They do this on the ferry ride from Rotterdam to Hull as well. I think the ferry just goes really really slow to make sure it arrives at 7am. I bet they save on fuel doing this as well.

If you ever want to go between Britain and The Netherlands this has to be the most relaxing way to travel. Get on the boat around dinner, eat dinner on the boat, have a beer, go to your room and sleep, wake up in your destination.

It's even better than night trains.