P&O Ferries has said a full investigation will be carried out after a vessel travelling between Cairnryan and Larne lost power off the Co Antrim coast.
The European Causeway, which can carry 410 passengers, was adrift five miles off the coast of Larne in the Irish Sea for more than an hour on Tuesday afternoon.
It left Cairnryan at about noon and was due to arrive at Larne Harbour at 2pm but got into trouble at around 1.30pm.
It has since docked at Larne harbour after regaining power. No injuries were reported.
P&O has cancelled its later sailing from Larne to Cairnryan.
Earlier, the Marine Traffic website stated the vessel’s automatic identification system status had been set to “not under command” which is reserved for use when a vessel is “unable to manoeuvre as required by these rules and is therefore unable to keep out of the way of another vessel”.
A spokesperson for P&O Ferries said it had been a temporary issue and the European Causeway had travelled to Larne “under its own propulsion”.
The spokesperson said: “Following a temporary mechanical issue, the European Causeway is now continuing on its scheduled journey to the Port of Larne under its own propulsion, with local tugs on standby, where it will discharge its passengers and cargo as planned.
“There are no reported injuries on board and all the relevant authorities have been informed.
“Once in dock a full independent investigation will be undertaken.”
A RNLI spokesperson said that three lifeboats had been sent to the scene.
The spokesperson said: “Three RNLI lifeboats were requested to launch this afternoon to assist a passenger ferry in difficulty one mile south east of The Maidens. Larne RNLI’s all-weather lifeboat launched at 2.17pm while Red Bay RNLI’s all-weather lifeboat launched at 2.35pm followed by the inshore lifeboat at 3pm.
“The ferry gained power again and was escorted back into the Port of Larne by all three lifeboats which were then stood down.”
A coastguard helicopter was also tasked from Scotland and a cruise ship in the area was on standby in case assistance was needed.
The Rail, Maritime and Transport workers’ Union (RMT) said the incident was “deeply concerning, not least for the agency crew and passengers on board”.
This is the latest in a series of difficulties for P&O which was widely criticised when it sacked 800 workers in March without notice.
The European Causeway was then detained at Larne after an initial inspection by the Maritime and Coasguard Agency (MCA) on March 25 uncovered 31 safety failings.
This was due to safety concerns after the sacked seafarers were replaced with cheaper agency workers.
The ship was cleared to resume serving the Larne-Cairnryan route a fortnight later following another examination.
Passenger Jonny Wilson was with his family on the ferry when the power went off.
He told the BBC: “The emergency lights go on. Different bits of the ship were dark.
“Slowly we came to a stop. They put the anchors down and we just sat there.”