I went from Devonport back to the Australian mainland, to Melbourne, by ferry, the Spirit of Tasmania, it is big boat that has some nice entertainment shows, I even got invited to sing a long with the performing start of the evening...
The ship from Melbourne to Devonport leaves from Station Pier, on Port Phillip Bay.
Normally crossings are overnight, but during the high season, an extra ship has been put on weekend crossings so there is the option of a day crossing too.
We tried it both ways and enjoyed them equally.
We paid about $200 each for the night crossing in a cabin with no porthole (cars presently travel free).
And $100 each on the way back, day crossing sitting up, non allocated seating.
Night crossings are allocated seating (but if you’re lucky you may be able to find a more comfortable spot to stretch out in in one of the lounge areas)
Good facilities on board - restaurant, cafes, bistros, souvenir shops, bars, even pokie gambling machine room, mini children’s playground.
Bonus : it’s very easy to book online and pay by c/c and just pick up your tickets while you’re waiting at the pier in the often long boarding queues.