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.
Fuel firm says "fingers crossed" for calmer energy costs
Ring doorbells will need data protection registration - but shouldn't cost you money
Hospice UK head calls Island cuts "cack-handed" ministerial muddle
Bus drivers voting on "final offer" from government
Vampire show featuring Manx ferry cancelled
Did chief minister's message spark fuel panic-buying?
Joe Locke lands purr-fect new role!
Steam Packet fuel surcharge isn't about profit, says chief minister