receive and resend wifi

I have a question about setting up a network on a boat. We are alot of ppl and everyone has a macbook or macbook pro plus there is an AppleTV on the boat. All the marinas have wireless that you pay for. What we always do is one person receives and pays for the wireless on their macbook, then sends the signal to another macbook through ethernet and that person then resends the signal wirelessly so everyone can use it. This is very annoying and complicated plus the signal that the macbooks send out isnt very strong. I am trying to figure out a permanent solution but don't know much about wifi. I want a way of picking up that signal and making the boat have its own network that everyone can connect to. How do I do that?