Sign In/Up with USCGAUX
Sign Up/In with USCGAUX
Help Video - Job Aide
SEARCH NATIONAL SITE
SECURITY LEVELS

Beep Beep! DSC Calls and Alarms

 

If you see that a boat has a DSC-capable VHF radio aboard (easily identified by the red “DISTRESS” button) and it is properly configured, you may want to mention this little-appreciated capability of DSC, sometimes called “DSC alarm.”

DSC stands for Digital Selective Calling: it’s a way to ring a particular VHF radio in the same way one would ring a particular cell phone. It is not well-known that DSC radios have the ability to sound these “rings” (alarms) even when their volume is turned down. This is an ingenious feature, as it means that e.g. boaters anchored overnight with people sleeping aboard can be alerted to emergencies by leaving their radio on and the volume turned all the way down. It also means that those in distress can summon help quickly by pressing a button, even if they are unable to speak.

DSC alarms are more reliable than voice communication, and in some cases they can travel farther. A properly configured DSC radio transmits the location of the vessel in distress to all nearby craft. If your boat has the DSC radio connected to the chartplotter, a marker will automatically be placed on the chart at the location of the distress call.

This is critically important because the most likely source of rescue is usually a boat near you. The recommended procedure for calling MAYDAY is to always send a DSC distress call by pressing the red "DISTRESS" button. This sounds a DSC alarm on nearby radios before you start speaking. This means that you should:

  • always have the DSC feature properly configured so the red “distress” button will work
  • press the red “distress” button first if you need to call “mayday” (hold it down as prompted by the radio)
  • keep your VHF radio on at all times with the volume turned down, even when you are not keeping a radio watch 

This article has focused on DSC alarms and mayday calls, but DSC can also be used for many other purposes. A DSC "ring" can call a friend's boat and ask them to switch to a particular working channel automatically, DSC can perform a semi-automatic radio check, a DSC call will obtain the location of another boat without speaking it on the radio, or DSC call be used to "ring" a group of boats but exclude other boats. Some man-overboard devices can be programmed to "ring" your own boat when activated using a DSC call. See your DSC radio's operating manual for details.  

Three minutes of this attached video can be shown to demonstrate a DSC alarm. The VHF radio on this sailboat is sounding a DSC distress alarm in rough weather. The crew uses this alarm to rescue the survivors from a sinking vessel nearby well before any search and rescue craft would be able to respond. This is because the DSC alarm has alerted nearby boats.

Activity: play indicated segment of this video (about 3 mins after the start point given):

Discuss how DSC alerting worked in this video.

Updated 2023-Jul-10 by Christian Sandvig, SO-CM