There is mension of tilt alarm in config but I've never come across 1 or seen any other reference to it and don't recall it in the diagrams plus I'd expect it would be something like 35-45 degrees tilt.
I'm not aware of any other sensors eg shock sensor etc.
Factory cat 1 alarm consists of the battery backup sounder and bonnet switch and interior combined lights and ultrasonic sensors.
So 99.99% no it won't go off on a ferry.
Unless!
There is interference by the ultrasonic sensors, very unlikely but there used to be some instances in my mk5 escort days where open air vents may interfere but that's improbable i guess.
Or the motion is enough to wobble a door that affects the mechanism enough to send a signal to the bcm for central locking system. Also improbable and unlikely.
Next there's Act of God..............
56 350 2.2 130ps mk7 with 2 side doors
65 290 2.2 125ps custom with 2 side doors
07 350 170ps
Ids v86 licence + v86.04 update + xprog
hereIds map
here