Shorebarge, had chartered the ship for a voyage to Elcho Island.

As the ship exited the Darwin Harbour, the master encountered difficulties using the autopilot, which when engaged, applied port rudder regardless of the heading order set on the control panel.

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.”

Findings

These findings should not be read as apportioning blame or liability to any particular organisation or individual.

  • The decision to execute the planned route, which passed close to land, rather than a route in more open waters similar to the chart’s recommended track through the Van Diemen Gulf, increased the risk of a grounding particularly when the unreliability of the autopilot was a known factor.
  • Lauren Hansen experienced an unexpected turn to port while on passage in autopilot steering mode. The ship’s manual or emergency steering modes were not engaged or utilised and the ship subsequently grounded.
  • The unexpected turn to port was most likely the result of an intermittent fault in the ship’s autopilot unit or in the compass top sensor unit that fed heading information to the autopilot unit.
  • There was no compass deviation book maintained on board Lauren Hansenas required by Australian Maritime Safety Authority regulations.

Recommendations

ATSB noted that relevant organisations may proactively initiate safety action in order to reduce their safety risk. For this reason, Shorebarge, the ship’s operator, will take the following safety actions:

Repairs and replacement

The autopilot unit and compass top sensor were both replaced with new units, with the autopilot now reported to be functioning normally. The ship has since been dry-docked and repairs and replacement of the damaged hull areas have been carried out as recommended by class.

Magnetic compass adjustment

Lauren Hansen’s magnetic compass was inspected by a qualified compass adjustor and an up-dated table of deviations compiled. The compass was found to have been operating satisfactorily with deviations on all headings less than 5º.

Shipboard safety meetings

Safety meetings were conducted on board Shorebarge vessels to review the grounding and to discuss the management of fatigue. The discussion included a review of AMSA’s legislative requirements and the company’s procedures for fatigue management.

Safety message

AMSA stated the following:

This incident showed the implications of a failure or malfunction of any aspect of the ship’s steering systems and that these should be carefully assessed before committing a vessel to sea. If necessary, the situation should be rectified or measures implemented to reduce risk before the vessel embarks on a voyage.

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Source: ATSB

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