USCG Safety Alert Concerning DSC-equipped VHFs

Is your DSC-capable VHF properly set up?

Standard Horizon VHFs


Most of today’s fixed VHF marine radios come equipped with Digital Selective Calling (DSC) capability, and many high-end handheld VHFs do as well. For years, Practical Sailor has recommend that buyers select a DSC-equipped model with this capability—and for good reason: As the U.S. Coast Guard’s new marine radio network Rescue 21 becomes operational throughout the U.S., rescue centers are able to receive instant distress alerts from DSC-capable VHF radios. However, spending the extra money to have a feature-loaded, DSC-capable VHF offers little benefit if you do not have the radio properly registered and set up.

The Coast Guard recently issued a safety alert, warning that mariners were endangering their lives and those of their crew by having a DSC-capable VHF that lacks identifying information. According to the notice, about 90 percent of VHF DSC distress alerts received by the Coast Guard do not contain position information, and approximately 60 percent lack a registered Maritime Mobile Installation Identity (MMSI) number. Without this information, the Coast Guard cannot effectively respond to a DSC distress alert.

In fact, search-and-rescue efforts may normally be suspended when no communication can be established with the distressed boat, no further information or means of contacting the boat can be obtained from other sources, and no position information is known.

The steps involved in properly setting up DSC-capable electronics—obtaining an MMSI, entering it into the device, and interfacing it with a GPS—are fairly simple. But not taking the steps is essentially like buying a life raft and then leaving it at the dock.

If you have a VHF with DSC function, be sure you have all of the possible data input and that it is up to date, and if possible, link it to your GPS so that search-and-rescue operators will have your location information.

Here’s a rundown on how to get an MMSI, along with the answers to some frequently asked questions we receive regarding DSC. (More information can be found at the Coast Guard’s Navigation Center website,

  • What is DSC? DSC’s foremost purpose is distress alerting. With the press of a button, users can send a pre-configured distress message to emergency personnel and other DSC-equipped boats in range. The digital message is sent over channel 70 and contains pertinent information about the boat, its Maritime Mobile Service Identity (MMSI) number, owner details, and emergency contact information. When a DSC radio is connected to a GPS, the Mayday includes the boat’s location. The transmission takes about one-third of a second and is automatically repeated until a rescue authority answers. Because the signal is digital, it has a better chance than a voice call of getting through in rough conditions.

A DSC transmission includes the priority of the call (distress, urgency, safety, routine), who the call is being sent to (all ships or a specific ship/station), and the transmitting boat’s identity, location, and nature of distress. DSC also allows sailors to use their VHF radios like a cell phone for ship-to-ship and ship-to-shore communications, without interfering with VHF hailing traffic and without the limitations and cost of cell coverage.

  • What is an MMSI number? All boats operating on the high seas are assigned one nine-digit MMSI for all onboard equipment capable of transmitting and receiving digital signals—including EPIRBs, AIS transponders, DSC-capable VHFs, all INMARSAT satellite terminals, etc.—and that number serves as an identifier for the boat. Once a boat owner registers the vessel with the appropriate agency (the Federal Communications Commission in the U.S.), the boat’s emergency contact information is linked to the MMSI number, which is then programmed into the onboard electronics. When a distress call is broadcast, the MMSI is included in the message, giving rescue and emergency personnel accurate details of the boat.
  • How do I get an MMSI? For recreational boats operating in U.S. waters, boat owners can attain an MMSI through the FCC (888-225-5322, or another approved agency, such as BoatUS (800/563-1536,, Sea Tow (800-4SEATOW,, or the US Power Squadrons ( However, all U.S. flagged commercial boats and those recreational boats operating in international waters must get their MMSI license directly from the FCC. If you think your boat may ever be sailing international waters, we suggest getting your MMSI from the FCC. Otherwise, a new MMSI will have to be attained from the FCC and entered into all onboard digital electronics before leaving U.S. waters.
  • How do I interface my GPS and DSC-equipped GPS? Instructions should be provided in the radio and GPS operators manuals. Use a two-wire NMEA 0183 interface on all DSC-equipped marine radios and on most GPS receivers.
Practical Sailor has been independently testing and reporting on marine products for serious sailors for more than 45 years. Supported entirely by subscribers, Practical Sailor accepts no advertising or any form of compensation from manufacturers whose products we test. Testing is carried out by a team of experts from a wide range of fields including marine electronics, marine safety, marine surveying, sailboat rigging, sailmaking, engineering, ocean sailing, sailboat racing, and sailboat construction and design. This diversity of expertise allows us to carry out in-depth, objective evaluation of virtually every product available to serious sailors. Practical Sailor is edited by Darrell Nicholson, a long-time liveaboard sailor and trans-Pacific cruiser with more than three decades of experience as a marine writer, photographer, boat captain, and product tester. Before taking on the editor’s position at Practical Sailor, Darrell was the editor of Offshore magazine, a boating-lifestyle magazine serving the New England area. Darrell has won multiple awards from Boating Writer’s International, including the Monk Farnham award for editorial excellence. He holds a U.S. Coast Guard 100-ton Master license and has worked as a harbor pilot and skippered a variety of commercial charter boats.


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