Interislander ferry Kaitaki returns to service on Saturday following maintenance in Singapore.

KiwiRail said the work was necessary to ensure the safety, reliability and performance of the ship until the arrival of new ferries in 2029.

Chief operations officer Duncan Roy said it was done during winter to minimise impact on passengers and freight customers, while ensuring the ships were ready for a busy summer ahead.

The return of Kaitaki will see Interislander resume a two-ship timetable.

Kaitaki's Wellington to Picton morning sailing will depart at 8.30am instead of 8.45am, while the return Picton to Wellington sailing will depart at 2pm instead of 2.15pm.

The timetable adjustment was designed to support more reliable operations and improve connections with the Coastal Pacific train.

"We're looking forward to welcoming passengers on board and helping connect people with friends, family and holiday destinations across Aotearoa,” Mr Roy said.

Customers were advised to book early for school holidays, Christmas and New Year sailings.