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Spotlight on Digital Selective Calling (DSC)

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Boaters have a safety tool aboard which is often overlooked and can enhance their comfort zone on a bad day at sea. It lives under that little red door on the VHF called “Distress”.

Since 2000, all fixed mount VHF radios sold have been required to have DSC emergency functions.  Early DSC VHFs had single receivers which scanned between listening on channel 70 and the set station. This meant a signal could be missed even if for a short period.  The newer units, Class D, have two receivers with one dedicated for the DSC function – so one receiver is always tuned to CH 70.

If you have this feature built into your VHF, the first thing is you need to do is to make it specific to your boat. This means you need an MMSI, Mobile Maritime Service Identity number issued by the national authority in the country where your vessel is registered. In the US this is the FCC.  A quirk in the US system is that if you get your MMSI from BoatUS or similar agencies it is not registered in the International Database. Only those numbers issued by the FCC are in the International data base.

You can go online at http://www.itu.int/cgi-bin/htsh/mars/ship_search.sh and see if your MMSI number is there. If not, you need to take steps to correct this if you operate outside US waters. An MMSI that is not registered in the International database will delay an emergency response when the number is received at a SAR center. In other words if you need help it will be delayed – not the best situation if you are sinking, etc.

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Once you have the MMSI get your VHF manual which has instructions on how to program the DSC function. It will ask for the number and your boat name. Another often overlooked instruction is that the VHF needs a position input. Normally, the NMEA output of a GPS incorporating your position into its messages, without a position distress message, is useless.

Spotlight on Digital Selective Calling (DSC) – PART 2

Your VHF is now ready to transmit an emergency message to all vessels within VHF range. This message, at a minimum, will give your MMSI number, the vessel’s name and its location – this is a distress message. It will then switch automatically to channel 16 to monitor any replies to your call – from there it is handled like any other distress situation.  Your VHF has now set an alarm off in EVERY DSC-equipped VHF within range, typically a 15-25 mile circle of your vessel. This alarm signal is annoying, loud, and overrides the volume setting on receivers and it is sure to get attention—whereas a May-Day broadcast on 16 may not.  The listening station may not be on 16, may have the squelch set too high, the volume turned down or no one is listening – the DSC feature cuts thru these issues and gets attention.

Newer VHFs have additional DSC features for the Distress Message – a menu of messages can also be sent, along with the distress signal, to alert the responder as to the type of distress – making it an even more valuable tool as the responder can evaluate its nature and take action even if there is no additional voice communication. Perhaps the sender is too busy to work a voice connection or the nature of the distress has progressed beyond their ability to function. Whatever the reason, the message has been sent & received and the name of the vessel, location and nature of the distress are stored in the memory of the receiver’s VHF; however, as with any distress it is better to establish voice communication guaranteeing the responders can be coordinated.

Spotlight on Digital Selective Calling (DSC) – PART 3

Ships are no longer required to maintain a listening watch on Channel 16 – many do, but in the future DSC will be the only way to contact them, and a call to all ships or to their specific MMSI number is required. New systems are becoming a must for cruising safety and general communication.

How to Do The VHF Radio Distress Call

Dave Cooper spent over 20 years designing & marketing computers, in the U.S. and Japan.  He sailed to the Caribbean in the mid 70s where he ran seasonal private charters throughout the islands for a decade, then worked in the yachting industry in the BVI until 2006. He retired on his classic trawler Swan Song and cruises the southern Caribbean.

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