Cargo ship within 1m of grounding after rudder broke near Tauranga

Poor welding led to the rudder of a 177m cargo ship breaking off as it left Tauranga in 2023, with only the swift action of the crew preventing it from running aground, an investigation has found.

A report by the Transport Accident Investigation Commission (TAIC) into the incident was released today which explained how the 14.2 tonne rudder of the Achilles Bulker detached on July 24, 2023.

The Panama-flagged ship bound for China finished loading logs at the Port of Tauranga and began pre-departure preparations at about 2pm.

Two pilots — one qualified and one trainee — from the Port of Tauranga had boarded the ship.

It was agreed the trainee pilot would have the conduct of the ship, known as the conn, for the sailing with support from the qualified pilot.

Shortly after it cleared the harbour entrance, the ship's heading began to swing to port and deviate from its intended track.

Corrective action was being taken by the bridge team to return it to the centre line of the shipping channel when a loud bang was heard throughout the ship at 3.49pm.

The qualified pilot took over the conn and a second, louder, bang was heard seconds later.

Steps were taken to slow the ship as it continued out of the channel and into shallow waters, including ordering both anchors to be dropped.

By 3.56pm, the ship had "effectively stopped" outside the channel with around 1m of water under the keel, narrowly avoiding grounding.

"It is virtually certain that the swift and well-co-ordinated actions of the pilots and ship’s crew prevented the ship running aground," the report found.

Escort tugs then towed the ship further offshore to be anchored, where it remained for several days before being brought back to port to await a tow for overseas repairs.

The rudder was recovered from the shipping channel on July 26, with an inspection finding that the pintle — a metal pin the rudder pivotted around — was missing.

The investigation found the pintle assembly had been removed and reinstalled during dry dock maintenance in China in 2021.

Examination and testing of the wreckage found inconsistent welding penetration and thickness, with the welds having "significant porosity".

"Those welds were susceptible to cracking from normal vibrations as they were generally poor quality with limited weld penetration."

This meant components that secured the pintle in place failed, allowing the pintle to drop out before the rudder broke off.

"It is virtually certain that the way the rudder pintle assembly was installed did not ensure that the pintle would remain in place during normal shipboard operations."

The Transport Accident Investigation Commission said ships with a similar pintle assembly were at "far greater risk".

Since the investigation, the commission had identified the safety issue relating to the quality assurance and oversight used during the pintle reinstallation and made recommendations.

Maritime NZ agreed to work with an international marine accident forum on the issue.