Group DSC Primer for Fleets and Safety: Group Calls on your VHF

A new use for Digital Selective Calling

Not just for safety anymore, DSC can be used to contact another boat for purely recreational reasons, such as to set up a lunch. Not only that, you can set your radio to be part of a “group” to send and receive alerts intended for a fleet of vessels. This capability may serve any fleet, be it yacht club, regatta, or just a group of friends.

VHF Radio

The DSC Basics

Every DSC-capable VHF should be connected to a GPS and be programmed with the vessel’s MMSI number.  The MMSI (“Maritime Mobile Service Identity”) is a unique number, like a phone number, and can be obtained from your national registrar (FCC in the US) or, for US use only, from BoatUS or others. The FCC license has a fee and may be used for individual and group calls, and may be used internationally.  The BoatUS MMSI is free, cannot be used for international travel, can be used to make group calls, and cannot be used to generate a new group MMSI. Only one MMSI number should be used on all equipment used on a boat (VHF, SSB, VHF handhelds, AIS, AIS emergency beacons).  The FCC in the United States does not allow a user to change an AIS MMSI:  if a change is desired, it must be done by an authorized dealer.   If you ever decide to travel out of the US, it would be wise to obtain an FCC MMSI for the boat, rather than send the AIS unit back to the dealer.  An FCC issued MMSI is also listed in the international database provided to international rescue groups, while a BoatUS MMSI is not.   Since an MMSI stays with a boat when it is sold, it is wise to have an FCC MMSI, so that the boat can be sailed in foreign waters, after the sale, without changing the MMSI entered into electronics at the dealer or manufacturer.

The MMSI identifies your vessel when making or receiving a DSC call, whether it’s an emergency transmission or just a normal contact.  VHF radios have directories that allow users to store commonly-called MMSI’s for ease of use.  Some older radios do not have a separate group directory; newer ones do.

Procedures vary for placing DSC calls, depending on the VHF model, but all include selecting the MMSI of the recipient, specifying the nature of the call and sometimes the working channel, and initiating the transmission.  The recipient will hear an alert tone on their radio and depending on radio model and nature of call, the radio may switch to the appropriate channel to complete the traffic.  Some radios require accepting and acknowledging a DSC call before switching to the channel proposed by the caller, by pushing a button on the microphone.  Please see your radio’s instructions.

About Groups

It’s now possible to create groups and to contact all group members at once.  As it turns out, this is pretty simple. If you add a “Group MMSI” into your group directory, then calls transmitted to that group will cause your radio to respond and change to the working channel.  For a regatta or a fleet cruising in company this may be a huge convenience. 

No separate license, fee or special programming is required.

Group MMSI

Every DSC radio has a directory to enter the MMSI numbers for boats that are called frequently, and newer radios have a separate directory for group MMSI numbers.  One does not need to change your MMSI or a get a separate license to use group MMSI calling.  Group calls allow radio calling to all members of a group that have the group MMSI call entered into the group directory.  

There is no formal program for issuing Group MMSIs. A Coast Guard site explains how you may generate your own legal one.  Simply put, you take an existing MMSI, knock the zero off the end and add a zero to the front, so 123456780 would become 012345678. 

When you add this number to your VHF radio group directory, the radio will become part of that group.  Calls placed to the group will now be received by all members within range (usually about 25 nm) including YOUR radio.

CCA Members Only: We have created such a number. You may find it here if logged in. This should be placed as an entry in your group directory, since you want to be part of this group for both send and receive.

Benefits of groups

Boat-to-boat VHF DSC group calling creates significant day-to-day benefits.    

1. VHF radios now have an “extra set of ears” on watch, listening for calls from the group(s) you’re affiliated with. You can leave the radio on VHF 16 as required and still not miss those fleet calls.

2. Yachts traveling together can provide quick mutual support, coordinate a cruise, or get advice about weather, anchorages, sailing conditions, technical problem etc.   This semi-private multi-party conference call is a perfect solution for a cruise.   This allows allow quick, nearby support, advice or assistance from other cruisers, before it becomes an emergency.  The advantage of this on a cruise would be a group call would ring on every boat on the cruise within VHF range and switch everyone's radio, when acknowledged, to a group working frequency. 

 Some additional DSC items for Emergencies and Urgency

There are some USCG numbers you may wish to have in your radio for emergencies.  Program these into your INDIVIDUAL, and not group, directory unless you want to be listening in on group Coast Guard calls.

Ship Group. The U.S. Coast Guard group ship station call identity is 036699999.  Calls to all U.S Coast Guard ships within VHF range can be made by entering 036699999 in the INDIVIDUAL directory and then placing a DSC call.  

Shore Group. The U.S. Coast Guard DSC group coast station identity is 003669999 (note the two zeroes.  A call goes to USCG only).  Calls to all Coast Guard coast stations within VHF range can be made by entering 003669999 in the INDIVIDUAL directory and then placing a DSC call.  This will allow discussions of a routine, Securite or Pan-Pan nature to take place with the Coast Guard easily before a situation becomes a Mayday.  

Some radios do not allow entry of a group number in the individual directory.  I could not enter the CG ships MMSI in the individual directory in the ICOM 92d, but I was able to enter both CG ships and the Coast Guard into the individual calling directory of a Vertex Standard GX2100.  Interestingly, I was able to enter the group CG MMSI into the individual directory of the ICOM 92d.  

One can call a group from the group directory.  The Coast Guard should be entered and called from the individual directory, since one does not want to receive all Coast Guard group traffic[1] .  It is helpful to enter the ship's MMSI into the individual directory of all of the ship's radios and handhelds.   With this, one can call to or from the vessel and the dinghy (especially when the outboard stops and before you float out to sea!)

Your local district. A complete list of USCG MMSI group numbers for local sectors and groups can be found at http://www.uscg.mil/acquisition/rescue21/dsc.asp  Having your local number programmed in may be helpful in reaching them in an urgent situation.

By Charles Starke, MD

revised 1/7/2017