OK, here's a schematic. I agonized over the voltage regulator. The counter datasheet says it draws 500mA, and with the boat's battery at 14V (charging), the maximum dissipation of the 7805 will be 4.5W. However, I'm sure that's with all 28 LED segments lit. Normally, that will never happen. Still, you should have a husky heat sink on it. I considered specifying a switching regulator, which would be much more efficient, but a canned one is harder for me to find (maybe one of the other guys knows of one), and I didn't want to design one. If you go with the 7805, I'm still not sure of a part number for the heat sink. Again, maybe one of the other guys can chime in.