CalMac's largest ferry out of Ullapool-Stornoway service for engine repairs
CalMac has said its largest ferry has broken down and will need to be taken to dry dock for "major" engine repairs.
The MV Loch Seaforth has been taken off the Ullapool-Stornoway route and is likely to be out of service until at least the end of April.
CalMac apologised to customers for the inconvenience that will be caused.
The MV Isle of Lewis will pick up the day service for passengers and freight from Thursday.
The overnight freight service has been suspended until further notice.
The Isle of Lewis has been taken off its usual route between Castlebay on the Isle of Barra and Oban in Argyll.
Another ferry, the MV Lord of the Isles, will combine the Lochboisdale, South Uist, and Castlebay services.
Leaders at Western Isles Council - Comhairle nan Eilean Siar - have been critical of CalMac's local ferry services, which they have described as "unacceptably poor".
The comhairle said islanders had "unfortunately become rather used" to disruption, especially over the past two winters due to issues with what it called CalMac's "ageing fleet".
The local authority said it had concerns about the smaller Isle of Lewis being able to cope with demand when Scotland's Covid restrictions are further relaxed on 26 April.
It has also warned of a potential impact on island firms getting their products to the mainland.
Largest and fastest
CalMac said the Loch Seaforth had suffered a major failure of the port engine.
The ferry operator said: "It is expected that the vessel will be out of service until at least the end of April to allow the engine issue to be thoroughly investigated and repaired.
"We appreciate the importance of the passenger and freight service on this route and apologise for the inconvenience this amended timetable may cause."
Amended ferry timetables for the affected routes are available on CalMac's website.
The 116m-long (380ft) Loch Seaforth can carry up to 143 cars and 700 passengers.
Built in Germany at a cost of £42m, the ferry has been in service since 2015 and is the largest and fastest in CalMac's fleet.
The ferry carried its first passengers in February 2015 but just weeks later was withdrawn from service twice, first for repairs to a faulty ventilation fan and then again after a pipe carrying lubricants to the gearbox split.