The problems affecting the Sound of Harris ferry service are now expected to last until Monday 24 August.
The service's regular vessel MV Loch Portain has been removed from service and is now berthed at James Watt Dock, in Greenock, where further investigations into the vibration levels on all four main engines and associated gearboxes will take place.
MV Loch Portain only returned from a very protracted service and engine upgrade in the middle of May.
Now CalMac say: "We have the full support of the OEM for the main engines and gearbox to aid these investigations and provide proposed engineered solutions to the vibration level experienced.
"We are expecting a full report with recommendations the week commencing Monday 10 August and a further update can be provided once more information is available."
MV Loch Bhrusda has been redeployed and will operate an amended timetable on Berneray – Leverburgh until Monday 24 August.
Until Monday (17 August) MV Glen Sannox will operate additional sailings on the Little Minch service. This provides support for interisland services.
But on Monday, to allow essential works to be carried out to MV Glen Sannox, the vessel will relocate to Stornoway and will operate the following additional sailing:
Depart Lochmaddy – 16:20. Arrive Stornoway – 19:20
View the amended timetable operating until Monday 24 August.
