One of the biggest and oldest vessels in Scotland's lifeline ferry network is set to be sidelined for nearly three months.

The 30-year-old MV Caledonian Isles which serves on the Arran route, one of the busiest on the Scottish coast, and is due to be replaced, has been out of action since going for an overhaul at the start of January.

It was sidelined for over three months with further steelwork and engine difficulties this time last year.  Further steelwork problems were attributed to a further period spent in the yard in early 2022.

The vessel has been found to have had major technical problems and is now not expected back till at least the end of next month.

Users have been told that the vessel needs "extensive steelwork" leading to concerns that it is suffering rust issues.

It comes ferry operator CalMac completed a temporary switch of its sole passenger ferry MV Isle of Arran to Troon for four days in the wake of safety issues at Ardrossan - amidst fears the shift could eventually become permanent.

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But the move has been hit with difficulty, with some complaining about not being able to get tickets for the crossing.

It later emerged early Thursday afternoon that all sailings including freight operated by MV Isle of Arran and MV Alfred to Brodick were cancelled and remain cancelled on Friday.  A limited time timeable was due to operate on Saturday and Sunday.

The Herald: MV Alfred is now on the Arran route

MV Caledonian Isles, which also serves Arran is to be moved to the Cammell Laird yard facility in Liverpool for repairs and there is a race against time to get it available in time for the summer timetable to kick in on March 29. CalMac has said it is expected to be sidelined for four to six weeks.

But user groups have been told that a true assessment and timeline will only be known in the coming weeks, once the vessel has been moved and a full assessment is made.

It is understood that underwater areas of the vessel need to be accessed.

"Our team is focused on doing all we can to support our services and minimising the effect of annual overhaul and such challenges as the weather and closure of the Irish berth on our customers," the ferry operator said.

Users were told that it was appreciated that the emergency timetable was "very limited but it is all that we are able to operate with current resource".

It is the second successive year that the vessel has had an extensive period on the sidelines for repairs.

When it went for an annual overhaul in early January 2023, it was due to return to service on February 2 but that was delayed for, again, additional steel work and engine repairs being required.

CalMac initially announced a provisional return date of February 28 but this was later pushed back to March 31 and then pushed back further to mid-April.

MV Hebridean Isles was scheduled to operate alongside Isle of Arran but significant technical faults saw her providing a freight-only service between Brodick and Troon, before being withdrawn from service altogether in late February after itself hitting issues from the previous Boxing Day.

The Scottish Government-owned ferry operator made moves to pull out of Ardrossan in the wake of safety issues and adverse weather.

They moved to begin trial berthing MV Isle of Arran, the only ferry carrying passengers to and from Arran at Troon.

It began operating on a "temporary" basis from Troon on Thursday in a move that is due to end on Sunday.

But there has been concern that it is the first step to a permanent move for the services from Ardrossan, with the £1m-a-month Scottish Government-chartered emergency vessel MV Alfred already operating from there.

The Irish Berth at Ardrossan, which had been used by an emergency CalMac ferry for the key lifeline route to Arran was put out of action on January 18 when the harbour authority ordered all users to cease operations. It has now been shut permanently.

Video: MV Caledonian Isles

MV Alfred, as it is unable to use the alternative Ardrossan berth, ended up sent to Ayr and has been providing a freight-only services from Troon.

It is now being redeployed from Monday to serve Uig on Isle Of Skye, Lochmaddy on North Uist and Tarbert in Harris between Monday 12 and Friday 16 February. This deployment is to allow MV Hebrides to travel to dry dock for planned annual overhaul.

One ferry user official said that there has been complaints about difficulties in getting tickets for Arran crossings this holiday weekend and was surprised that the extra capacity had been removed.

"Where we are with MV Caledonian Isles, quite frankly, is that she shouldn't be operating," he said. "One of the two ferries currently still being completed at Ferguson Marine would be operating here instead. At her age, she is well past retirement age and that is where we are with too much of CalMac's fleet."

Charles Currie, a retired former tourism manager for Isle of Arran then director of marketing for Ayrshire and Arran Tourist Board as well as former chairman of the Isle of Arran Ferry Committee said he had found difficulty accessing ferry tickets for the weekend and said  "This is a holiday weekend and businesses and families are expecting visitors and students to be on the island.   Does this have more to do with Ardrossan Harbour than the weather? "

Both ferries, Glen Sannox and Glen Rosa were due online in the first half of 2018, with one initially to serve Arran and the other to serve the Skye triangle routes to North Uist and Harris, but are at least six years late, with costs expected to be quadruple the original £97m contract. It has been confirmed that both are now to serve Arran.

Glen Rosa was meant to be delivered to CalMac in August 2018, but that is currently scheduled for May 2025. Glen Sannox, was launched by Nicola Sturgeon nearly seven years ago and is due for delivery in the spring.

But the dates of arrival have been constantly in a state of flux as their construction has been plagued by design challenges, cost overruns and delays.

The Herald revealed that Ardrossan may not ever by used to take much delayed and over-budget ferries despite the green light being given for upgrade works by the current First Minister six years ago.

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The Scottish Government confirmed that no decision had been made over whether Ardrossan would remain the mainland port for the Arran service – placing serious question marks over the upgrade project.

The full business case for a project to upgrade Ardrossan to allow the two ferries to berth there and take the 'green fuel' LNG remains incomplete and there is even uncertainty over the project costs. Consequently, the project has still to be put out to tender.

It is understood there have been issues over how the cost – which in 2022 was estimated at £40m – would be divided between the Scottish Government quango Transport Scotland, the harbour owner Peel Ports and North Ayrshire Council.

The Scottish Government-owned ferry operator CalMac has already been planning to use Troon rather than Ardrossan for the two ferries that will serve Arran. That was when it was hoped that the first of the vessels would be ready for passengers in the Spring of last year.

A CalMac spokesman said:" With regards to MV Caledonian Isles, based on the current assessment that has been possible, indications are that the repairs could take in the order of 4-6 weeks.

"This requires that the underwater areas of the vessel can be accessed, and the ballast tanks are emptied in the dry dock. The assessment will require intrusive works, which will need to be coordinated carefully and systematically as repairs are required in adjacent locations.

"We will work with the Classification Society [the non-governmental organisation that establishes and maintains technical standards for the construction and operation of ships and offshore structures] and the shipyard to clearly define and prioritise the work scope. Underwater repairs will be completed first, with 24-hour working being completed where possible."