The cost to build two CalMac ferries at the Ferguson Marine shipyard has increased by more than £70m.
However, if potential problems arise, this could increase to £84.1m.
In a breakdown of costs provided to STV News, the total budget in March was £125.5m.
But in a letter to the Scottish Parliament’s Transport Committee on Wednesday, the company confirmed that projected costs had soared to £209.6m.
If the nationalised shipyard meets its target and contingencies are not needed the difference would be £70.9m.
Initially, both ferries were due to cost just £97m.
In March, finance secretary Kate Forbes confirmed the project’s overrun had risen by £8.7m to between £122.5m and £126.5m.
Deputy first minister and acting finance secretary John Swinney said there would be a “rigorous approach” taken to scrutinising “this request for additional funding”.
The ferry known as hull 802 was due to enter service between October and December 2023 but is now not expected to be in service until summer 2024.
The target for completion for the other, the Glen Sannox, remains May 2023. However, this could yet be delayed by a further two months.
Swinney said: “Our priority is to undertake our own due diligence and this will be supported by external, independent financial advisors to ensure a rigorous approach is taken to scrutinising this request for additional funding.
“Let me be clear that no decision on any potential further investment has yet been made, and will not be made until this work has been completed. We are fully committed to financial transparency and I will update the Scottish Parliament in due course.
“The Scottish Government remains committed to a sustainable future for the shipyard and supporting the island communities which rely on this type of vessel, while safeguarding the hundreds of jobs for workers on the Clyde and the apprentices that are now beginning a career in shipbuilding at Ferguson Marine.”
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