NEW ZEALAND’s Transport Accident Investigation Commission has found aspects of the interaction between old and new steering systems were unknown to the bridge team of the Interisland line rail/ro-pax Aratere when it ran aground leaving Picton on 21 June.

In its Final Interim Factual Report TAIC finds that having identified the need to replace Aratere’s steering control system due to the scarcity of spare parts for the 26-yo original equipment, a new Kongsberg system was installed and commissioned during the vessel’s wet-docking in May 2024.

This had involved replacing the controls at each of the command consoles except for the autopilot, which was part of the original track pilot integrated bridge navigation system by a different manufacturer; the new Kongsberg steering control system was integrated with the track pilot. Aratere subsequently completed 83 Cook Strait crossings without incident.

Aratere departed Picton at 2119 on 21 June on a regular sailing to Wellington, with the regular night master on the bridge as well as another experienced master who was re-familiarising himself with Aratere. The re-familiarisation master was operating the engine controls from the port bridge wing, supervised by the night master. The helmsman was steering the ship using the central wheel.

Abeam of the first waypoint, Mabel Island, the autopilot was engaged in course mode. However, in course mode the track pilot will not automatically begin the turn. The pilot must push the ‘execute’ button, upon which the track pilot will apply the required rudder to take the ship around the programmed arc onto the next course. In actuality the execute button was pushed after the waypoint had been already passed, meaning the autopilot had moved on to the next sector, and began to turn Aratere to starboard.

Those on the bridge registered the problem but could not overrule the system as they were not aware of either the need to align the rudder commands between consoles nor how to activate the force takeover feature.  The night master was able to slow the ship from 13 knots to 7, before it ran aground at approximately 4 knots in Titoki Bay. It was refloated, with relatively minor damage, 48 hours later.

TAIC says it is is continuing to collate and verify evidence directly related to the grounding and is pursuing several lines of inquiry of a systemic nature.