The Achilles Bulker anchored off Mount Maunganui in 2023. Photo / Alex Cairns
Poor welding led to a cargo ship’s rudder breaking off as the vessel left Tauranga Harbour, an investigation has found.
Only the swift actions of the crew stopped the 177m, fully loaded Achilles Bulker from grounding as they halted it with just 1m of water under the keel.
The 2023 close call came just over a decade after the 2011 Rena grounding off Tauranga’s coast caused New Zealand’s worst maritime environmental disaster.
An investigative report by the Transport Accident Investigation Commission (TAIC) has been released explaining how the Achilles Bulker’s 14.2-tonne rudder came to detach on July 24, 2023.
The report said the weather was calm as the Panama-flagged ship finished loading logs at the Port of Tauranga, and began pre-departure preparations about 2pm.
Two Port of Tauranga pilots - one qualified and one trainee - were aboard.
With the ship’s master, they agreed the trainee would have “the conn”, or conduct of the ship, for the outbound sailing, with support from the qualified pilot.
It was the trainee’s first time taking charge since joining the pilot training programme about five months earlier.
By 3.17pm, the China-bound ship had begun its voyage with the assistance of two tugs.
At 3.28pm, shortly after clearing the Tauranga Harbour entrance, the ship’s heading began to swing off course.
The bridge team was taking corrective action to return the ship to the centre line in the shipping channel when a loud bang was heard throughout the ship, and the ship shuddered about 3.49pm.
The qualified pilot took over the conn and continued trying to get the ship back on course.
A second, louder bang was heard a minute after the first.
As the ship continued out of the channel into shallow waters, the qualified pilot took steps to slow it, including ordering the crew to drop both anchors.
By 3.56pm the ship had “effectively stopped” outside the channel.
It “narrowly” avoided grounding, the report said, with only about “1m under-keel clearance”.
“It is virtually certain that the swift and well-co-ordinated actions of the pilots and ship’s crew prevented the ship running aground.”
Escort tugs towed the ship further offshore where the vessel could be anchored.
It stayed there, about 6.5km off the coast surrounded by a 50m exclusion zone, for several days until it was brought back to the port to await a tow for repairs overseas, according to reporting at the time.
The investigation report said it was not immediately apparent to the crew during the incident that the rudder had broken off.
That was revealed by a diver’s survey the next day, along with fractures to other parts of the rudder system.
After an extensive search led by the Port of Tauranga, the rudder was recovered from the channel on July 26.
An inspection found the pintle was missing from the bottom of the rudder.
The pintle is a metal pin the rudder pivots around. The pintle was 942mm tall and weighed 428kg. The rudder weighed 14,231kg (14.2 tonnes).
The investigation found that, during dry dock maintenance in China in 2021, the pintle assembly had been removed and reinstalled for the first time in the 20-year-old ship’s history.
Wreckage examination and testing found inconsistent welding penetration and thickness securing the pintle, 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.”
It meant components securing the pintle in place failed and the pintle was lost before the ship lost its rudder.
Other components of the rudder system were exposed to excessive forces, ultimately leading to the loss of the rudder and loss of control of the ship.
“It is virtually certain that the way the rudder pintle assembly was reinstalled did not ensure that the pintle would remain in place during normal shipboard operations.”
The commission said ships with a similar pintle arrangement to the Achilles Bulker were at “far greater risk”, putting seafarers and the environment in “significant danger”.
Since the investigation, the commission has identified the safety issue relating to the quality assurance and oversight used during the pintle reinstallation and made recommendations to address it.
Maritime New Zealand agreed to work with an international marine accident forum to investigate building an evidential base for action to improve quality assurance systems related to dry dock work, which would include installation, major repairs and maintenance of ship systems.