A MODIFICATION error in the starboard exciter unit led to the Norwegian Star (IMO 9195157) incident in February last year, the Australian Transport Safety Bureau has concluded.
The cruise ship lost power and was left bobbing around the waters off Cape Liptrap, Victoria, before being towed back to Melbourne by tugs.
The ship had been on its way to Dunedin in New Zealand.
According to the Bureau, the ship was powered entirely through its starboard propulsion unit, the port unit being under repair from an earlier failure on January 24.
The starboard unit had itself failed on December 11, 2016, before being repaired.
“The configuration of the (starboard) 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,” the ATSB reported.
“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.”
According to the Bureau, the failure of the unit in its original configuration and the subsequent failure of the original port exciter unit on 24 January were both probably due to a breakdown in electrical insulation.
The Bureau said the ship operator’s decision to sail from Melbourne with only the starboard propulsion unit breached no regulatory requirement and was based on confidence in the repaired starboard unit.
The ATSB has issued recommendations to ship operator Norwegian Cruise Line Holdings and the equipment manufacturer ABB Industry Oy to review processes for monitoring the condition of brushless exciter units in Azipod installations.
“Operation of newly designed equipment without redundancy increases operational risks,” the ATSB reported.
“Equipment manufacturers and ship operators must apply extra diligence when designing, installing and operating modified equipment, especially safety critical equipment.”