CALMAC say one of its oldest ferries that has been filling in on on of its busiest routes is to come back into service this morning (Friday) after a successful repair.

The main Arran service  to Brodick was plunged into chaos with cars sent on 125 mile detours after 40-year-old MV Isle of Arran was sidelined after a leak found in the exhaust system into the engine room.

But now the Scottish Government-owned ferry operator says repairs have been successful.

Services were due to resume with the 7am sailing from Ardrossan today (Friday).

One of CalMac's busiest lifeline services lost its only boat on Thursday - at a time when they would expect to have two - after a breakdown.

CalMac told users that a repair was required for safety reasons.

The ferry operator said on Thursday that the crew were attempting a repair and external contractors were being mobilised to support.

Users were asked to detour onto the route to Lochranza on Arran to Claonaig, a hamlet on the east coast of the Kintyre peninsula in western Scotland, as an alternative.

By road, that would mean those travelling from Ardrossan going on a 125 mile detour to get to and from Claonaig - a journey that would take around three hours. The Ardrossan to Brodick ferry crossing usually takes just 35 minutes.

Buses were laid on from 3.30pm to take people from Ardrossan to Claonaig to provide a connection to Arran for foot passengers.  Buses are also to leave Brodick at 6pm for Lochranza to provide a connection to the mainland for foot passengers. There is  be a connecting bus from Claonaig to Ardrossan.

MV Isle of Arran had been taken off its normal Ardrossan to Campbeltown service to stand in on Arran for other ferries that have been sidelined for weeks due to problems found during an annual overhaul.

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It came after CalMac's biggest vessel MV Loch Seaforth which operates to and from Stornoway on the Isle of Lewis returned to action on Wednesday evening after being sidelined for three days, suffering engine issues on Monday evening.

The Herald:

The 31-year-old MV Loch Tarbert, 32-year-old MV Loch Fyne were added to the roster of vessels needing repairs over Easter Sunday and Monday causing further headaches for the Scottish Government-owned ferry operator. They have returned to service.

Three more of CalMac's fleet MV Caledonian Isles, MV Hebridean Isles and MV Clansman have remained out of action since the summer timetable began on April 1 having spent weeks on the sidelines for repairs after problems discovered after overhauls.

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MV Isle of Arran had been serving Arran for weeks on its own because of the issues with Caledonian Isles and MV Hebridean Isles, cutting the number of available vehicle spaces to about half.

It comes as a faulty part put back the return of one of CalMac's major ferries - MV Caledonian Isles after four months on the sidelines.

It had been hoped that the 30-year-old vessel would be back in full service in February to serve Arran but a series of setbacks has delayed a return.

User groups have been told by CalMac that as a result of an equipment manufacturer supplying a faulty elastic shaft coupling, the completion of repair works has been delayed yet again.

The vessel was originally withdrawn in early January and was in dry dock for nearly a month with more than £1m of scheduled work being done to the vessel, including engine servicing.

The Herald: Passengers wait to board the CalMac ferry, Caledonian Isles at  Ardrossan bound for Brodick on Arran. Photograph by Colin Mearns.

But inspections uncovered further issues including damage to both engines with the estimate for a return at three to five weeks.

In February, CalMac said Caledonian Isles would remain sidelined till at least March 1 following continuing concerns with its main engines.

By the end of February, it was confirmed it would be out till March 31, at least.

More recently it was said the vessel, which carries 1000 passengers and 110 cars would return on Thursday. That was then amended to Saturday.

CalMac have told local ferry users that repairs and sea trials are now due to be completed by Sunday and a one-day phased return is planned for Monday before returning to full service next Tuesday.

It meant that CalMac had to cancel bookings this weekend as MV Isle of Arran, which can only carry 48 passengers and 76 cars was to operate a one-vessel service for longer than expected.

READ MORE: Faulty part delays return of CalMac ferry sidelined for four months

The stricken MV Isle of Arran is due to operate services to and from Islay as a second vessel from next Wednesday. But it means the second vessel services will be cancelled on Sunday, Monday and Tuesday.

One ferry group official said: "We can only hope that MV Isle of Arran can remain in good order as CalMac try to get other affected vessels back on the water. But at its age it really should not be relied upon."

Last month ministers sanctioned a spend of £9m to charter an 'emergency' vessel for nine months in the wake of continuing disruption to lifeline ferry services.

MV Alfred is due to join the fleet on Tuesday when she will undertake berthing trials before being made available for service.

The vessel which is at the centre of a crash investigation dating back to the summer of last year, will be chartered from Pentland Ferries who will operate services on behalf of CalMac.

Critics have called it a "panicked decision".

All crew will be provided by Pentland Ferries who will be responsible for delivery of service and the operational, technical and safety management of the vessel, including maintenance, repair, overhaul and provision of crew throughout the charter period. It comes amidst widespread disruption to services because of issues with vessels discovered during the annual overhaul process.