SCOTLAND'S lifeline ferry network faces even more disruption after plans to have its largest vessel back in service after repairs were put off for a fourth time.

MV Loch Seaforth was taken off the Ullapool-Stornoway route by CalMac, the publicly funded ferry operator, to be taken into dry dock for "major" engine repairs nearly a month ago.

State-owned CalMac had initially said the eight-year-old vessel would out of action until "at least the end of April", then later said that it would be back by May 4 after repairs took longer than expected.

A day later CalMac then said she was expected back in service by May 17 at the earliest.

READ MORE: CalMac ferry network crisis as breakdowns cause three day island freight shutdown

Now specialist engineers carrying out final testing on the Loch Seaforth have identified that further work is needed on one of her engine bearings.

So as the islands start to open up to visitors with the easing of Covid-19 restrictions, the return of the vessel has been shifted again to May 21 "at the earliest".

HeraldScotland:

It comes a matter of days after Scotland's crisis hit lifeline ferry network came under fresh fire after a new series of breakdowns and setbacks with five of its fleet leading to service cancellations and restrictions as new pressure is put on ministers to take urgent action.

The Herald revealed how the failure of Loch Seaforth resulted in cuts to other services across the ferry network as vessels relied on with other routes were shifted around to accommodate.

Campaigners had described the situation as a "national scandal" and that those responsible should already have lost their jobs for the state of Scotland's ferries.

CalMac has said Loch Seaforth repairs are "progressing" and that it is due to leave the James Watt Dock in Greenock for two days of sea trials on May 17 before returning to the Stornoway-Ullapool route on May 21.

The ferry operator said the dates "remain under review and are subject to change if required".

It means that the temporary shifting of ferries to cover for Loch Seaforth's loss will remain in place. That means MV Isle of Lewis, which was taken off its usual route between Castlebay on the Isle of Barra and Oban in Argyle to support the Loch Seaforth run will remain.

It means the one of Scotland's busiest ferry services, the Ardrossan to Arran route, will remain serviced by one vessel, rather than two.

According to the Arran Recovery Group, the shifting of the ferry for the start of the summer tourist season will cost the island more than £500,000 in lost business.

The 38-year-old MV Isle of Arran - which normally runs on the Ardrossan to Arran route - and was taken off freight service duties on the Ullapool-Stornoway crossing because of stabiliser problems, resulting in a shutdown on services for over three days last week, will remain operating on the "more sheltered" Islay run.

There was criticism when it emerged that as Isle of Arran only had space for four lorries.

The 36-year-old MV Hebridean Isles, ended up replacing the Isle of Arran on the Stornoway crossing on Saturday causing cancellations on its usual Kennacraig to Islay.

It means the Ardrossan to Campbeltown service which has been out of action since Loch Seaforth's major engine problems, will remain so.

Robbie Drummond, managing director of CalMac, said: “We will continue to keep all customers informed of updates and we are very grateful for their patience and understanding at this time.

“Any change to services can be challenging for our customers and the communities we serve, and we apologise for the disruption this will cause.”

It comes after CalMac's tickets and reservations phone lines which were out of action for the whole of Wednesday, were back in service yesterday (Thursday).

At the weekend, the 23-year-old car ferry MV Clansman which runs the Oban-Coll-Tiree route was due to be out of action because a shaft needed replaced and an amended timetable was in place.

That came two weeks after it returned to Oban with all services cancelled for the rest of the day after it developed a fault. CalMac said at the time that the issue was being investigated.

The issues come off the back of the country's ferry building fiasco with two lifeline vessels being built at nationalised Ferguson Marine, owner of the last civilian Clyde shipyard. They were due to be in service in early 2018, are now up to nearly five years behind schedule and their is now over double the original £97m contract.

The first of the ferries the MV Glen Sannox is now destined for the Arran to Ardrossan route - Scotland's busiest ferry crossing - between April 2022 and June, 2022.

Ferguson Marine, led by tycoon Jim McColl went into administration in August, 2019 following a dispute with Caledonian Maritime Assets Ltd (CMAL) - the taxpayer-funded company which buys and leases publicly owned CalMac's ships on behalf of the Scottish government - over the construction of the ferries under the fixed price contract.

The Scottish Government then pushed ahead to take full control of of the shipyard company as it went under with blame attached to soaring costs of the ferry contract.