DirecTv has a boat setup. Heck it is even on sale right now.
http://www.boatersland.com/kvhm3st.html
or you can do what I did. I bought something like this...
http://www.cnet.com/4520-10602_1-5618415-1.html
Mine is a 26" Sony. Great picture.
Unless your in a great spot on the water you won't get much over the air HD. You need a pretty high antennae to get anything. Even in a house up here.
I tape shows and movies during the week, making sure I don't watch them until I am on the boat.....


Walmart always has the 'ol DVD bin with DVDs for $5.00. I stock up on a few of those too. Mainly I just relax, have a few drinks and pass out anyway....