Heres how I would test it.
I would get about 40 feet of rope, tie it securly around the cabinet and use the handset cords to tie the phones to the same rope. This will give you good connection from the cabinet to the phones. Now tie the other end of the rope to the front of your boat and you know the rest. [Linked Image from sundance-communications.com]
No really look for manuals (try the Tab above) and jump right in get you hands dirty. Good luck with your new toys.