Engineers are investigating a 'technical issue' on board the Manxman, the Steam Packet has confirmed.
The vessel is making today's (Sunday's) outbound journey from the Isle of Man to Heysham at a reduced speed as a result of the problem.
It is understood the ship is due to arrive in England at around 12.50pm this afternoon.
The Manxman's return journey back to the island is now scheduled to set-off over an hour later than planned according to the Steam Packet.
It will set off at 3.30pm compared the original departure time of 2.15pm.
Passengers have been asked to check in for the sailing no later than 2.30pm.
In a statement released to Manx Radio during the outbound journey, the Isle of Man Steam Packet company said: 'The Manxman is currently travelling at reduced speed whilst the crew investigate a technical issue with the propulsion system'.