Coastal Boating, Sailing, Cruising, Yachting, Racing, Coastal, Sailboat, Yacht, Fleet, Club, Regatta, Commodore, One design, Social, Long Island Sound, Narragansett Bay, Buzzards Bay, Chesapeake Bay, Island, Seamanship, NE waters, NOAA, NWS


VHF Radio Basics

Related Stories

You just bought a new VHF radio with DSC. 

Now, install it properly to get all the safety benefits it offers!

So you installed a snazzy new radio with Digital Selective Calling (DSC).  It’s that little button behind the protective red shield.  You know it’s a great emergency feature that will keep you safe in coastal waters without an EPIRB.  But if you haven’t programmed in a Maritime Mobile Service Identity (MMSI), you haven’t done enough. 

Let me explain.  Marine radios equipped with DSC serve as one facet of the Global Maritime Distress & Safety System (GMDSS), which represents a major overhaul of the international system governing safety radio equipment and procedure on commercial ships. While recreational boaters are not required to participate in GMDSS, it makes sense to take advantage of the improved telecommunications for safety reasons.  Not only does it aid in rapid deployment of assistance now, in the future commercial vessels will no longer be required to monitor channel 16 so it will be the primary means of communicating with others in your vicinity in an emergency if you do not have an EPIRB. Channel 70 has been designated the VHF/DSC digital call channel.

DSC technology allows boaters to send a digital call directly to other DSC-equipped vessels and shore stations, somewhat like a telephone call. Once the DSC call has been confirmed, both parties are automatically switched to a working voice channel. If properly installed, one push of a button in an emergency, and your DSC radio will send an automated digital distress alert consisting of your MMSI identification number (if it was input), and position (if it is interfaced with a GPS receiver) to other DSC-equipped vessels and search & rescue facilities.  When they respond, they will automatically be connected to whatever channel your radio is set to. Of course, if you haven't interfaced it with your GPS and MMSI number, the only thing you will do is send an alarm. Ships around you won't know who it's coming from nor where you are.

One other nifty feature is that your MMSI number can act as a direct homing device to other similarly equipped radios that have your number.  It’s a like a VHF phone number.  You program in your friend’s MMSI and that radio is automatically and directly called without having to hail them on a public frequency.  Of course, as soon as they answer, they will connect with you on the radio frequency you are standing by on, so keep in mind it’s still a public channel.  Make sure you are standing by on a working channel not on a reserved frequency like channel 16 (see radio basics for more information on VHF radio etiquette).

Obtaining an MMSI number is free and easy if you are planning to cruise only in US waters.  It’s obtainable online, by mail, or by fax by registering on the BOAT US website or by downloading their printable form. They’ve been authorized by the US Coast Guard and FCC to act as an intermediary FOR VESSELS NOT REQUIRED TO HAVE A VHF RADIO LICENSE.  Click here for more information.

Otherwise, it can be a bit more complicated because you’ll have to fill out FCC registration forms and pay for processing.  If you are applying for a VHF radio license anyway (not required in US territorial waters but a must when you leave the states for a cruise to Canada, Mexico and beyond), be sure to request an MMSI number whether or not you currently have a DSC capable radio.  You’ll have the code available for when you upgrade your equipment and you won’t have to apply twice (and potentially pay twice).  Be advised that the FCC assigned number is listed in the International Search and Rescue (SAR) database while the Boat US assigned number is only listed in the USCG SAR database.  If you are planning international travel, you must get the FCC assigned number. We'll be providing information in a separate article on how to apply for a ship's radiostation license because it's just a bit too much to cover here.

Follow the manufacturer’s instructions about how to input the MMSI and link to the GPS.  Please note that some manufacturers limit the number of times (typically two) you can try to program your MMSI number into the radio. If you try too many times, the radio may lock out future attempts, forcing you to send the unit to the manufacturer to re-program it. So it pays to be careful the first time around.

DSC VHF radios DO:

  • Have one touch emergency capability that sends out a vessel's unique MMSI number and, if properly connected to a GPS, the vessel's position in latitude and longitude coordinates.
  • Allow for an inexperienced crew member who is unfamiliar with radio equipment to send a continuous distress message by pressing a single button.
  • Continue sending the distress signal even if the crew is incapacitated or otherwise engaged
  • Use a known MMSI like a “VHF phone number” to hail another DSC equipped vessel directly.  This avoids having to monitor high traffic channels or hailing your yachting friends on hailing and distress frequencies. It will alert your radio, similar to a telephone, that you have a call and then switch you automatically to the channel your caller has selected.
  • Have a “polling” feature that can transmit your vessel's position to a DSC-equipped monitoring station if properly connected to a GPS.
  • Will initiate a Search and Rescue (SAR) operation so if you set it off by mistake, here’s what you should do:
    • Answer anyone calling you back on the open channel and inform them that the signal was set off by mistake.  Then make a general radio announcement on Channel 16 to alert the Coast Guard so that a SAR mission is not undertaken (see next point).
    • Get on the VHF radio channel 16.  Either put out a general security call advising all traffic of a mistaken DSC alert signal or hail the Coast Guard directly.  Here are sample transmissions:
      • “Securite, securite, securite. Hello all stations. This is the sailing vessel (name) in vicinity of (where you are) at coordinates of (give lat/long GPS reading).  We are reporting a DSC signal set off by mistake.  Cancel alert.  Repeat, cancel DSC alert.  This is the sailing vessel (name) standing by on channel 16 for any concerned traffic.”
      • OR “US Coast Guard , US Coast Guard , US Coast Guard, this is the sailing vessel (name).”  Wait for a response. When the Coast Guard responds to you, say “US Coast Guard, this is the sailing vessel (name) reporting that a DSC signal was set off by mistake from our vessel.”  Then follow the Coast Guard’s instructions.  Chances are they will ask you to switch to channel 22a, the USCG working channel so they can get all your pertinent information.
    • Remember that if you don’t cancel the signal and an SAR is mounted, you could be held liable for the costs.
  • Allow an intercepting station to access all the information in your registration, including type of vessel, emergency contact information, cell phones onboard, and so on.
  • Function as a full featured VHF radio

DSC VHF radios DO NOT:

  • Take advantage of all these functions without registering for a unique MMSI number, inputting the code, and connecting with GPS.

For more information about the advantages of DSC, visit ICOM where they’ve posted a number of educational videos.


Joy of sailingCoastal Boating (Reg. in Ireland No. 443222) is a division of Knowledge Clinic Ltd.
Port Aleria, Rosnakilly, Kilmeena, Westport, Co. Mayo, Ireland - USA: PO Box 726, Mahwah, NJ 07430
All content on this site is subject to Copyright© - All rights reserved.
Contact us - Advertising - Privacy - Terms & Conditions - Copyright & Trademark - Webmaster