The Steam Packet Company says its flagship ferry the Manxman won't be back in service until the end of November.
The company says specialist repairs were needed on two propulsion shafts, with problems found in July when the vessel was in drydock.
It had hoped the work would be finished this month, but now says the shafts have been sent to Denmark for up to eight weeks of work.
Managing Director Brian Thomson has apologised for any inconvenience and says affected passengers will be contacted directly.
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