Transport Accident Investigation Commission chief commissioner David Clarke and chief investigator of accidents Naveen Kozhuppakalam spoke to media about the agency's interim report, released today, on the grounding of the Cook Strait ferry in June this year.
The Aratere ran aground shortly after departing Picton at 9.45pm on 21 June - prompting inquiries from the transport agency, Maritime New Zealand and TAIC.
None of the 47 passengers and crew aboard were injured and the ship was refloated just under 24 hours later.
TAIC's report drew evidence from the ship's voyage data recorder, the steering control system and interviews with crew.
It confirms details RNZ reported from leaked documents in July that a crew member had triggered the auto pilot into the wrong course before it crashed into the shore.
The TAIC report showed that a new Kongsberg steering system had been installed on the Aratere just weeks prior in May, and 83 inter-island crossings were made in the three subsequent weeks.
On June 21 alongside the day and night master, an additional experienced master was onboard re-familiarising themselves with the ship, and was pilot instead of the night master.
Also present was an officer of the watch, a lookout and a helmsman.
Kozhuppakalam said the Aratere was just past its second waypoint off Mabel Island when the autopilot was engaged at 2126:01, putting steering for the ferry under autopilot control.
"At 2126:30, the re-familiarisation master pressed the turn execute button, intending to initiate the Mabel Island waypoint turn.
"The Aratere had passed Mabel Island 36 seconds earlier, so pressing 'execute' told the ship's autopilot to make the turn for The Snout headland waypoint, rightward onto a course of 73.8°, which this early in the voyage was towards land."
He said around 31 seconds after the 'execute' command, the night master saw Aratere was heading towards shore and called the helmsman back to the central steering console.
"In turns, the Helmsman, the officer of the watch and the night master pressed the 'takeover' button and turned the wheel hard to port, all to no effect. Aratere continued its turn toward the coast."
He said the bridge team were unaware that to transfer steering control from the autopilot to the central steering console, the new steering system required them to either set the same rudder command at both consoles, or hold down a takeover button for five seconds.
At 2127:43, with Aratere heading towards shore at 13 knots and helmsman lacking steering control, the night master put both engines at full astern.
It took 21 seconds for the port propeller and 38 seconds for the starboard propeller to begin turning astern.
At 2128:06 the manual steering mode was engaged.
By 2128:34, Aratere had slowed to about 7 knots at the 10-metre sounding, then slower, and by 2128:50 it had grounded.
Following the grounding, the ferry's hull remained watertight, but the ship did sustain damage to the internal structure of the bulbous bow that had to be repaired.
The Commission will issue a final report on completion of its investigation.
KiwiRail response
KiwiRail operates the three Interislander ferries - the Aratere, Kaiarahi and Kaitaki.
In a statement, Interislander executive general manager Duncan Roy said the company was implementing improvements in the wake of the Aratere grounding.
"The safety of our customers, the public and our people is paramount. Our response to this incident reflects our commitment to learning from it and doing better."
After the grounding, Interislander worked with Kongsberg - which provided the new steering system - to understand what had happened.
"Having identified the cause of the event, we issued new guidance on the use of the autopilot system and upgraded re-training of deck staff on the control system. This was followed by a full competency test and updated direction on best practice use.
"We are continuing to implement recommended actions based on lessons we have learned in our own investigation. We are focused on training, change management and bridge management, and are continuing to work with Kongsberg."
