Probe widens after steering failure on Spirit of Tasmania ferry

The transport safety watchdog has expanded its probe into steering issues on the new Spirit of Tasmania ferries after the primary system "failed" on one of the ships on Thursday.

The Australian Transport Safety Bureau (ATSB) was already investigating an incident involving Spirit V during a trial voyage on October 24.

During that incident, steering problems involving the autopilot briefly caused the ship to move outside the charted shipping channel limits off Geelong.

Yesterday, Spirit IV suffered its own steering issue that resulted in a tugboat escorting the vessel to Geelong as a precaution.

At a Public Accounts Committee hearing today, TT-Line's chief executive Chris Carbone said the new ships had two separate steering systems as a redundancy.

"Those systems are independent of each other and, in fact, they're made by different manufacturers and that's part of the whole safety systems on board the ship," Mr Carbone said.

"So [in] yesterday's incident, the primary system failed.

TT-Line chairman Ken Kanofski apologised to passengers for the four-hour delay caused by the issue, but said safety took precedence over scheduling.

"Yesterday we had an operational issue," Mr Kanofski told the committee.

"All of the backup systems and procedures kicked into place.

"All of the protocols were followed.

Mr Carbone said it was not yet known if the steering issues on both vessels involved the same root cause.

He said TT-Line had appointed an independent investigator to assess both incidents.

"I want to assure everyone that these new ships are safe and they also have full redundancy across all the operating systems on the ship," he said.

Spirit IV resumed service overnight.

'Highest investigation priority': ATSB

The ATSB said yesterday's incident would now be included in a wider probe of the October 24 incident.

"The expanded investigation will involve the download of both ships' vessel data recorders for the relevant voyages, examining the ships' equipment, interviewing involved crew and other relevant personnel, and analysing records and documentation," the ATSB said.

The ATSB is also investigating a third incident in which the master of Spirit I was forced to abort entry into Port Phillip Bay due to a position error on the ship's electronic chart display on October 15.

Spirit i and Spirit ii have since been retired from service as part of TT-Line's delayed and over-budget ferry replacement program.

The two older ships are berthed in Victoria while TT-Line tries to secure buyers for each vessel.

"We are in very advanced discussions," Mr Kanofski told the committee.

"Further advanced on one than the other.

The committee was told it was hoped one of the ships would be sold by the end of December and the other by mid next year.