The upgrade of the Cook Strait ferry Aratere has faced delays and is now costing $11 million more than planned.
The ship has been at a Singapore shipyard since late April and had new bow added and its hull lengthened by 30 metres.
Owner KiwiRail says the Aratere needed a new power management system, which had not been anticipated and the cost of the refit has risen to $53 million.
The ferry was due back by 1 September, in time for the Rugby World Cup, but KiwiRail says it will not return for at least another two weeks.
Chief executive Jim Quinn does not think any blame lies with the Singapore shipyard for the delays in the project, and says he is pleased with the quality of its work.
But he says the company is embarrassed the project has not gone as planned, and will review it to determine the reason.
Mr Quinn is confident the other ferries can cope with Rugby World Cup demand until the Aratere sails again.
Wellington's tourism body, Positively Wellington Tourism, is also confident the ferry services will cope with demand.
