Where is this 2nd dish mounted? If it is on the boat itself you will not be able to use it for satellite TV even while tied to a dock. There is simply too much movement on board to get an antenna pointed and maintain that connection. If you are putting the antenna on a beach and running the coax to the boat that will work just fine. Just let us know a bit more about what you are trying to do.
It's also possible that you are referring to a dome style antenna mounted on board your boat. It must be an in-motion dome (capable of reception while moving) for the same reasons mentioned above. Let us know what kind of antenna and where it will be located and any additional information you can think of.
What I post is my 2 cents and nothing more. Please don't read anything into my post that's not there. If you disagree, that's OK.
Can't we all just get along?