Making a Mayday Call on Marine SSB Radio


For more than a decade, the Digital Selective Calling (DSC) distress call has been the digital-age equivalent of the familiar Mayday call and the preferred means of making initial contact with rescue agencies in the U.S. and around the world.

DSC allows users to make a distress call by pushing a dedicated red button on the front panel of an SSB radio. Instantly sending rescue agencies your boats identity, GPS location and more, the DSC distress call is at heart of the Global Marine Distress and Safety System.

In order to take advantage of the DSC function, youll need to have your SSB interfaced with a GPS and have a registered Maritime Mobile Service Identity number (MMSI). To get an MMSI number, a U.S.-flagged vessel will need to obtain a Ship Radio Station License from the Federal Communication Commission (FCC) by submitting FCC License Form 605. This is a requirement for all U.S.-flagged boats that operate a single-sideband radio.

Even though you may already have an MMSI number for your VHF through a BoatUS or SEA TOW vendor, that number is not valid for use with a marine single-sideband radios. You will need to get a new number for existing equipment by completing Schedule B along with your FCC License Form 605. The new MMSI will be coded for international waters and the registration will be entered into the International Search and Rescue database. This is the number you should program into all applicable radio equipment on board (a list of this equipment appears in Schedule B). If you have a used SSB radio that a previous owner has programmed with an MMSI, you will likely need a dealers help to reprogram it with your MMSI number.

In addition to programming the MMSI number in the marine SSB, you also need to supply it with GPS data. Usually, there is a jack on the rear of the transceiver for this connection. Next, you need to add a dedicated DSC HF receive-only antenna to the empty antenna jack, usually on the back of the radio. Fortunately, this receive-only antenna is inexpensive and fairly simple to install.

Incoming DSC signals are usually very strong, so almost any external coax-fed wire antenna will work well. One step up from a simple wire is the popular proven is the Metz DSC Receive / WeFax antenna, secured to the stern rail. This keeps the antenna as far away from sources of interference as possible, allowing for the best overall HF receive performance in a simple, inexpensive antenna.


The U.S. Coast Guards long-range communication facilities guard four marine single-sideband frequencies for distress calls, although that coverage is not simultaneous, nor is it 24/7. The station names, frequencies, and times (universal time) that each station monitors are listed above.

If you do not have a DSC-equipped radio and are making a voice distress call, you should be familiar with these frequencies and times. Remember, although the U.S. Coast Guard maintains a voice watch on these frequencies, they are no longer being monitored for voice traffic in most parts of the world (another good reason to enable the DSC function). It is also important to note that as of Aug. 1, 2013, the U. S. Coast Guard terminated its radio guard of the international voice distress, safety, and calling frequency 2182 kHz and the international DSC distress and safety frequency 2187.5 kHz.

A link to the USCGs safety alert detailing this new change, along with other important information on making a DSC distress call, can be found on the Inside Practical Sailor blog Making a DSC Mayday Call, posted on Oct. 24, 2014. The blog also links to a video posted by PS reader John MacDougall, a radio engineer and systems designer with 40 years experience; the video covers the steps required for enabling DSC and making a DSC call.

U.S. Coast Guard Marine HF Radio Monitoring Stations
Making a Mayday Call on Marine SSB Radio
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