A Cook Strait passenger ferry hit a rock, denting its hull, when its rudder was turned the wrong way, an inquiry has found.

The Strait Shipping ferry Monte Stello was able to continue on to Picton unaided and no one was harmed during the May 4, 2011, incident.

The Transport Accident Investigation Commission report said while making the left-hand turn into Tory Channel, the ferry's rudder was inadvertently placed in the wrong direction, causing the ship to deviate from the planned track.

"The error was soon realised and corrective action taken, but not soon enough to prevent the ship glancing off a rock on the northern side of the channel."


The ship's hull was dented but there was no puncture and one of its two rudders were damaged but it was able to continue on its journey.

The commission found the error in rudder direction was not picked up in sufficient time to prevent the grounding because the procedures for checking and cross-checking every action during critical phases of navigation, known as bridge resource management, were not being strictly followed by the bridge team.

It recommended to KiwiRail, the parent company of Interislander, to ensure a standard operating procedure was fully understood and followed by all crews, all of the time