The Transport Accident Investigation Committee’s report into the loss of the Interislander ferry Aratere’s propeller in 2013 makes valuable recommendations around the standard for advanced propeller manufacture, says KiwiRail group general manager Todd Moyle.
He says having tighter manufacturing tolerances for large fixed pitch propellers – like those used on the Aratere – was an important step in ferry safety and a key recommendation in the report.
“We agree with TAIC’s finding that the fracture which caused the propeller to come off was the result of bending forces. Our own extensive investigation, led by the international engineering consultancy firm Aurecon, concluded the likely cause of those forces was an irregularity in the propeller blade due to the manufacturing process used.
“However we do not accept TAIC’s view that KiwiRail did not follow the manufacturer’s advice on the best way to fit the propellers and that if we had, some of the conditions that contributed to the shaft’s failure would have been less likely to have happened.”
Moyle says the proposed method of fitting the propellers was impractical because of the very long shaft fitted, and the method used to fit the propellers was discussed with the manufacturer, who accepted it as an alternative.
KiwiRail had accepted TAIC’s recommendation on document management practices and record keeping around the fitting process, and implemented the recommended change by ensuring significant modifications follow project management office procedures.
“I should also emphasise that during this incident the ship was always under control and at no point were passengers or the vessel at any risk. This was not a safety issue. It had 95% reliability in the last financial year. The Aratere is a real workhorse for New Zealand,” says Moyle.
He went on to say that the Aratere is the hardest working of the Interislander ferries. Already this year it had completed more than 1200 Strait crossings, carried more than 15,000 trucks and 54,000 cars, along with 180,000 passengers and more than one million gross tonnes of rail freight, despite being in Singapore for more than two months for its regular survey.
All Interislander ferries and facilities are fully operational for the peak Christmas season after the disruption caused by the Kaikoura earthquake.