It said operating with one vessel was challenging, particularly during a busy period, but the company has managed it before.
KiwiRail spokesman Taru Sawhney said eight additional sailings of the Kaitaki would be put on, on Sunday and Monday, when the vessel was due for a scheduled layby.
Foot passengers on the cancelled sailings of the Kaiārahi had been accommodated on Kaitaki sailings, mostly on the same day.
Sawhney said around 1300 private vehicles were affected by the Kaiārahi outage and those customers were being offered a full refund, the opportunity to rebook at no additional cost and compensation for reasonable costs incurred as a direct result of the outage.
While Kaiārahi was out of service, Interislander was prioritising urgent freight that could not travel across the Cook Strait any other way.
“We have offered passengers booked on Kaitaki an incentive to rebook at a later date, to create more space for that freight. Some passengers have taken this offer up.
“We are actively monitoring capacity and working with all of our customers to move as many passengers and as much freight as we can as quickly as possible.
“Once again, we assure everyone we are doing all we can to minimise the disruption as much as possible and thank all our customers and passengers for their patience.”