Final Report


What happened

On 9 February 2017, the passenger cruise ship Norwegian Star departed Melbourne, Australia, on a scheduled cruise to Dunedin, New Zealand. There were 2,113 passengers and 1,017 crew on board. On departure, the starboard propulsion unit was operational following its recent repair, and the port propulsion unit was under repair following its failure on 24 January. This meant that the ship was operating only with the starboard propulsor.

At about 0134 on 10 February, Norwegian Star was about 22 NM south-west of Cape Liptrap, Victoria, Australia, when the starboard propulsion unit failed. Propulsion could not be restored and tugs were deployed from Melbourne to tow the ship back to Melbourne. The ship arrived back without further incident at about midnight on 11 February.

What the ATSB found

The ATSB found that Norwegian Star lost function of its starboard propulsion as a result of the failure of the recently repaired starboard exciter. The configuration of the exciter unit had been modified as part of its repair, and the unit failed as a result of an error in the design of the modification. Insufficient clearance had been provided to allow for movement and thermal expansion of components during the unit’s operation. This error was not detected during the design, installation and trialling of the modified exciter unit.

The need for the repair of the starboard exciter unit had followed its failure on 11 December 2016. The failure of the unit in its original (as-built) configuration, and the subsequent failure of the original port exciter unit on 24 January, were both probably due to a breakdown in electrical insulation. Processes for the monitoring of exciter unit condition were ineffective in detecting deterioration prior to unit failure.

The ship operator’s decision to sail from Melbourne with only the starboard propulsion unit did not breach any regulatory requirement and was based on confidence in the reliability of the repaired starboard unit. While the repaired exciter was of proven design concept, the detailed design specific to this propulsion system application had not previously been used in-service.

What's been done as a result

The ATSB has issued recommendations to the ship operator Norwegian Cruise Line Holdings and the equipment manufacturer ABB Industry Oy to review the processes for monitoring the condition of brushless exciter units in Azipod installations, considering the mechanism of failure of the port and starboard brushless exciter units on Norwegian Star.

Safety message

Operation of newly designed equipment without redundancy increases operational risks. Equipment manufacturers and ship operators must apply extra diligence when designing, installing and operating modified equipment, especially safety critical equipment.

The passenger cruise ship Norwegian Star

The passenger cruise ship Norwegian Star

The occurrence


Safety analysis


Safety issues and actions

Sources and submissions