A date appears to have been set for Interislander to get new, bigger Cook Strait ferries – but it seems nobody told the ferry operator.

With passenger and freight expected to increase significantly in coming years, the ground-based work needed to accommodate the larger ferries has been outlined in a report to Greater Wellington Regional Council's regional strategy committee.

At least one operator – Interislander – planned "to purchase and operate new larger vessels on the Cook Strait. These are scheduled to arrive in 2022," the council report said.

"These new vessels will require new terminal facilities as well as additional infrastructure."

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But according to Interislander's overseer KiwiRail, the process was not so far down the track.

It was only "looking at upgrading its ferries" and was still working through options, a spokeswoman said.

No timeline was set and no decisions had been made, she said.

KEVIN STENT/STUFF Aratere had a $54m overhaul in 2011 but is now nearing the end of its life.

Acting KiwiRail chief executive Todd Moyle said in October that all three of its ferries – Aratere, Kaiarahi, and Kaitaki – were nearing the end of their lives.

KiwiRail needed new ships "built for our specifications and requirements", he wrote in a Stuff opinion piece.

"Our future freight and tourism needs will require bigger ships, and our ports at Wellington and Picton need to be able to handle them."

One of the decisions still to be made was whether to have a train deck, which would allow a loaded train to roll on at the start of a journey and roll off at the other end, or whether to just transfer cargo from trains to trailers.

DEREK FLYNN/STUFF The Kaiarahi Interislander Ferry - now nearing the end of its life - recently had a refit in Singapore.

"In the next couple of months the results of our investigations and consultation with our people, our union partners, customers and stakeholders will be known," Moyle said.

"The size and number of ships in our new fleet, and the type best suited to our future freight and tourism needs, will be decided. Whatever the result, new ships will deliver more capacity, increased resilience, better fuel efficiency and greater reliability for our customers."

The new ferries would have new facilities and would make for a better crossing.

"Once the decision is made we will embark on the next stage of our future fleet programme – building the new ships that will continue to unite New Zealand across that most tempestuous of barriers, Cook Strait."

Cook Strait ferry Kaitaki, which is also nearing the end of its life.

Greater Wellington is also leading a project to develop a new "multi-user" Cook Strait ferry terminal in Wellington, which will serve as the port for both Interislander and Bluebridge ferries.

The two sites being considered at Interislander's current Kaiwharawhara site and Kings Wharf, near the existing Bluebridge operation and Wellington Railway Station.

"Forecasts of future demand indicate that substantial growth in both freight and passenger numbers is likely over the next 10-20 years," the report said.

"However, the terminal infrastructure is a long-term investment, and so an understanding of demand over a 50-year timeframe should be considered when designing. By 2025 it is expected that annual passenger numbers will rise to 1.7 million."

Passenger numbers were about 1 million in 2010.

COOK STRAIT FERRIES: A HISTORY

* 1875: A passenger service between Wellington and Picton begins with a weekly service till 1962 when the last ship in service, Tamahine, was withdrawn.

* 1962: The first roll-on, roll-off ferry, Aramoana, enters service.

* 1983: New ferry Arahura arrives, while the Aramoana and Aranui were laid up two years later.

* 1994: Christchurch businessman Brooke McKenzie starts the Sea Shuttle fast ferry. It lasts the summer.

* 1995: The North by South Straitrunner starts a Paremata to Picton service but the company goes into receivership in May 1996.

* 1998: Mana Seacat starts a Paremata to Picton service in its Te Hukatai catamaran but the firm folds five months later.

* 1999: Fast Cat Ferries begins its short-lived TopCat service. It winds up in November 2000.

* 2005: The last Lynx service sails from Picton.

* 2011: Aratere refurbished for nearly $54 million, and its hull was lengthened by 30 metres. But that was followed by multiple issues including, in 2013, when it lost a propeller in Tory Channel

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