The Cook Strait ferry Aratere is out of service due to radar and stabiliser issues.
KiwiRail spokesperson Sophie Lee said both the ship's radars failed last week, and a starboard stabiliser problem is also being looked at.
A technician flown into the country to fix the problems arrived on Tuesday.
Ms Lee said passenger services have not been affected as the Arahura has picked up the sailings, and at this stage the ferry will be back on the water on Wednesday.
Last week the Kaitaki hit the wharf in Picton, damaging berthing equipment.