Canadian Yachting October 2023 - 40

USING DIGITAL
SELECTIVE CALLING
(DSC) - by Peter Bennett, Radio Training Officer,
Vancouver Power and Sail Squadron
What Is DSC?
The Digital Selective Calling system provides a system for
digital signalling between vessels, and between vessels
and shore stations, using VHF channel 70.
The signals transmitted include distress, urgency and
safety alerts, and requests to initiate routine calls. The
Class D VHF-DSC radios currently available include two
receivers. One receiver is permanently tuned to Channel
70 to receive DSC alerts, and the other can be tuned as
desired for normal voice communication use. Any voice
communication that is a result of a DSC alert will occur
on a normal inter-ship or ship/shore voice channel.
MMSI And MI Numbers
Digital Selective Calling uses Maritime Mobile Service
Identity (MMSI) numbers to identify vessels and shore
stations. An MMSI number is a unique nine-digit number
assigned to a vessel.
If a vessel has more than one marine radio, the same
number will be used by all radios, and also by an AIS
(Automatic Identification System) transponder if fitted.
The MMSI number belongs to the vessel and remains
with the vessel if it is sold. The DSC functions of the
radio will not work unless an MMSI has been entered
into the radio.
Most radios will only permit you to enter an MMSI once.
If it is necessary to change the MMSI in a radio, you will
have to contact the manufacturer or service depot to
have the current MMSI erased before a new one can
be entered.
The MMSI for a vessel starts with a three-digit country
code (316 for Canada), followed by six digits identifying
the individual vessel. Coast Guard shore station MMSIs
start with two zeros, then the country code and individual
number.
Hand-held radios with DSC and GPS not associated with
a vessel can get a Maritime Identity (MI) number, essentially
an MMSI starting with 8, then the country code
and individual identifier.
MMSIs and MIs are issued free of charge by the federal
department, Innovation, Science and Economic Development,
Spectrum Management Branch (ISED-SM) through
a website which you can find by doing a web search for
MMSI Application Canada. That search should take you
to Application Form A/B for an individual station MMSI.
To get the form for a hand-held MI, search for MI Application
Canada. You should receive your MMSI or MI by
email within a few business days after submitting the
application form.
If you purchase a boat with a DSC-equipped radio, you
must change the contact information for the MMSI using
the application forms listed above.
Distress Calls
A primary use of Digital Selective Calling is to transmit a
distress alert containing the vessel's MMSI, position and
the nature of distress.
Most radios are available with a built-in GPS receiver to
provide the position. If the radio does not have a GPS
receiver, it should be connected to the data output of a
chart plotter or external GPS receiver to obtain position
data. If there is no GPS data available, the latitude and
longitude should be entered manually every four hours
and before transmitting the distress alert.
Before transmitting a distress alert, you may select the
nature of distress from a menu of eleven items: Undesignated,
Fire/Explosion, Flooding, Collision, Grounding,
Capsizing, Sinking, Adrift, Abandoning Ship, Piracy or
Man Overboard. If you do not set the nature of distress,
the distress alert will show the nature of distress as
Undesignated.
The DSC distress alert must be followed by a normal
voice distress call. The voice distress call should include
the vessel's MMSI so that listeners can link the DSC distress
alert with the voice call, and know that there is
only one distress situation.
Stations receiving a DSC distress alert will sound the
Radiotelephone Alarm Signal (two alternating tones)
and will display the sending station's MMSI, position
and nature of distress, and may, depending on settings,
immediately change to Channel 16 to receive the voice
distress call. Most radios can be set to change to Channel
16 immediately, or to pause, allowing the user to cancel
the channel switch.
Routine Calls
To make a routine DSC call to another station, go to
the DSC menu and select Individual Call, then enter the
other station's MMSI and the desired working channel.
Press Call to send the call. The addressed station's radio
will sound an alarm and display Routine Call from your
MMSI and proposed working channel. When the other
40 CANADIAN YACHTING | OCTOBER 2023
Canadian Yachting October 2023

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