Islanders are facing further disruption after a CalMac ferry developed a technical fault.
Its biggest ferry, the MV Loch Seaforth, developed problems with its engine control system.
Several sailings between Stornoway on Lewis and Ullapool on the mainland have been cancelled, as well as overnight freight services.
A number of CalMac’s vessels are currently out of action, with most of its ferries more than 30 years old and about half of its largest ships operating beyond their expected service life.
The latest disruption comes as sailings between Lochboisdale in South Uist and the mainland are set to be cancelled for several weeks from 16 April due to dry dock delays and technical issues.
CalMac said engineers are investigating the fault on Loch Seaforth and hope to resolve the issue “as soon as they possibly can”.
It said additional sailings for essential traffic would run between Uig on Skye and Tarbert on Harris on Tuesday night.
A CalMac spokeswoman said on Tuesday: “On arrival into Ullapool last night, MV Loch Seaforth reported an issue with its engine control and monitoring system - engineers are currently investigating the defect and are in contact with specialist contract support and will resolve the issue as soon as they possibly can.
“At the moment, traffic is being redirected on to alternative routes and additional sailings for essential traffic will operate between Uig-Tarbert-Uig tonight.
“Port staff will contact customers directly regarding these sailings, which will give priority to services such as food, medical supplies and time-sensitive loads. Remaining space will then be offered to general traffic.
“We are very sorry for the disruption and inconvenience that this technical fault is causing to our customers, and we are grateful for their patience.”
Four ferries to bolster the CalMac fleet are being built in Turkey, along with the Glen Sannox and the as-yet-unnamed hull 802, which have faced major delays and cost overruns during construction at the Ferguson Marine shipyard in Port Glasgow.
Scottish Liberal Democrat communities spokesman Willie Rennie said: “The ferry catastrophe is just like the crisis within the SNP, it’s all falling apart.
“But the political crisis is nothing compared to the chaos this is inflicting in the lives of islanders, even their typical resilience and patience seems broken in the face of yet another break down.
“No-one would blame them for taking action to get the SNP leadership to wake up.”
Scottish Labour leader Anas Sarwar said the cancellation of the service is “unacceptable”, adding: “The SNP’s neglect of the islands and their vital ferry services are coming home to roost with a broken down timetable that leaves islanders with only a once in a week lifeline to the mainland.
“If there had been effective political representation from the islands day after day on this issue in Westminster and Holyrood, the situation would not have come to this.”
Scottish Conservative transport spokesman Graham Simpson said the “neglect” of the services had now become a “full-blown crisis”.
Transport Scotland has been contacted for comment.
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