Do what James says, sign up for DirecTV, BUT just get one receiver (if
your
using cable at home). You can even go so far as having the free install
done
so the receiver is activated. Then just put it on your boat with the
portable dish.

The only downside to using your home account on a boat is if you travel
outside of your home area. Local programming is delivered via 'spot'
satellite signals. If you travel more then about 100 miles from the local
coverage area you won't be able to get your local stations. As in, your
account is listed as a Boston address and you take the boat to Florida.
You'll get neither the Boston locals nor the Florida ones. The receiver's
only setup, via programming, to deliver the Boston locals and you'd be well
out of the coverage area. I do not know if the mobile system has a way
around this. There are ways to work with DirecTV to get 'out of market'
programming, so call them and ask if it really turns out to be necessary.