The Loch Seaforth will operate 24 hours a day on the Stornoway to Ullapool route carrying passengers and vehicles during the day, and commercial heavy lorries overnight. It will thereby replace both CalMac's car ferry and its freight vessel on the route.
It had been due to undergo sea trials next month and be fully operational from September 8. But it now looks as though the ferry will not be handed over to CalMac until the end of September and not be sailing on the route until October.
A spokesman for CalMac said: "We are revising our plans in light of this delay and cannot give a date for her introduction into service at this stage."
The ferry is the property of the publicly owned Caledonian Maritime Assets Ltd (CMAL) fleet, who said the Loch Seaforth was in the final stages of construction in the shipyard at Flensberg.
CMAL said the handover was later than anticipated due to an unavoidable delay in the installation of electrical services throughout the vessel. This has had a knock-on effect to other trades and services.
Tom Docherty, chief executive officer of CMAL, said: "A team from CMAL is on site in Germany working closely with the shipyard to assist and ensure the revised delivery plan is achieved and, more importantly, that the vessel is completed to a high standard. I look forward to welcoming her to Scotland later in the autumn."