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.