Lessons Learned – by Pat Carson

Lessons Learned


If you have an emergency on your vessel which communication device would you reach for first, your mobile phone or the VHF radio?

In Feb 1999, the Safety of Life at Sea (SOLAS) convention required all passenger ships to carry Digital Selective Calling (DSC) equipped radios, and in June of 1999 the Federal Communication Commission (FCC) required all VHF radios manufactured to be DSC-equipped. This effort started nearly a decade earlier due to the safety problems that lack of communications interoperability between SOLAS-regulated vessels such as cargo ships and other vessels such as recreational boats and commercial fishing vessels. The Coast Guard petitioned the FCC in 1992 to require all marine radios made or sold in the United States to have DSC capability. The Coast Guard had also asked the Radio Technical Commission for Maritime Services (RTCM) to develop a standard that would allow the incorporation of DSC in a marine radio without affecting the low-end market price of that radio. The FCC solicited comments on that petition in 1992 and 1993, and prepared a Notice of Proposed Rulemaking (NPRM) in early 1994. The FCC requested comments concerning that rulemaking from May to Nov 1995. Then on June 27, 1997, the FCC adopted a Report and Order (R&O) requiring radios that are to be type accepted on or after June 17, 1999 to include minimum DSC capability. If you have purchased a fixed VHF radio in the last 20 years, it has the little red button labeled distress.

What value is the distress button on your radio? Instead of taking time away from attending to an emergency on board your vessel to call for assistance, you can lift the red door, push the button, select your emergency from the list (fire, flooding, aground, medical, etc.) and push the button a second time. Your distress message is now sent digitally to all DSC-equipped radios within range, all law enforcement vessels and the USCG while you are attending to the emergency at hand. However, this only works if you have done two things, connected the VHF radio to your chart plotter or other source of GPS position data and programmed the unit with your Marine Mobile Set Identifier (MMSI). Connecting the radio to your chart plotter is as simple as connecting two wires, four if you want full functionality, or with most newer navigation electronics, plug the radio into your NEMA2000 backbone network. Several maufacturers have VHF radios that have their own internal GPS receiver and do not require an external source, eliminating the need for any external connection.


The Marine Mobile Set Identifier is the key to making the entire system function. If your radio is not programmed, then the DSC function and all the safety it offers is not available. Even though you still have a fully functional VHF radio, you will lack access to the modern features these radios have to offer.

All modern VHF radios manufactured after June 1999 will have the red DSC Emergency button. All other boaters will receive your DSC or voice distress call if they have programmed their equipment with the MMSI.

Obtaining an MMSI for domestic vessels is a simple process. If you do not plan to operate your vessel outside of the United States, you can obtain a no cost MMSI from BoatUS, www.boatus.com/mmsi, or from the United States Power Squadron (USPS), http://www.usps.org/php/mmsi/home.php. Plan on boating in Canada, Mexico, or other countries, then you will need to obtain your MMSI directly from the FCC. For vessels traveling to foreign ports, you will also need to have a ship’s station license and radio operator permit. For boat owners planning on travelling outside the United States, the MMSI is issued as part of the ship’s station license application process. More information on the FCC website at http://wireless.fcc.gov/services/index.htm?job=licensing&id=ship_stations. Under international treaties to which the U.S. is a party, you are required to have an FCC license to transmit your radio in a foreign port. It is recommended for Mexico, the Bahamas and Caribbean. BoatUS and the GMDSS Task Force are working to have the FCC lift the rule for Canada and the Bahamas, and the United States and Canadian Coast Guards are working together to respond to any distresses in the border waters.

Once you have been assigned a nine-digit MMSI, simply program the radio following the manufacturer’s instructions. After you enter the MMSI you become part of the system. Your radio constantly listens to VHF Channel 70 for a digital signal. If a signal is received, the radio will emit different tones for distress, urgency, safety, routine, position send, position receive and group calls. In the case of a distress call, the tone is loud and shrieking, and it will get yours as well as everyone else on your boat’s attention. Just touch any button on your radio to silence the tone and you will hear more about the nature of the call. If you have connected your radio to your chart plotter (remember those four wires) the coordinates of the vessel in distress will appear on your chart plotter. Modern navigation systems will even plot a course to the distressed vessel and display it.

VHF handhelds used in the United States should use the MMSI assigned to the ship to which the handheld is primarily associated, even if another radio on that ship uses the same MMSI. Noncommercial users of VHF handhelds not primarily associated with any single ship may use a different MMSI that is not provided to the FCC. VHF handhelds should not be used ashore.

Your cell phone has a limited range, prone to dropping calls in some areas, and is point to point with land based emergency services.

If your MMSI registration information or contact information changes for any reason, you must update your registration. If you sell your DSC-equipped radio, the AIS, or the boat to which these devices are mounted on, you must cancel your MMSI registration and should inform the new owner of the need to reregister the MMSI. This is necessary to ensure that the Coast Guard can contact the right persons if a distress situation were ever to occur. These registration changes can be accomplished by contacting the organization or agency which originally registered your MMSI. If you do not know which organization registered your MMSI, you can identify that organization by comparing your existing MMSI against those listed on the FCC website that shows the block of numbers issued by each third party, such as BoatUS or the USPS.

Do you wonder if your MMSI was issued by the FCC or a third party? If the MMSI ends with a zero, then it was issued by the FCC. If it ends with any other digit, then it was issued by an independent organization and is only valid for use in US waters.


Many of the new VHF radios are now capable of receiving AIS, Automatic Identification System information, and will display other vessels’ information on your connected Chartplotter. Check my May 2015 article on AIS for more detailed information on how this system is designed and the value it provides the recreational boater. When AIS information is displayed on a modern chart plotter, each ship “symbol” can reflect the actual size of the ship along with its position. By selecting a ship symbol, you can display the ship name, her course and speed, classification, call sign, registration number, MMSI and other information such as maneuvering information, Closest Point of Approach (CPA), Time to Closest Point of Approach (TCPA) and other navigation information more accurately and timely than information available from an Automatic RADAR Plotting Aid (ARPA) can be available. For a few dollars more, you can integrate an AIS transmitter on your recreational vessel and be seen by all commercial vessels and every AIS receive equipped recreational vessel.


The DSC system was designed such that the MMSI number was to stay with the vessel when sold and the information changed for the new owner. This is much like the vessel documentation where the documentation number stays with the vessel through all subsequent owners. To help enforce this policy, the equipment manufacturers designed into their AIS transmitters and VHF radios the ability for the user to program the MMSI once and in a few cases twice. After that, the radio must be deinstalled and sent back to the factory for a memory wipe and reprogramming. So even if you obtained a new MMSI you may not be able to program your existing equipment yourself. NOAA does not care; they will change your EPIRB registration pretty much anytime.

This screenshot of a modern GPS display with AIS shows all AIS transmit equipped vessels. The speed leader helps collision avoidance with their courses and speed indicated.

Rescue 21

The USCG National Distress and Response System Modernization Project updated the USCG VHF distress system to include DSC and direction finding capabilities and extends VHF radio coverage to 20 miles offshore. Rescue 21 has eliminated gaps in coastal coverage that the old system had. Rescue 21 reached initial operating capability in Dec 2005 full deployment was completed in Oct 2017. The system is now operational along the coasts of the contiguous United States, Hawaii, Puerto Rico, Guam, the U.S. Virgin Islands, the Northern Marianas Islands of Saipan, Tinian and Rota, parts of Alaska and in much of the Mississippi, Missouri and Ohio rivers and their major tributaries.

Should an emergency occur, you could use the DSC function of your radio to alert nearby vessels, law enforcement and the USCG without having to pick up the microphone and explain who you are, where you are, what is wrong and what assistance you require. According to industry sources, fewer than 10% of marine VHF radios have a working distress DSC button. Most VHF radio owners have not bothered to register for an MMSI number and enter it into their VHF radio, and have not connected it to a GPS signal on the boat. Of those 10% that have the MMSI entered, the USCG reports that approximately 90% of VHF DSC distress alerts received do not contain position information, and approximately 60% do not contain a registered identity. The Coast Guard cannot effectively respond to a DSC distress alert sent from such a radio.

Rescue21 has eliminated gaps in coastal coverage that the old system had. Rescue 21 reached initial operating capability in December 2005; full deployment was completed in October 2017.

As of March 2011, DSC-equipped VHF radios must meet more rigorous technical standards, one of which requires a Test Call feature, a simpler method of testing the DSC function. To run a test call on these latest generation of VHF radios, call the nationwide Coast Guard MMSI number, 003669999. Enter this number into your radio’s calling memory, select the test call option from the radio’s list of individual DSC calls and press the call key. Your radio will silently hail the Coast Guard with a digital signal on channel 70. If everything is working properly, your radio will almost immediately receive the Coast Guard’s acknowledgement of your call, providing assurance that both your radio and the Rescue 21 system are operating properly. The DSC function can also be used to communicate with a group of vessels. An example would be a club cruise where you would like to communicate with the flotilla. Consult your VHF radio manufacturer’s instructions as the process varies between the different radios.

I have heard the DSC distress siren only a few times, and it does indeed get your attention. In each instance the system worked as advertised, the alarm sounded, the position of the vessel in distress was displayed on my chart plotter and a course was set to their position. I have used the DSC group call feature several times when a group of us were on a Bay cruise. By entering a unique nine-digit MMSI into the memory, any one of the vessels could communicate with all vessels in the group by sending messages to all silently. I have never had to use the emergency DSC function, but I take some comfort knowing that the system is connected, operating properly and ready in case the worst occurs. As of 2015 the USCG has responded to more than 75,000 Rescue 21 initiated missions, proving the value of the system in taking the search out of Search & Rescue!

Lessons Learned

Connecting and programming your VHF radio and navigation equipment is much simpler than many of the instruction manuals make it look. A while back I was on a cigar and port friendly open flybridge assisting a client with connecting their VHF radio and chart plotter. While I connected the four wires, she was on the BoatUS website obtaining the MMSI. In less time than it takes to enjoy a fine cigar we had the system connected, programmed and a test message sent to the USCG.

Sending out a DSC distress call, information about the boat and her position is rapidly received by the USCG.

The majority of mariners know how to use the VHF radio. Dialing 911 on that mobile phone will get you to the highway patrol dispatch center, and then you need to try to describe your emergency and your exact location. Assuming your call does go through and does not get dropped as you are explaining the situation, you can only hope the operator knows something about the vast waterways of the San Francisco Bay and San Joaquin Delta. An emergency call on your VHF radio will not only be heard by other mariners in the area that may be close enough to lend assistance, but will also be heard by the USCG and other emergency services. To make an emergency call on the VHF radio, follow these guidelines:

Make certain the radio is turned on, is on channel 16 the international hailing and distress channel and is set to high power.

If loss of life is imminent, press the microphone button and say Mayday – Mayday – Mayday. Use Pan-Pan instead of Mayday if the situation is severe but not immediately life threatening.

Say your vessel name

  • Say your location – Latitude and Longitude or nearby navigation aids or landmarks, or the direction and distance to a prominent landmark.
  • State the nature of your distress.
  • State what assistance is required.
  • State how many persons are on board.
  • Estimate the severity of the emergency.
  • Describe your vessel – color, length, style, any other unique identifiers.
  • Release the microphone button and wait for an answer.
  • If no answer within 30 seconds repeat.

In an emergency, time is of the essence and you will want to get your message out to all stations as quickly and clearly as possible. Speak slowly, clearly and calmly, although that might be difficult if you have to attend to the emergency yourself while at the same time trying to get assistance.

Or, Press The DSC Button

The red button. Lift the door and press in an emergency.

When you sell your vessel or make a new purchase, do not forget to deregister the MMSI and then reregister with your correct information. All the other safety equipment on your vessel, EPIRB, SART, PLB etc. use the data that is registered with the MMSI. In an emergency, time is of the essence and delays can be fatal.

Until next month I am going to sit back, enjoy a fine port and cigars as I wait for my DSC-enabled navigation system to respond to a boater in distress. Until then please keep those letters coming. Even the ones where you slam me for my oversights.

Have a good story to tell, I love a good story. Have good photos of right and wrong, please send them and I will include them in next edition of “Is It Right Or Is It Wrong.” patcarson@yachtsmanmagazine.com

Modern vocabulary – acronyms used in this article.
How many do you know and use every day?

  • AIS
  • ARPA
  • CPA
  • FCC
  • GPS
  • NPRM
  • MMSI
  • NEMA2000
  • NOAA
  • PLB
  • R&O
  • RTCM
  • SART
  • TCPA
  • USCG
  • USPS
  • VHF