CalMac has said the return to service of one of Arran’s main ferries could be delayed by up to five weeks.
The MV Caledonian Isles was withdrawn from the Ardrossan-Brodick route for annual maintenance.
It had been due to leave a yard in Greenock on 3 February, but CalMac said the boat required additional work including replacing some steelwork.
More than £1m-worth of scheduled work was being done to the vessel, including a service of its engines.
It has been in dry dock since 9 January.
Engineers carrying out the overhaul have uncovered damage to both engines, including a turbocharger rotor and bearings.
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CalMac, which has previously spoken of the challenges of maintaining its ageing fleet of ferries, has apologised for the delay affecting the Caledonian Isles.
It said its initial plans to cover the ferry’s absence would be in operation until 16 February, and kept under review.
The main Arran service is currently being covered by MV Isle of Arran, supported by MV Hebridean Isles operating a freight service between Troon and Brodick.
CalMac said there were also sailings between Lochranza and Claonaig.
Chief executive Robbie Drummond said: “We apologise for the impact this will have on the Arran community, we know how disappointing it will be for customers who were expecting normal service to resume next week.”
He added: “I visited MV Caledonian Isles in dock this week and can assure customers that extensive work is being carried out to ensure her safe return to service.
“I would like to thank our teams who are working hard to find solutions and provide the best service possible during this period.”
This month had already seen delays to one of Mull’s ferries returning to service.
The MV Isle of Mull broke down when it was heading back to the west coast following a routine refit in Aberdeen – it had to be towed to Orkney.
Sailings on CalMac’s Skye triangle are currently disrupted due to essential repairs to the pier at Skye’s Uig harbour.
The service, which provides a connection between Harris and North Uist to the mainland, is to resume on 13 March before being shut again for six weeks from 30 October.
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