THE supply of a faulty part has 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 one of the west coast of Scotland's busiest routes, to and from Brodick on Arran and 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The vessel was originally withdrawn in early January and was in dry dock for nearly a month with more than £1m of scheduled work being done to the vessel, including engine servicing.

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

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.

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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.

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

But it means that CalMac will have to cancel bookings this weekend as MV Isle of Arran, which can only carry 48 passengers and 76 cars will operate a one-vessel service for longer than expected.

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 user group official said: "It might be seen as churlish not to recognise there is light at the end of this very long tunnel, although we have been here before only to find something else has gone wrong.

"But to wait all these months for this ferry to return is clearly unacceptable and just adds more farce to an already farcical scenario with our ferries.   The new transport minister must be tearing his hair out over these continual issues."

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CalMac told a user group: "As a result of an equipment manufacturer supplying a faulty part (Highly elastic shaft coupling) for the repair to MV Caledonian Isles, the completion of repair work will be delayed and the vessel will now not be able to return to service on April 15, as previously announced. We held this part in stock to avoid potential months long delays caused by the lengthy lead times to receive a new one from order. This part connects the engine output shaft to the gearbox input shaft and ensures there is no torsional vibrations transferred between the engine and gearbox and manages any small misalignment, preventing damage to either.

"Following completion of engine trials, and as the vessel has been off service since early January, there is a need for additional operational testing of ancillary systems including ramps, mezzanine decks, mooring equipment and other services, to ensure the vessel is fully ready for service.

"Although all such systems have been maintained during the off-service period, including testing as applicable, only live use at an operational intensity can provide the necessary assurance that such systems have not suffered during the inactive period and are fully ready for use. This additional measure is intended to reduce the risk of in-service failure of operationally critical equipment which would have a negative effect on service.

"A phased return to service on Monday April 17 may allow MV Caledonian Isles to provide some unscheduled additional services to assist MV Isle of Arran on the Ardrossan - Brodick route, while these necessary checks are undertaken."