A guide to crossing Cook Strait: what it’s really like to cross one of the ‘most dangerous’ bodies of water and how operators decide if it’s too choppy


As quartermaster on ferries crossing Cook StraitMick Williams remembers the times when waves crashed over the bow of a ferry as the ship crashed into the water.

But those days were rare, Williams said. “Chances are you’ll have a good trip.”

He noted that he was speaking from the perspective of a sailor, who had worked on ships around the world, so his perception may be different from that of someone who has spent little time on the water.

People knew conditions in Cook Strait could change quickly, he said, and that’s part of why the body of water had an undeserved bad reputation.

* Inter-island ferries cancelled, wild weather continues
* Safety is paramount after the Wahine disaster
* Ferry passengers endure a ‘roller coaster’ ride on the Cook Strait in a 7-meter high swell

Waves crashed overboard during a 2017 Cook Strait ferry crossing.


Waves crashed overboard during a 2017 Cook Strait ferry crossing.

“I don’t want to dramatize. I love it, it’s a nice stretch of water,” Williams said.

“I certainly wouldn’t stop anyone from crossing the Cook Strait, but you pick your time,” he said. “It’s beautiful on a beautiful day.”

Large waves and high winds cause the cancellation of some Cook Strait ferry crossings, and Wednesday MetService warned of a risk of heavy swell until Thursday evening along the coast of Porirua and Kāpiti.

From time to time, the advancing crossings cause a bit of a stir.

A Cook Strait ferry heading for Picton on a stormy day in July 2017


A Cook Strait ferry heading for Picton on a stormy day in July 2017

For instance, Kaiarahi ferry passengers in winter 2017 reported that they were almost out of vomit bags. Those on board who regularly crossed the strait said it was the worst sailing they had experienced. Interislander subsequently canceled sailings due to deteriorating weather conditions which had caused a 7m swell.

On Wednesday, Interislander executive managing director Walter Rushbrook said guidelines for deciding whether to call off a sailing include a wave height of 5m for passenger crossings and 5.5m for cargo crossings.

A ferry captain had absolute authority to cancel crossings at lower heights if he felt it was warranted, Rushbrook said.

“These standards ensure both the comfort of our passengers and the safety of the freight we carry on board our ferries.”

Big waves on Wellington's south coast.  (file photo)


Big waves on Wellington’s south coast. (file photo)

Williams said he remembers times when no one could stand still on deck. “In my case, you cling to the steering wheel. I was also trying to steer the ship through the weather,” he said.

He was unsure of the height of the biggest swells he had encountered in the strait, but said they were “pretty high”.

“The bow goes straight up in the air and then it comes back down and hits the water. It’s quite powerful.

On a reassuring note, Williams said the ferries had enough personnel on board to deal with the worst-case scenario, and the crew members were experienced sailors.

He pointed out that around half of the journey from Wellington to Picton was also in the calmer waters of the Marlborough Sounds and Wellington Harbour.

The entrance to Wellington Harbor (file photo)


The entrance to Wellington Harbor (file photo)

Even on a calm day there was a bit of a swell at the entrance to Wellington Harbor and the ship was starting to move. “There will be some kind of swell and then the ship will go through it on its own,” Williams said.

Navigating through the Sounds entrance required concentration. “At the entrance, all tides meet”, although it was not something passengers would notice.

“I never get tired of crossing the Marlborough Sounds. You always see something different,” he said.

Williams said it was not uncommon for a passenger to fall ill even on a calm crossing, but it was rare. Even under more normal conditions, it was unusual for anyone to get sick.


The April 15, 2020 swell on Wellington’s south coast damaged homes.

On its website, Interislander said strong northerly winds were generally nothing to worry about. The water would remain calm, but the outside decks could be closed.

“However, a strong southerly wind, said to be from the south, can cause significant swells,” the company said.

“Our Interislander Cook Strait ferries have outriggers, which help keep our vessels stable in moderate swells. But there will be days when we will be sailing in choppy seas that are a little uncomfortable for some.

“There are also times when we delay or cancel departures when it is too dangerous to leave.”

Passengers could postpone their trip to a day with better weather conditions. Depending on the type of fare, they might do it for free or might have to pay a fee.

A Niwa study said the Cook Strait was known for a high frequency of strong winds.

“Northerly winds occur more frequently, but are generally not associated with high waves in the strait,” the study said.

The Kaitaki ferry arriving at Picton


The Kaitaki ferry arriving at Picton

High waves did affect the strait when the winds came from the south, due to the relatively open exposure to that direction.

A Niwa report on Wellington’s climate said that in an average year Baring Head – on the south coast of the North Island near the entrance to Wellington Harbor – had 255 gusty days winds greater than 63 km/h and 72 with gusts greater than 96 km/h.

The Cook Strait acted like a “giant wind tunnel,” according to the Niwa report. This was because it was the only space between the mountainous North and South Islands, and located within the westerly wind belt known as the Roaring Forties.

“The swell over the Cook Strait can increase rapidly with a storm from the south, sometimes reaching heights of 15m or more.

“Due to wind funneling and strong tidal currents, Cook Strait is considered one of the most dangerous and unpredictable bodies of water in the world.”


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