Critical Boating Electronics: DSC Radios

Knowing how to use a VHF radio, and of course having one on your boat in the first place, is a critical part of boating safety. Your VHF is the most important piece of boating electronics aboard because when it comes to calling for help it’s the most reliable form of communication, the Coast Guard monitors its airwaves continuously, and all VHF radios built since 1999 have been required to include Digital Selective Calling “DSC” functionality.

uscg rescue helicopter
If you need to call the US Coast Guard for assistance, nothing works faster than a VHF radio with DSC capability. Public domain photo courtesy of U.S. Coast Guard, by PO2 Brian McCrum.

My friend Lee came back from a boat show over a decade ago, and started asking me questions about VHF marine radios he’d seen there – ones with with “man-overboard” buttons. I explained that these radios, when hooked up to your GPS, could transmit a latitude and longitude when you push and hold the red emergency “SOS” button. And that was for any emergency, not just MOB situations. It led to a broader discussion about how these radios actually work.

DSC has two forms: Category A for commercial shipping and Category D for recreational boaters. Both category A and D radios can send and receive digitally encoded distress calls on Channel 70, which is reserved exclusively for emergency digital communications. Category A radios have more features and are much more expensive.  For the purpose of this blog, we’ll be discussing type D or recreational DSC.

VHF radios equipped with DSC are capable of transmitting a distress call that includes your position if your radio is connected to your GPS or has its own internal GPS receiver (as is the case with many modern units). It can also automatically transmit vessel particulars such as type of boat, size, and so on, provided you register your radio (which is free) with the maritime mobile service. All VHF DSC radios have a unique ID number called the MMSI and after registering, when you send a distress call, your radio’s ID is matched to the database of information. Rescuers can be on their way with your position, vessel particulars, and emergency contact info in hand just as soon as you’ve hit that SOS button. The registration also helps the Coast Guard identify false alarms.

vhf radio with dsc
During a recent refit this boat had a DSC radio with internal GPS added. Flip the red cover off the SOS button, press and hold it, and your emergency call goes out to the USCG including GPS position data. Photo by Lenny Rudow.

To send for help, all you or one of your crew needs to do is manually lift the red protective cover, then push and hold the emergency button on your radio for a few seconds. The transmission will continue automatically until manually shut off or the power fails.

dsc button an a vhf radio handset
On some radios, the SOS button may be located on the handset. Photo by Lenny Rudow.

For my friend Lee and other boaters, nothing beats a VHF with DSC when calling for help. Sure, we all have cell phones aboard these days. But batteries die, calls get dropped, cell connections can get sketchy at sea, and range can be very limited in some areas. Yes, you may also want to have emergency signaling devices such as satellite messengers or EPIRBs aboard. No matter how you look at it, however, the DSC VHF radio is your first and best way to call for help in a hurry.

vhf radio at the helm
Yes, we all have a cell phone aboard these days. But a VHF with DSC is a far more reliable way to call for help. Photo by Lenny Rudow.

Even though DSC has now been around for decades, according to USCG statistics there’s still a big problem in making sure they’re active and registered, and only about 10 percent of recreational boaters take this simple but critical step. Ensuring the radio has a GPS signal is easiest if you just buy a radio that has internal GPS. But if yours does not, turn it on and look at the screen to see if it displays GPS coordinates and/or a satellite icon. If not, you’ll need to connect your chartplotter’s NMEA out wire with the VHF’s NMEA in wire (you may also need to connect a ground wire). If the wires aren’t marked, color-coding can be determined by looking at the VHF manufacturer’s owners or installation manual. Then you can program in your MMSI number, and the system is ready to roll.

Okay: you have your DSC VHF radio all set, but you’re wondering about what other critical boating safety issues you need to be aware of? Check out out Boat Safety Guide for more information.

Editor’s Note: This article was originally written in 2013 and was last updated in July of 2022.