The Steam Packet Company says the Ben my Chree has been chartered to help a fellow Irish Sea ferry company over Christmas.
The vessel will operate a freight-only service between Heysham and Dublin for Stena Line.
The Steam Packet says the ship will be with Stena Line for at least a fortnight, although she can be recalled at any time if needed.
The charter started on Monday.
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Manx Grand Prix and Classic TT racing starts today
Racing to finish Tuesday in new MGP and Classic TT schedule