The two new Spirit of Tasmania ferries are no longer using autopilot in Port Phillip Bay near Geelong as a precaution, according to operator TT-Line. This decision follows separate steering faults on the vessels in recent weeks.

The Australian Transport Safety Bureau (ATSB) is investigating the steering incidents, with a report expected by the middle of next year.

Spirit IV experienced a primary steering system failure last Thursday during its fifth passenger voyage. The incident occurred as the vessel neared Port Phillip Bay en route to Geelong, when steering control was switched from autopilot to manual mode. A back-up steering system was used, and a tugboat escorted the ferry to Geelong, causing a delay of about four hours to its scheduled arrival. Track maps showed Spirit IV made several turns outside Point Lonsdale before entering the bay.

This incident followed a separate steering fault in October on its sister ship, Spirit V, which caused it to briefly move outside the bay’s charted shipping lane during a trial voyage.

TT-Line chairman Ken Kanofski stated on Monday that last week’s incident on Spirit IV involved a “frustratingly minor issue.” He told 936 ABC Hobart that an inspection in Geelong found a “frustratingly minor issue with mechanical electrical processes in the steering console itself,” which was rectified.

Mr Kanofski confirmed that autopilot is currently not being used when approaching and departing Geelong in Port Phillip Bay. However, he noted that autopilot would still be used once the ships reach the open waters of Bass Strait. He added that autopilot has never been used for arrivals and departures at Devonport due to the shorter distance and different entry to port, which is always a manual process.

TT-Line has “no plans to resume the use of autopilot for all channel and close quarter navigation” and will review the situation once the ATSB releases its report.

On Sunday, Spirit IV conducted a “planned, routine check of its equipment” off Devonport, described by TT-Line as part of ensuring the vessel’s safety. The new Spirit of Tasmania ferries began carrying passengers across Bass Strait in late October.