It has also been revealed human error is to blame for $9 million worth of upgrades needed for the vessels and their yet-to-be-completed berth in Tasmania.
The two replacement vessels aren't expected to be in service until late 2026, years behind schedule, because a berth in Devonport wasn't built in time for their arrival.
The saga, which caused one of the new ships to be kept in Scotland for months, has been dubbed one of the biggest infrastructure stuff-ups in Australia's history.
Tasmania's government on Monday announced it would give the ship's state-owned operator TT-Line an injection of $75 million in the November 2025/26 budget.
The funds would deal with "medium-term" financial issues, TT-Line chair Ken Kanofski told reporters.
"What we said is 'we need a buffer', we don't want to run too close to the wind," he said, adding the company had asked the government for $100 million.
"We're now turning attention to the long-term future of the business (and) operating in a financially sustainable way."
TT-Line has been dealing with cost blowouts, including to the $493 million berth in Devonport that was originally priced at $90 million.
In July, it increased its borrowing limit from $1.035 billion to $1.445 billion.
Mr Kanofski said $9 million would need to be spent on strengthening the hulls of both ships and altering shock-absorbing wharf fenders at the Devonport berth.
It was revealed three of the fenders were built stronger than required because TT-Line provided incorrect specifications.
"It was an error. It was clearly human error by TT-Line in 2023," Mr Kanofski said.
The $9 million wouldn't add any additional costs to the project and would come from a contingency buffer, he said.
Labor opposition MP Dean Winter said Tasmanians were being forced to pay the price for incompetence.
"The bill from the biggest infrastructure stuff up in Tasmanian history keeps growing," he said.
The state government hasn't ruled out giving TT-Line the remaining $25 million of the company's request if needed.
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