Marine Communication


Digital Selective Calling (DSC)

For current use of DSC and monitoring or radio transmissions check with government agencies. [Government index]

The latest marine radio technology is called Digital Selective Calling (DSC) and will be incorporated into all marine radios. VHF-DSC is an internationally recognized standard that operates on channel 70 of the VHF maritime mobile band. Aside from functioning as a VHF radiotelephone, a VHF-DSC (digital selective calling) radio permits the selective reception of digital calls from other VHF-DSC radios on ships and at Coast Guard centres. The important safety feature of the VHF-DSC radio is that it allows a ship in distress to transmit a rapid distress alert at the push of a button. When connected to a GPS receiver, the distress alert will send an accurate position of the distressed vessel.

DSC is now used on VHF, MF and HF maritime radios as part of the GMDSS (global marine distress and safety) system. Channel 70 (VHF) and 2187.5 KHz (MF) are reserved exclusively for DSC safety and distress calls. There are DSC calling channels in each HF band.

Channel 70 will be monitored for the new distress signals when the U.S. and Canadian Coast Guard communications systems are upgraded. Some USCG stations have installed equipment for direction-finding (on your radio signal) and digital voice recording. USCG cutters are equipped, but smaller rescue boats are not. Many towboat operators will also be equipped.

By international rules, commercial ships are required to be DSC equipped and to monitor Channel 70. The International Maritime Organization (IMO) will allow commercial ships to stop monitoring Channel 16, but Coast Guard radio stations will continue monitoring Channel 16.

The radio's "mayday button" initiates an automated distress call which is heard by all nearby vessels and the Coast Guard. The digital (not voice) transmission will contain an encoded distress call including vessel information such as your location (the radio should be connected to a GPS) and the radio user's personal information (if provided to the Coast Guard). It receives and stores messages, provides "caller-ID", automatically issues a "Mayday" and stores a reply if you are disabled.

By 2002, more than half of VHF radios sold wereDSC equipped. However, for older radios to work properly in an emergency, DSC radio users need to register the radio's identity (boat and contact information) with the Coast Guard so this information is added to the search and rescue database. An identificaton number, Maritime Mobile Service Identity (MMSI), is encrypted in your radio. This useful feature of DSC allows you to "call another MMSI" much like you would on a cell phone! The radio will automatically switch both radios to a working voice channel once a call is answered.

Global Maritime Distress and Safety System GMDSS

On Feb. 1, 1999, Global Maritime Distress and Safety System GMDSS went into effect for all large ships by an international treaty signed in 1988. DSC and EPIRB (satellite-based emergency position indicator beacon), Immarstat, the coastal NAVTEX system, and high seas SafetyNET are all part of the new system. Canadian coastal stations will not be fully equipped for GMDSS for several years.

A copy of "The Future in Marine Radio Communications - GMDSS" (a PDF document by the U.S. Coast Guard) is provided here in Web format for convenience. It explains the new international marine emergency system.

From the U.S. Coast Guard web site:
"When fully implemented, DSC will eliminate the need for persons on a ship's bridge or on shore to continuously guard radio receivers on voice radio channels, including VHF channel 16 (156.8 MHz) and 2182 kHz now used for distress, safety and calling. A listening watch aboard GMDSS-equipped ships on 2182 kHz ended on 1 February 1999, and on VHF channel 16 is scheduled to end on 1 February 2005."

Read what the Canadian Coast Guard said about the future of VHF Channel 16 - they plan to monitor Channel 16 and 2182 kHz in Canada until pleasure boats have access to DSC-equipped radios. ( Government Index)

Ships will be required to monitor Channel 16 until 2005, but boaters should expect some to ignore this. If you cannot hail the bridge of a large vessel (over 20 metres/66 feet), try calling them on Channel 13, which they will still be required to guard.

Check with government agencies for current use of DSC and monitoring or radio transmissions.

Note that "pleasure yachts not engaged in trade" are exempted from the international requirement for ships at sea to have GMDSS equipment.