I thought it was going to be a case of singing, "I saw saw three ships come sailing in" four times, but I stopped when I saw only 11 boats. Maybe some would pass as ships.
I love the style of the artist, Tiphanie Beeke, so I looked her up. She's a British artist living in the south of France and has illustrated a number of children's books, winning several awards in the process. Some of her illustrations are published as postcards by Nouvelles Images - including this one where the title is Twelve Boats. Could they be charged under the Trade Descriptions Act?
On Christmas Day, on Christmas Day;
I saw three ships come sailing in
On Christmas Day in the morning.