Defect in ferry never pinpointed

The steering on the Cook Strait ferry Aratere broke down twice in February. Picture / Mark Mitchell

Steering gear on the Cook Strait ferry Aratere failed twice in February - but the quick actions of captain and crew kept the vessel from becoming a shipping hazard, a Transport Accident Commission investigation has found.

However, owing to a lack of information about equipment in the vessel, the "intermittent fault" was never identified and may still exist.

In both incidents, navigation of the vessel was continued safely using the starboard steering gear and rudder, and neither the safety of the ship nor its occupants was compromised.

In the first incident, on February 9, just inside Wellington Harbour, the helmsman told the master he was having difficulty maintaining the course.

The master thought the port rudder had stuck and eventually decided to stop the vessel to investigate the fault before proceeding. Engineers were unable to identify any fault.

Later analysis of voyage data showed the port rudder had stopped working from a point outside the harbour entrance but the helmsman had probably assumed the ship was being affected by tidal currents.

"Had the master not taken the ship out of the main shipping route, the Aratere may have become a significant hazard for the fast ferry closing from astern," the report found.

In the second incident, on February 20, the master noticed the port rudder was malfunctioning again, and decided to anchor in Queen Charlotte Sound.

An electrician could not identify the problem but after cleaning electrical contacts the fault appeared to be fixed.

The commission found the fault was an intermittent one, so it may still exist or it may have been accidentally fixed while fault-finding.

"The problem was that the documentation did not accurately reflect the installed equipment of the Aratere, so fault-finding is a process of educated guesses," the report said. Technicians were forced to work by a process of "elimination".

Since the incident, Toll NZ has replaced various parts.

- NZPA