Cook Strait statistics: width, depth, ferries, cancellations and swimmers

Cook Strait is about 22.5 kilometres (14 miles) across, the distance New Zealand’s official histories give for the swim crossing between the North and South Islands¹². Guinness World Records describes the channel as 23 kilometres (14.3 miles) wide in its swim records⁷.

The strait joins the Tasman Sea and the Pacific Ocean. Its Māori name appears as Te Moana o Raukawakawa on Interislander’s journey guide⁴, and as Te Moana-o-Raukawa in Guinness World Records’ listing⁷. The ferry route is more than four times longer than the strait is wide, because it starts in Wellington Harbour and winds through Kura Te Au (Tory Channel) and the Marlborough Sounds to Picton⁴.

The Interislander crossing between Wellington and Picton is 96 kilometres (52 nautical miles) and takes about three and a half hours⁴. About two-thirds of the trip is spent in Wellington Harbour and the channels of the Marlborough Sounds, and the remaining third in the open strait. The halfway point comes about 1 hour 40 minutes into the sailing in either direction. The average speed over the whole route is about 27 kilometres per hour (17 mph), or about 15 knots.

Two companies run the crossing: KiwiRail’s Interislander and Bluebridge, which also carries cars, campervans and motorhomes⁸.

To skip the crossing on a South Island campervan or motorhome trip, fly into Christchurch and start with campervan hire in Christchurch. If you hire in the North Island instead, check that your rental company’s terms allow its vehicle on the ferry before you book a sailing.

KiwiRail delivered 99% of advertised Interislander sailings in the year to 30 June 2026 (excluding weather cancellations), up from 98% the year before⁵.

Reliability has recovered from a low of 79% in the year to June 2022¹². KiwiRail’s 2023 report says it brought in a stronger maintenance programme after unexpected disruptions on the Kaitaki, and reliability has risen every year since. In the year to June 2025, non-weather cancellations fell by 40% on the year before⁹.

Across all its train and ferry services, KiwiRail cancelled 564 services because of weather in the year to June 2025, about 7% of all its cancellations⁹.

Sailings and passengers per sailing

The Interislander ran about 2,600 sailings a year with two ships in 2025–26, down from 3,374 in the year to June 2024 with three⁵¹⁰. By our calculation, each sailing still carried about 182 passengers on average in 2025–26, close to the 184 of 2023–24, because fewer ships ran fuller: KiwiRail says utilisation rose from 73% to 83%⁵.

Two identical rail-enabled ferries, each 200 metres (656 feet) long and 28 metres (92 feet) wide with room for 1,530 passengers, are due to enter service on Cook Strait in 2029, according to Crown company Ferry Holdings (July 2026)⁶. They are being built in China by Guangzhou Shipyard International, construction of the first ship is scheduled to begin in May 2027, and the programme runs within a government-approved NZ$1.704 billion funding envelope, excluding NZ$220 million of delivery-partner contributions.

By our calculation, the two new ships will carry 3,060 passengers between them, 97% more than the 1,550 of today’s Kaitaki and Kaiārahi. Ferry Holdings describes the gain as 63% more passenger space⁶.

The HVDC Inter-Island link carries electricity under Cook Strait between the South and North Islands. It was commissioned in 1965 with 570 kilometres (354 miles) of overhead line and three submarine cables across 40 kilometres (25 miles) of the strait, according to Transpower (2024)¹⁴.

A 1991 upgrade added three new submarine cables; the original cables were all retired by 1996, and a second upgrade in 2013 gave today’s northward capacity of 1,200 megawatts¹⁴. In March 2024 Transpower said it was preparing to replace the cables by 2032.