The journey over to Devonport from Port Melbourne on the Spirit of Tasmania is a great experience. We took our car, and found the experience to be enjoyable, however it was quite a rough journey over. It was completely different on the way back. The weather can be unpredictable, so my advice would be to perhaps take some seasick tablets in case you start to feel unwell. There are a lot of bars and restaurants to go and there is a cinema on deck. My tip would be to perhaps take a small bag on board as its difficult to lug a large suit case up the stairs on the boat.