Register Your VHF Radio


The U.S. Coast Guard continues be concerned about the misuse (or lack of use) of VHF radios for distress calling. Many boaters, it seems, don’t understand the importance of registering their radio equipment, and how to properly use Digital Selective Calling (DSC) feature. Here we offer a brief overview of the most frequently asked questions regarding DSC. More information can be found at the Coast Guards Navigation Center website,

WHAT IS DSC? DSCs 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 boats 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 boats 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 boats 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.

The FCC and Coast Guard strongly encourage all boats to apply for an MMSI to enable DSC use in the case of an emergency. With the Coast Guards VHF-based Rescue 21 vessel ID system adding more and more stations, having the ability to send a DSC distress call will greatly increase a boaters chances of rescue.

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,, or the US Power Squadrons, radios registered through Sea Tow can still be managed through its website (Sea Tow (800-4SEATOW, However, all U.S. flagged commercial boats and those recreational boats operating in international waters must get their MMSI license directly from the FCC. You can start the process online by filing FCC Forms 159 ( and 605 ( 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.

Darrell Nicholson
Practical Sailor has been independently testing and reporting on sailboats and sailing gear for more than 50 years. Supported entirely by subscribers, Practical Sailor accepts no advertising. Its independent tests are carried out by experienced sailors and marine industry professionals dedicated to providing objective evaluation and reporting about boats, gear, and the skills required to cross oceans. Practical Sailor is edited by Darrell Nicholson, a long-time liveaboard sailor and trans-Pacific cruiser who has been director of Belvoir Media Group's marine division since 2005. He holds a U.S. Coast Guard 100-ton Master license, has logged tens of thousands of miles in three oceans, and has skippered everything from pilot boats to day charter cats. His weekly blog Inside Practical Sailor offers an inside look at current research and gear tests at Practical Sailor, while his award-winning column,"Rhumb Lines," tracks boating trends and reflects upon the sailing life. He sails a Sparkman & Stephens-designed Yankee 30 out of St. Petersburg, Florida. You can reach him by email at


  1. i have a hand held VHF radio with DSC capability. it came with a preassigned/preprogammed MMSI number. i also just acquired a MOB1, an AIS Man Overboard Device, which also has a preassigned/preprogrammed MMSI number. is this number given when registering the MMSI number with BoatUS? your article implies that MMSI numbers are always issued to applicants and applied to specific boats. can they also be connected with handheld VHF radios and personal AIW Man Overboard Devices?