KiwiRail says it is ensuring customers using the Interislander ferry service will not be affected by the latest trouble with the newly-returned Aratere.
A return sailing by the ferry was cancelled on Wednesday - just one day after went back into full service - because it is too slow.
The ferry had been in a dry-dock in Singapore for repairs after losing a propellor in November last year.
The Aratere did three return trips between Wellington and Picton before it was withdrawn.
A KiwiRail spokesperson said it isn't clear why it is taking 15 minutes longer per sailing across Cook Strait. Timetables will be changed but all customers will be accommodated, he said.