Calls are growing for an independent inquiry after a litany of problems have befallen the Cook Strait ferries, disrupting freight movement worth at least $14 billion annually and leaving passengers stranded.
The Cook Strait was becoming "the biggest pothole on State Highway 1", opposition transport spokesperson Simeon Brown said on Thursday, following a week during which Interislander and Bluebridge were hobbled by multiple problems.
Parliamentary questions from August show that 93 percent of Interislander ferries were on time in the 2018 financial year, but this was down to 68 percent in 2022.
Meanwhile, 99 percent of Interislander ferries ran in 2018 versus 79 percent in the last financial year.
A 2021 business case for the Interislander to get two new purpose built ferries - the first of which arrives in 2025 - shows the KiwiRail-owned line makes 3800 crossings on an average year, taking about 850,000 passengers, 250,000 cars, and $14 billion of freight.
The true Cook Strait crossing value, with Bluebridge in good times adding two ferries to Interislander's four, will push those figures much higher.
KiwiRail describes its Interislander service as an "extension" of State Highway 1 and the main trunk railway line.
But Interislander's Kaitaki has been freight only after it lost power in Cook Strait in late January, and the Kaiarahi had an engineering issue on Monday and needed repairs, leaving a period where the Aratere was the only Interislander ferry taking passengers.
Interislander executive general manager Walter Rushbrook on Thursday said the Kaiarahi and Aratere were back taking passengers and freight.
The Valentine would sail "as possible and when necessary" but was constrained by crew numbers.
Meanwhile, privately run Bluebridge this week had an engine problem on the Connemara meaning its services from Thursday until Sunday were cancelled, and there was a warning of no available space on other sailings.
Bluebridge's Straitsman was boarding, already delayed, on Friday when a staff member was injured after an incident with a truck.
Maritime NZ briefly ordered the ship to remain in port while it investigated, then released it late on Friday morning.
The same ferry was earlier this week forced to stop for a period due to "urgent operational requirements".
Its other ferry, the Strait Feronia, is currently in dry dock.
The government has previously blamed problems on "previous governments" for not investing in ferries.
They are claims refuted by Brown, who said it was only in recent years that reliability had dropped.
It was time to consider an independent review into ongoing issues which, on top of freight problems, had seen people stranded in both islands, unable to rebook, and some having to fly across the Cook Strait and leave their car on the wrong side, he said.
Public Transport Users Association national coordinator John Reeves called for a full independent inquiry into Interislander and Bluebridge to see why ferries kept breaking down.
"Interislander and Bluebridge are failing people. It is a massive inconvenience and should never have happened," he said.
He blamed the issues on the privatisation of Interislander ferries by National in the 1990s. It returned to government ownership in 2008.
"If something goes really bad there will definitely be a royal commission," he said.
Transport Minister Michael Wood's office sent a statement saying he was meeting with the KiwiRail board on Thursday evening "for assurance on their next steps".
He did not comment on calls for an inquiry.
On top of the government funding of $430 million for two new ferries plus infrastructure, the government was investing $30m to improve coastal shipping, he said.
* This story originally appeared on Stuff.