I believe these might be the Disney Cruise Liner ships. Look on google.
DCL has two ships: Sorcerer Mickey stands at the bow of the Disney Magic; the bow of the Disney Wonder has Steamboat Willie. The stern of the Disney Magic has Goofy painting, while Donald Duck and his nephew Huey are painting the stern of the Disney Wonder. The statues in the lobby of each ship are different: Helmsman Mickey in the Disney Magic and Ariel from Disney's "The Little Mermaid" in the Disney Wonder.
Don't think it was a Disney, I'm sure Tweety Pie and Taz (amongst others) were painted on the side. Don't even think it was a cruise ship now, come to think of it. I remember it featured on the DVD of the cruise that I bought, so I'll check it out when I get home and post the answer here, if I find out.
The ship in question is a ferry called moba.
I have seen this also and I seem to remember it was the local ferr.
Might be one of the aida line which do have cartoon style paintings on sid.
If you were in Civitavecchia, then it would have been the MOBY Line vessel 'Moby Aki.
The ships with the Looney toons cartoons along side are from MOBYLINES please visit mobylines.it or mobylines.de ther you will find more picture.