Interislander's Aratere ferry returned to Wellington on Friday after a five-month upgrade in Singapore.
The ferry was supposed to arrive back at the start of September, but delays to the upgrade made it three weeks late.
The upgrade increases Aratere's capacity by 100% for passengers, and 30% for freight, trucks and cars.
Interislander general manager Thomas Davis says the upgrade was an effective answer to their need for more capacity.
The ferry is due back in service late next week.