Harbourmaster doubts Cook Strait ferry breakdown caused by bad weather

Wellington's harbourmaster says he'll be very surprised if weather caused the breakdown of a Cook Strait ferry on Saturday night.

It drifted dangerously close to the rocky south coast of Wellington.

Two new ferries are set to replace Interislander's ageing fleet from 2025 but for now, the remaining two ferries, the Aratere and the Kaiarahi, will be working overtime to pick up the slack.

Harbourmaster Grant Nalder said by the time the Kaitaki put down its anchors on Saturday evening, it was 0.6 nautical miles from water shallow enough to ground it.

"They issued a mayday call," he said. "You do a mayday if there's risk to life, so the captain felt it was serious."

A timeline released by Maritime New Zealand showed the ship first reported engine problems just before 5pm.

It dropped its anchors and a mayday call was made at 5.05pm.

It was just over a nautical mile - about 2km - off Sinclair Head, better known as Red Rocks.

There was a south-westerly wind of 30 to 40 knots, and swells up to a metre high.

Nalder said that was nothing the ferry hadn't seen before. "That's rough, it's not extreme, and it's not at the vessel's operating limits."

Passengers on board told RNZ the same - it was rough, but not terrible.

The weather did, however, push the ship closer to danger, Nalder said.

"If it had been a northerly instead of a southerly they would have just been quietly drifting out to sea, which may be a bit upsetting for the passengers, but absolutely safe for the ship until they get it going.

"It was just because they were getting carried towards the shore that this became an issue."

Maritime New Zealand incident controller Paul Craven said police, ambulance and the defence force were assembled, and five rescue helicopters put on standby.

Six boats were sent out for support - fellow Interislander ferry the Aratere, police boat Lady Elizabeth, two harbour tugs, a pilot boat and a fishing vessel.

The crew on board managed to restore power around 7pm, and the Kaitaki was able to get itself into the harbour under its own steam.

It docked about 9pm - seven hours after leaving Picton.

KiwiRail general manager for Interislander Walter Rushbrook told Morning Report the breakdown was rare for the normally reliable ferry.

"This is an extremely rare occurrence for Kaitaki, it's one of our key workhorses and it's been very reliable for us."

Investigations had been launched by Interislander itself, as well as by the Transport Accident Investigation Commission (TAIC), and Maritime New Zealand.

Extra sailings had been scheduled for the other ferries and the Kaitaki wouldn't be leaving the harbour until the fault was fixed.

Transport Minister Michael Wood told Nine to Noon that, at 30 years old, the Interislander ferries were requiring more maintenance.

"The Interislander ferry fleet is coming towards the end of its life, and that's well known," he said. "That has meant there has been a decline in the reliability of the vessels.

"We've had extensive maintenance work under way on all the vessels to keep them as safe and reliable as possible, so it's concerning that we have had this incident."

Help was on the way. Building consent had recently been granted for the new terminal at Kaiwharawhara, designed to accommodate two new, larger, hybrid-electric ferries.

However, with these not expected to arrive before 2025, the Kaiarahi, Kaitaki, and Aratere will have to hold on for a little bit longer.