Two new Spirit of Tasmania ferries, yet to start sailings because of a failure to build a berth, require further hull upgrades to prepare for extreme weather.
One of the replacement vessels has been in Hobart since August 23 for its final fit out, while the other is in Finland, where it was constructed.
They are expected to be in service in late 2026, years behind schedule, when a delayed berth in the northern Tasmanian city of Devonport is completed.
Failure to build the berth in time for the ships' completion has made international news and resulted in one being kept in Scotland during an unsuccessful lease attempt.
A "recovery team" tasked with getting the ships' delivery back on track recently said it was upgrading hull specifications to further prepare for rare or extreme weather or power failure.
Infrastructure Minister Kerry Vincent said state-owned ferry operator TT-Line hadn't yet determined the extent and cost of the upgrades.
TT-Line was double checking all calculations made in the design of the ships as part of the process, Mr Vincent told reporters on Tuesday.
A TT-Line spokesman said the "recovery team" had identified the need for minor hull upgrades to further prepare for rare or extreme weather events or power failure.
"There is an extremely low risk of a rare event occurring," he said.
"Any modifications required will be completed within the current budget and will have no impact on the commencement of service date."
Labor opposition MP Anita Dow said it was concerning the need for a hull upgrades on the ships, which have cost $930 million combined, had only been detected at this point.
Taxpayers deserved more information about why the hulls were being upgraded and how much it would cost, she said.
Spirit of Tasmania IV is expected to relocate from Hobart to Geelong in October. It cost the state $6.4 million to berth it in Scotland.
Costs for the berth at Devonport have blown out from $90 million to $493 million.
The saga around the berth delay resulted in Michael Ferguson resigning as deputy premier and infrastructure minister and moving to the back bench in October 2024.
