Use Your VHF-DSC Radio with Confidence

Tony Gardiner, director, United Safe Boating Institute

Marine VHF radios with Digital Selective Calling (DSC) are part of a worldwide upgrade of maritime communications. They allow boaters to make ship-to-ship private calls to other vessels equipped with a VHF-DSC radio, and in emergency situations they allow boaters to send an automatic mayday at the touch of a button over marine Channel 70, which is monitored by the U.S. Coast Guard and large commercial vessels.

To work properly, however, VHF-DSC radios must be registered and encoded with a unique nine-digit Federal Communications Commission (FCC) identification number — called a Maritime Mobile Service Identity (MMSI) — that functions much like a telephone number. Once the radio is properly registered through the FCC or its designees — BoatU.S., Sea Tow or the United States Power Squadrons — the MMSI number and identifying information about your boat are entered into the U.S. Coast Guard’s national distress database.

The first three digits of the nine-digit MMSI number denote the geographical area and are followed by six digits. In the United States and its territories, the geographical area begins with the number 3 (i.e., 3XX, with the Xs assigned any digit from 1 to 9). Group MMSIs start with the number 0, immediately followed by the three-digit geographical code, plus five more digits.

There’s one more step. To take full advantage of the VHF-DSC radio’s ability to send an automatic mayday, you need to connect your radio to a GPS that can transmit your vessel’s location and its identifying information. Properly connected and registered, your DSC radio will transmit your position and, if entered, the nature of your distress to rescue authorities. (If you have a GPS that is not connected to your radio, you can still enter your position manually.) Once activated, your DSC radio will continue to transmit your emergency signal until it is acknowledged.

If you obtain your marine VHF-DSC radio through a dealer or during a new-vessel purchase, make sure you apply for your MMSI number immediately. As part of the application process, you will be asked to provide your name, address, telephone numbers (yours plus an emergency contact) and the vessel description, including registration number, vessel type, length and passenger capacity. Should you need to activate a distress call later, this information, embedded in your MMSI, will be provided to the nearest Rescue Coordination Center (RCC), ensuring that no matter where you are in the world, local authorities will have an excellent chance of finding you and rendering assistance or rescue.

If you purchased a secondhand boat with a VHF-DSC radio already installed, take the radio to a recognized marine electronics store and have the old MMSI replaced with your new MMSI. Before heading out on the water, take time to input the MMSI numbers of vessels with which you’re likely to have contact in your radio directory. If you belong to a yacht club, Power Squadron or other boating group, chances are that they will have what is known as a Group MMSI, which will let you alert all other members of the group at once. This is useful for cruises and other on-the-water activities, but emergency situations are where it really comes in handy.


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