The Cook Strait ferry Aratere is due back in Wellington on Friday after a five-month upgrade in Singapore.
The ferry was supposed to be back in time for the start of the Rugby World Cup, but delays to the upgrade have made it three weeks late.
Improvements include a new bow and propellors, as well as 30 metres added to its length.
Ferry owners KiwiRail says it had hoped the ferry would arrive sooner but are glad it will be back for their busiest shipping time in October.
The company has coped with the Aratere's absence during the past three weeks by chartering another ship to help with freight services.