Maritime NZ has lifted the detention notice on the Interislander ferry Aratere.
The ferry has been in Picton, under the notice, since it ran aground shortly after leaving the port, bound for Wellington on 21 June.
Maritime NZ director Kirstie Hewlett said conditions have been imposed on the operation of the Aratere for safety reasons.
It will initially be allowed to return to service for crew and rail freight only, followed by trucks and their drivers, then a limited passenger service, before full capacity sailings are permitted.
The Wellington and Marlborough harbourmasters have also placed conditions around pilotage for the Aratere's exit and entry into Wellington and Picton.
Wellington Harbourmaster Grant Nalder said the restrictions meant no other large ships could be in the channel when Aratere was there, and a tug boat would have to meet the ferry upon arrival.
The ferry would also have a tug escort when it departed from Picton, he said.
Investigations into what caused the ship to run aground are continuing, and Hewlett said Maritime NZ's preliminary enquiries had found that the incident was not due to a crew member leaving the bridge to make a coffee, as alleged by NZ First.
She said in the coming weeks, Maritime NZ Inspectors would also undertake a focused audit on the Interislander fleet, looking at its processes, procedures, training, risk management as well as looking at how it brought on new equipment and familiarised its personnel.
"Maritime NZ's inspections and audits are a reflection of a point in time, and the operator, KiwiRail has the primary responsibility for day to day safe operation of the vessel, and its wider fleet."
Hewlett said Maritime NZ's investigation would explore the broad range of factors that caused the vessel to ground and would take several months.
KiwiRail told RNZ it did not yet know the timings around the first sailings because tugs still needed to be arranged.
"Once Aratere is back in Wellington we will be working through our internal processes and Maritime NZ's conditions. We will provide you an update on Aratere's return to service when we can."
In a statement, Interislander executive general manager Duncan Roy said the aim was to sail the vessel from Picton to Wellington on Thursday.
"We will then go through a graduated process as it returns to service."