Raymarine RAY50, Installation And Operation Instructions Manual

Page: 58 / 116

7.1 Digital Selective Calling (DSC)
Traditional VHF radio systems require users to listen
until someone speaks, and then determine whether
the call is for them. DSC ensures that calls are
received by alerting or announcing the intended
recipient(s) first so they are ready to listen to the
subsequent message on the relevant channel.
DSC is part of the Global Maritime Distress
and Safety System (GMDSS), a maritime
communications system for emergency and distress
messages and all types of routine communications
such as ship-to-ship or ship-to-shore.
DSC is a digital signalling system, which operates
on VHF channel 70. DSC calls include other data
such as your vessel’s identification number, purpose
of the call, your position and the channel you want
to speak on.
DSC calls can be divided into 4 categories and are
prioritized as shown below:
1. Distress
2. Urgency
3. Safety
4. Routine
Distress
A Distress call should only be used when there is
imminent danger to a vehicle or person that requires
immediate assistance.
When making a distress call the following information
is transmitted to all stations within range:
• Vessel MMSI number.
• Vessel position (must be input manually if no GPS
position data is available).
• Local time (must be input manually if no GPS
position data is available).
• Nature of the distress (when designated).
• Transmission frequency.
The call is automatically repeated at approximately
4 minute intervals until it is acknowledged either by
a coast radio station (CRS) or a vessel within radio
range. Distress calls must be followed by a MAYDAY
call on priority channel 16.
Urgency
An urgency call should be used when there is
danger to a vehicle or person that does not require
immediate assistance.
When making an urgency call the following
information is transmitted to all stations within range:
• Vessel MMSI number.
• Vessel position (must be input manually if no GPS
position data is available).
• Local time (must be input manually if no GPS
position data is available).
• Transmission frequency.
Once an urgency call is sent it must be followed
with a PAN PAN voice message on channel 16 and
include the necessary details.
Safety
A safety call should be used when there is an
important navigational warning or meteorological
forecast/broadcast. Safety alerts can also used
for communications during search and rescue
operations.
When making a safety call the following information
is transmitted to all stations within range:
• Vessel MMSI number.
• Vessel position (must be input manually if no GPS
position data is available).
• Local time (must be input manually if no GPS
position data is available).
• Transmission frequency.
Once a safety call is sent it must be followed with
a SECURITE voice message on channel 16 and
include the necessary details.
Routine calls
Routine calls are used for contacting other vessels,
marinas, or shore stations.
Routine calls are made on channel 70 using the
dedicated Maritime Mobile Service Identity (MMSI)
number of the station to be contacted, selecting a
VHF working channel and sending the call. Both
radios automatically switch to the chosen channel
for conversation.
Routine calls can also be made to groups — When
groups of ships need the same information (yacht
races, club rallies etc.) a special group-call identity
can be used to enable restricted broadcast calls.
Note: To transmit precise positions, the radio
must be interfaced to a GPS receiver. Otherwise,
regular manual position updating is required.
58
Ray50 / Ray60 / Ray70