The Transport Accident Investigation Commission (TAIC) has just released an interim report into the incident, which found the Kaitaki's engines failed after one of the ship's safety-critical rubber expansion joints ruptured and prevented the engines restarting.
The chief investigator of accidents, Naveen Kozhuppakalam said the joint which failed had been manufactured in 2005 before being installed in 2018.
However, the manufacturer's advice was the joint should be no older than eight months when installed, inspected annually and replaced every five years.
"This happened because KiwiRail had not followed the manufacturer's advice; even under KiwiRail's own system, the REJ was two months overdue for replacement. Since the incident, KiwiRail has updated its guidance for REJs, but it still doesn't comply with the manufacturer's guidance and doesn't account for the date of manufacture."
The commission has sent an industry-wide urgent warning that all vessel operators using the rubber joints take into account the date of their manufacture to ensure they are fit for purpose.
KiwiRail had yet to supply sufficient evidence that it had taken note of the joint's manufacture date, Kozhuppakalam said.
'Our ships are safe' - KiwiRail
KiwiRail chief executive Peter Reidy has apologised for any distress caused to passengers and crew, and claimed the Interislander has taken "a number of steps to ensure it never happens again".
"Safety is Interislander's top priority. I am proud of how our crew responded, in an extremely stressful situation and in line with all our training, to keep passengers safe and get the ship back to port as quickly as possible.
"Since the incident we've inspected all rubber joints across the entire fleet and replaced all safety-critical rubber expansion joints on Kaitaki and the rest of the fleet, as a precautionary measure."
"Our current regime for inspecting and replacing rubber expansion joints exceeds manufacturers' guidelines, and TAIC's recommendations, and has been audited by international class authorities and Maritime NZ.
"We inspect the joints more frequently than TAIC recommends in its report, and replace them within four years of service use, rather than five years as TAIC suggests.
"TAIC's recommendations will be worked through with Maritime NZ and industry and we look forward to being part of that process.
"In the meantime, we are confident we can demonstrate we are now complying with the advice of our rubber expansion joint manufacturers for our safety critical systems."
The company had carried out an audit of all critical equipment and taken additional steps, including more regular lay-ups, where ships were taken out of service for maintenance, and commissioning international maritime experts to review critical systems, equipment and components on all ferries.
"Interislander's entire asset management regime has now been updated, including more detailed tracking and more frequent inspections of safety critical equipment - including the rubber joints."
"Our message to passengers, staff and customers is clear: Our ships are safe and we are closely monitoring all the safety critical equipment on our vessels," Reidy said.
TAIC's inquiry into the Kaitaki incident is continuing, with current lines of inquiry that include maintenance, safety systems, emergency response and emergency capability.
A final report, setting out findings, safety issues and recommendations, if any, will be issued at the completion of this inquiry.
