The Port Glasgow shipyard said the latest delivery date for Glen Sannox, earmarked for the main Arran route, remained between July 25 and September 25 – four years late.
But its turnaround director Tim Hair said in a report published today that was “achievable, but remains challenging”, and a planned increase in production in January and February was “critical to the achievement of this delivery schedule”.
He warned cases of the Omicron variant were increasing among staff, leading to more self-isolation.
Mr Hair said: “It seems likely that we will experience significant disruption in January and that, in turn, might result in lost productivity.
"The progression of the Omicron variant has the potential to cause severe disruption at a critical time, but this cannot be quantified at this time.”
The further potential setback comes after completion dates for the ferries were put back by up to five months last year by a skills shortage and the pandemic.
Mr Hair said the rate of pipework installation on Glen Sannox, known as hull 801, had increased, but “has not achieved planned levels” and it was a “critical risk to the delivery of 801”.
Mr Hair said completion of the second ferry, known as hull 802 and destined for the Uig-Tarbert-Lochmaddy routes between Skye and the Western Isles, remained between April 3 and July 3 next year.
However, long-running discussions with the Scottish Government over the “ducktail” section of its hull, designed to increase speed and not fitted to Glen Sannox, “have the potential to impact the schedule for delivery of the vessel”.
Mr Hair’s latest quarterly update to the Scottish Parliament’s net zero, energy and transport committee also stated that “much of the equipment for the ferries has been installed since 2016 and may have deteriorated”.
"Although surveys, remediation and replacement have taken place under [Scottish] Government ownership, there is an unquantifiable risk that equipment problems may emerge during commissioning,” he said.
Mr Hair, drafted in after the Scottish Government took over the struggling yard in 2019, is to be replaced next month by new chief executive David Tydeman.
Scottish Conservatives transport spokesperson Graham Simpson said: “It is quite clear that both vessels may not be finished on their new extended timetables.
“Incredibly, there are still discussions about the design of 802, which could also impact on the delivery of that vessel.
"This should have been sorted out ages ago.
“Disruption due to Omicron could make matters even worse.
“This ongoing farce needs to be sorted out, and fast.”
Scottish Labour transport spokesperson Colin Smyth said: “The sorry saga of Scotland’s ferry fiasco rumbles on, but sadly not to a conclusion anytime soon.
“Despite the longest delivery schedule in shipbuilding history for two ferries, it will send alarm bells ringing that management at the yard are describing the delivery date of four years late as still challenging to meet.
"The failure to get a grip when problems were flagged up years ago has been an utter dereliction of duty by ministers.
"Unfortunately, it is the taxpayer and islanders who are paying the price for this Government’s incompetence.”