Its my understanding that all you need is a clear, unobstructed view of the southern sky. I'm pretty sure you won't have problems with obstructions on the open water. However, it still looks like you'll have to haul at minimum, your digital satelite receiver and some kind of dish with an LNB.
Its a whole lot easier if you own the boat. I don't think I would attempt it on a public cruise or some privately chartered trip. Take your laptop and a collection of dvds. You can do that easily without all the extra carry-on "luggage."