A dropped propeller will mean 60,000 fewer passengers will make the journey across the Cook Strait on an Interislander ferry during the busy months of summer.
The Aratere ferry was taken out of service after its propeller shaft was extensively damaged and a propeller fell off during a sailing last week.
Interislander closed its bookings to shuffle passengers onto its two other ferries, which will take over services for the peak months of December and January.
On Thursday, Interislander's state-funded owner KiwiRail revealed the service cost of losing the Aratere ferry for those months - a 45 per cent decrease in freight and passenger capacity.
KiwiRail said 60,000 fewer passengers would be able to travel with Interislander between the North and South Islands.
"We originally forecast to carry approximately 200,000 passengers and 55,000 cars during December and January," Interislander general manager Thomas Davis said.
"We now expect to carry only 140,000 passengers and 33,000 vehicles without an additional ship."
The Aratere is expected to be out of action for at least six months as parts are imported and repairs undertaken.
An alternative ferry will be brought in to handle the load, however it is not expected to be ready until mid-January.
Freight services have also been affected.
Interislander will only be taking new bookings for foot passengers until the Aratere or a replacement ferry is in service.
Existing bookings for vehicles will be honoured.
The propeller hasn't yet been found despite searches by KiwiRail and an investigation is looking into why it broke off.
The $106m Spanish-built Aratere entered service in 1999 and was quickly dubbed "El Lemon" by crew after problems started developing.