On the 1st January 1999, Vhf Channel 16 was deemed by the International Maritime Orginisation, too no longer require to have a person listening to it on a headset 24 hours a day.
HM Coastguard decided (because we are nice people) that we would carry on until 2005 to give everyone chance to buy a new radio.
DSC stops the requirement for vessels at sea to monitor channel 16 for distress traffic, as they will have all distress calls alerted by a very loud and annoying alarm, and all routine calls by a not so loud and annoying alarm.
Dsc therefore ensures that your calls routine or distress will not be missed, and all distress calls will be passed including a position (If you have it coinnected to a GPS) and a unique id, just by pressing a big red button for 5 seconds. If able you should then follow up with a normal Mayday/Pan call but if the boat is burning around your feet you can leave it at just the Dsc call.
It should be noted that commercial vessels (That had to be ready for dsc in 1999) may not be listening on channel 16 anymore as channel 13 is the primary bridge to bridge channel.
Sorry about the longwinded explanation, if you have any more questions I will be pleased to answer them, or ring your local coastguard centre, they will be only to happy to help.
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