The two Calmac ferries being built at Ferguson shipyard face further delays after safety regulators demanded design changes.
Extra staircases will have to be installed on Glen Sannox and Hull 802 in order to satisfy the Maritime and Coastguard Agency (MCA).
The work means planned sea trials of the Glen Sannox have been delayed until the first quarter of next year.
More details of the impact of the changes will be given next month.
But the announcement, which has also seen delays to the commissioning of the Glen Sannox’s fuel system, will raise concerns that the ship will not be in service with Calmac in time for the start of the summer season.
Once the Glen Sannox is handed over to CalMac, the ferry operator will need to conduct its own trials and on-board training, a process which could take up to eight weeks.
Ferguson Marine previously said the Glen Sannox, which will operate on the on the busy Arran route, should be operational in the spring of 2024.
In a letter to Holyrood’s transport committee, Ferguson Marine boss David Tydeman said he hoped to reach final agreement with the MCA in the next two weeks over a plan to make the modifications, which also includes widening some doors on the vessels.
He added: “This means the sea trials will move into the first quarter of the new year and the commissioning of the Liquefied natural gas system at Troon (which must be done after dry docking) will also be moved to after Christmas”.
Both ships were originally meant to be completed in 2018 at the Port Glasgow shipyard for £97m, but the build has been plagued by repeated cost overruns, delays, mistakes and design issues.
A bitter dispute between the yard’s former owner Jim McColl and government owned ferries agency CMAL saw the yard nationalised in 2019, with both sides blaming each other for what had gone wrong.
The final cost of building Glen Sannox and Hull 802 will now be more than £300m.
