Type the name of the marina + WiFi into google. This should bring up the details, like this one for Hartlepool. click here
This should give you the rates and details of where to apply. They should then give you a password key, when you have paid.
Just right click on the WiFi icon in the system tray. View available wireless networks. Pick the network and enter the password key and away you go.
You should not need any special software.