Answering questions from MSPs in Holyrood, the finance secretary emphatically rejected accusations from the tycoon the deal for hulls 801 and 802 were rushed for political purposes.
Mr McColl told the BBC on Tuesday morning that there had been a “fabulous propaganda exercise" by the SNP to shift blame on to Ferguson’s for the five year delay to the vessels which were supposed to go into service in 2018.
Ms Forbes said it was “entirely wrong” the contract award was “rushed”, stating that the timetable did not “support that notion” and that all procurement processes were followed.
Attacking Mr McColl, she added: “Contrary to what Jim McColl said this morning on the BBC, it was the chief executive of CMAL and Jim McColl himself who signed the contract.
"This is a man with a clear interest in shifting the blame on others when the route course ultimately to the delays of these important vessels was the construction under FMEL.”
In 2019, the shipyard was nationalised by the Scottish Government in a bid to save jobs, but the construction of the two lifeline ferries have been beset by delays.
Central to the issues with the contract was the lack of a full builders refund guarantee which would have allowed the Scottish Government to claw back money spent on the vessels in the event of a delay.
However, FMEL said they were not able to offer a full refund guarantee, which raised concerns amongst CMAL.
These concerns were ignored by the government, but no documentary evidence exists to state why, a scathing Audit Scotland report on the fiasco states.
Ms Forbes told MSPs: “There were no concerns raised at the point of announcing the preferred bidder in August 2015, and that is why the preferred bidder was announced based on the advice of CMAL, FMEL clearly scoring the highest score overall.
"When concerns were raised, mitigations were put in place, that is all very well documented in the Audit Scotland report.”
Ms Forbes also contradicted Mr McColl’s claim that he did not know of CMAL’s concerns around the contract, claiming that FMEL were “crystal clear” about the concerns raised at the time.
She said: “On the contrary to public statements made this morning, FMEL were crystal clear about the concerns that were raised about their inability to provide the full refund guarantee.
"The Audit Scotland report refers to the fact that when the announcement was made about the preferred bidder in the August, no concerns were raised.
"A number of weeks later, concerns were flagged about the required refund guarantee.
"At that point, FMEL would have been fully involved in the discussions around the mitigations that were required because there was not a full refund guarantee in place.
However, despite being asked by Scottish Labour’s transport spokesperson Neil Bibby whether cabinet discussed this issue, the finance secretary failed to answer whether the cabinet had been aware of the concerns.
Mr Bibby added: “Only the First Minister can clear up the questions about what has went wrong here and who was involved when.
"We need honesty and openness about this. We cannot afford secrecy and cover-up because taxpayers, in the midst of a cost-of-living crisis are paying for the cost of this government’s failure.
"Kate Forbes has said today there was no rush and no politics, I don’t think anyone thinks that is credible.”
Transport spokesperson for the Scottish Conservatives, Graham Simpson, accused the finance secretary of failing to answer “straightforward” questions on why the government ignored concerns raised by CMAL about the contract.
He said: ““We heard plenty of waffle and a clear attempt to pin the blame for this mess on Jim McColl – but still no clarity.
“The bottom line is the SNP Government played fast and loose with a huge amount of taxpayers’ cash by agreeing to a contract without basic financial safeguards. Until they have an explanation for that, the questions will keep coming.
“It’s clearer by the day that we need a full, independent inquiry to get to the bottom of this murky saga.”
Willie Rennie, economy spokesperson for the Scottish Liberal Democrats, called on the First Minister to make a statement to Holyrood on the issue and accused both Ms Sturgeon and Ms Forbes of misrepresenting the Audit Scotland report.
He said: “It is shoddy behaviour from the First Minister and the Finance Secretary to claim support from Audit Scotland when the words describe the Scottish Government’s own assessment of the procurement process.
“It’s a blatant attempt to pass off the government’s own judgement as an independent assessment.
“It is increasingly difficult to believe what comes out of ministers' mouths on this topic.”