To take advantage of the GMDSS/MMSI system your vessel must be equipped with a radio that has DSC.
DSC VHF radios WILL
Have a One-Button Emergency Transmit capability that sends out the vessel's unique MMSI number and, if properly connected to a GPS or Loran, the vessel's latitude/longitude position.
Continue sending the distress signal even if the captain is incapacitated.
Allow for a non-experienced VHF user to send, with the pressing of one button, a goof-proof continuous distress message.
Privately hail another DSC equipped vessel, or shore station, with a known MMSI number. Like having a "VHF phone number" this avoids having to monitor high traffic channels just for a hail from your boating buddy. It even "rings" your radio, similar to a telephone, notifying you that you have a call and then switches you automatically to the channel your caller is waiting on.
If properly connected to a Loran or GPS, a "Polling" feature transmits your vessel's position, in digital display, that can be monitored by DSC equipped home station/fleet station or boat.
Fully function as all other regular VHF radios.
DSC VHF radios WILL NOT
Be monitored by the U.S. Coast Guard in all areas until that area's Rescue 21 system is operational (see map). However, DSC equipped vessels in the area may receive your distress call.
Provide private radio to radio voice communication. After the "private" digital hail, DSC radios automatically switch to an open VHF channel for voice communications. Voice communication is carried on an active working channel chosen by the caller making the initial hail.
Take advantage of all these functions without first registering for a unique MMSI number that is free for the boaters who register on this site.
DSC capable VHF radios are available at West Marine