French maritime authorities are investigating Brittany Ferries' flagship which was hit by a 40ft (9m) freak wave in gale-force winds.
The Pont-Aven is at Roscoff
The Pont-Aven was struck in the Bay of Biscay as it travelled from Plymouth to Santander at 2232 BST on Sunday.
Five passengers and one crewmember were slightly injured as a window smashed and the ferry was diverted to Roscoff.
Brittany Ferries said it was a random incident that could not have been predicted, despite recent high winds.
Spokesman Steven Tuckwell said: "The Pont-Aven has been ploughing back and forth between Plymouth and Santander for the past week during high winds and bad weather, but in the last two years of operating it has never encountered this kind of freak activity before."
Passenger Carol Newstead, from Newton Abbot, Devon, said: "There were people near us that had children who had never been on a ferry before.
"They were very scared and very worried.
"No-one knew what to do. It took quite a long time for any information to come through."
Coastguards said they took about a dozen calls from passengers and their relatives who were worried about the £100m vessel.
But Mr Tuckwell said there was no panic on the vessel.
He said: "The captain sounded the alarm.
"Most of the passengers were in restaurant or bar at the time the waves hit, so there were only about 10 or 20 people directly affected."
After the extent of the damage to the ship is assessed, the ship will be moved to Brest for repairs.
The ferry company has said it hopes the Pont-Aven will be ready to go back into service by Friday.
The 41,000-tonne German-built super-ferry is capable of carrying 2,400 passengers and 650 cars. It went into service in 2004.