What’s the number-one reason why the Coast Guard can’t find boaters, even though they have DSC equipped VHF radios on board? Because the radio wasn’t properly interfaced with their chartplotter. In fact, according to the Coast Guard even though all VHFS sold in the US are required by law to have DSC functionality, 90-percent of the boats with both GPS and VHF units on board don’t have them properly hitched.
This is a serious problem, since DSC – which gives the Coast Guard your exact location and identity automatically, when you make a Mayday call - could save your life in an emergency. So why don’t people make sure their radio and their GPS are communicating with each other? Often, because interfacing electronics seems like a daunting task. But it shouldn’t; the units talk the same language thanks to NMEA0183 and/or NMEA2000 standardization, and interfacing them takes just two wiring connections: an NMEA data in/out wire, and a ground wire.
Unfortunately there’s no standard color-coding for these wires. That means you’ll have to refer to your owner’s manuals to find out which wire is which. You can’t find that manual? No problem – a quick Google search almost always solves the problem. Once you know which wire is for data and which is for the ground, merely crimp them together using butt connectors, and protect the connections with adhesive-lined heat-shrink tubing and/or liquid electrical tape.
To make sure your units are communicating, turn both of them on and look at the VHF’s screen. If it displays GPS coordinates you’ll know you’re good. Some other units have a small satellite icon that appears, to let you know the data is flowing. If it the interface doesn’t seem to be working properly, before you check your wiring connections scroll through your GPS unit’s menu. Some units don’t put out the NMEA data stream unless you check a box or choose to activate it. (Again, a Google search will usually tell you if this is a necessary step). Once you think you have it working, you can verify it’s active by placing a radio check call to TowBoatUS, which has a free DSC radio-check call service.