The Transport Accident Investigation Commission has opened an inquiry into last night's incident where interisland ferry the Aratere lost a propeller during a Cook Strait crossing.
Two investigators boarded the vessel this morning, the commission said.
"Their initial focus will be on gathering information about the incident voyage and interviewing the relevant crew members.
"The commission's inquiry will aim to identify what factors may have led to the incident, and make any recommendations that might prevent a recurrence.''
The Aratere has been taken out of service while the fault with a propeller shaft is assessed, Interislander General Manager Thomas Davis said this morning.
The ferry suffered a mechanical issue with one of its two shafts yesterday, he said.
"Divers were put down to examine the shafts to ascertain the damage upon her arrival in Wellington last night and we can confirm that one of the shafts and the propeller needs to be replaced,'' Mr Davis said.
All Aratere sailings for the rest of the week have been cancelled while surveyors assess the damage.
The Arahura will take over the ferry's timetable from this afternoon. Contingency plans are being worked on should the Aratere be out of service for more than a week.