As part of the gradual replacement of outdated systems on our Norlin 34 project boat, it was time to look at communications. As any radio manufacturer will tell you, the problem with VHF radios is twofold: they are inherently reliable, thus tend to be a long way down the list of essential upgrades for owners of older boats. As long as you can use Channel 16 in an emergency or call your launch service or marina, what else matters?

Quite a bit, actually, especially if you plan on doing some extended coastal or offshore cruising. Cell phones and smart phones can be very useful, but don’t make the mistake of thinking they can take the place of a VHF radio, especially one equipped with Digital Selective Calling (DSC). All fixed-mount VHFs sold these days are DSC-compatible, enabling them to work somewhat like a telephone in that you can direct-dial other DSC-equipped vessels or shore stations or, at the push of a button, send an automated digital distress signal that includes your position and the details of your boat. This facility is contingent on two things: that you have acquired a Marine Mobile Service Identity (MMSI) number, and that you have linked your new radio to a GPS receiver.

Commercial shipping is required by law to carry DSC radios, but we lucky leisure-boat sailors are not. Still, I like the safety aspect of DSC radios; in a genuine emergency I would rather be able to push a button than sit shouting “Mayday” into a microphone while all hell breaks loose around me.

All of this sounded like a good idea, so I decided to deep-six our ancient (though still serviceable) Standard Horizon radio and replace it with a DSC-capable unit. You can buy a fixed-mount radio for under $100, so this is hardly an upgrade that’s going to break the bank. But I also wanted to install a remote microphone in the cockpit. These are invaluable when you’re alone on deck. This restricted the choice to Standard Horizon or Icom, both of which make excellent radios with remote-control microphone options. My choice was Standard Horizon’s Matrix GX3000S and the CMP 25w RAM+ microphone. It puts all the essential VHF functions at the helmsman’s fingertips, including WX channels and a well-protected DSC distress button. Like the fixed radio, the RAM+ is waterproof.

Replacing a VHF radio is a fairly straightforward affair, provided the new unit fits in the same space as the old one. All you do is take the radio out, unplug the coax antenna and power supply, and hook up the new unit in its place. However, I would have to connect together the radio and my Navman chartplotter, which meant entering the murky world of NMEA 0183 protocols. Considering that I know next to nothing about hooking up things that go beep, this was a tall order for me. Still, nothing ventured, nothing gained…

1. The old and the new. The Matrix GX3000S is considerably larger than the old radio it replaces, so I have to enlarge the aperture it will go into. Fortunately, there will still be room for the larger fascia between the plotter and the stereo

2. I’ve opened out the mounting hole and connected the antenna (left) and power feed (right). In the center is the RAM+ cable, which I hooked up just for the sake of it. It actually has to be fed in from the cockpit because of the size of the terminal at the other end. The two bundled-up black wires at right are for a loud-hailer speaker, which I decided not to install. The third black cable is the NMEA connection

3. Now it was time to make the GPS talk to the plotter (see sidebar). You would think there would be a common protocol for wire colors, but that is too logical. Each manufacturer uses different colors for its + and – in and out wires. After consulting both manuals, I figured out the correct combination of wires and joined them together in this low-tech connector. It was meant to be temporary; two years later it’s still there (ahem)

4. Time to switch on the radio and see if everything works. Yes! The satellite icon at the top right of the screen shows the radio is receiving GPS data from the plotter

5. With the plotter and radio talking to each other, the next step was to enter the MMSI number into the radio

6. Time to install the Ram+ unit. It comes with 20ft of cable, which should be ample for all but the biggest boats. I decided to place the connector socket under the main traveler where it is unlikely to get in the way of the crew working in the cockpit

7. Because of the size of the connector, I had to drill a 7/8in hole for the cable. It looked huge: you’d better be really sure you want that hole in that particular place before you start drilling!

8. I’ve run the cable through to the radio, drilled the pilot holes for the fixing screws (always slightly undersize in fiberglass), and gooped up the fitting to keep water out

9. A nice flush fit

10. I spent a couple of hours routing the cable under and through various parts of the boat before I could connect it to the radio

11. All hooked up and ready go: power’s on and it works!

12. Now I’ll be able to talk to other vessels without leaving the helm, and won’t have to rely on the handheld VHF with its short battery life. Note that in the timespan between acquiring this unit and completing the installation, both the Matrix GX3000S and RAM+ microphone were superseded by newer models. The installation procedure will be exactly the same

You and your MMSI

The Maritime Mobile Service Identity is a unique 9-digit number that’s assigned to your boat, not you. It is programmed into all digital transceiving equipment on board—VHF and MF/HF radios, AIS transceiver—and it stays with the boat when you sell it.

If you plan only to sail within U.S. waters, you can apply for an MMSI through Boat US, the US Power Squadron, or even Seatow. These numbers are loaded into the Coast Guard search and rescue database. If you want to take your boat out of the country, you should apply for a MMSI through the Federal Communications Commission (FCC); in order to do that, you’ll also have to cough up for a Ship Station License. FCC-provided MMSI numbers are put into an international search and rescue database.

On the application form, you’ll be asked to enter your name, contact details, vessel details and description, and names of contacts ashore.

Talkers and Listeners

My task was to make the Standard Horizon VHF radio and Navman plotter communicate with each other via a basic NMEA 0183 connection. NMEA sends data between a transmitter (Talker) and a receiver (Listener). In this case, where we wanted the GPS to send position data to the radio, the plotter is the Talker and the VHF is the Listener.

Sounds straightforward, right? It is, until you see all the wires you have to make sense of. The VHF only had two that concerned me: NMEA – IN and NMEA + IN. These were the Listeners. I had to find the chartplotter’s Talkers—the NMEA – OUT and NMEA + OUT wires. I found these by consulting the manuals for each unit. I found that the plotter’s NMEA – OUT (Talker) wire was black (also serving as the 12V negative) and its NMEA + OUT (Talker wire) was white, and that the radio’s NMEA + IN (Listener) wire was blue, the NMEA – IN (Listener) wire was green. It turned out that I only needed to connect the blue wire and the white wire together. The other white wire seen in Photo 3 is the NMEA + IN for the Tacktick instrument system, which can display GPS data. The red wires are 12V power feeds, and I connected the black NMEA – OUT/negative wire from the plotter to the black negative wire from the radio.

Life would be much simpler if there were a common protocol for all these wires, but that obviously makes too much sense!