the departure time is 1930,what is the arrival time, is it a car ferry, and does it have sleeping quarters?
Well... that would be nice to know which Company you use...
But if we suppose it's Stella Line, it arrives at 7:30 the next morning.
If it's overnight Ferry, it's sure there are sleeping quarters, the boat is "Stena Saga",
http://www.stenaline.no/ferge/vare-skip/stena-saga/
(My norwegien isn't very good, but if I understood well, you can find cabins under "lugarer" on the right side, and there are room for a pony.. for 510 cars.. so maybe for yours too)