Procedures for DSC communications on MF and VHF are described in sections “Distress” to “Testing the equipment used for distress and safety” below. The procedures for DSC communications on HF are in general the same as for MF and VHF.
- Distress
- Transmission of a DSC Distress Alert
- Appropriate action on receipt of a distress alert
- Distress Traffic
- Transmission of a Distress Relay Alert
- Acknowledgement of a DSC Distress Relay Alert received from a Coast Station
- Urgency
- Transmission of Urgency Messages
- Reception of an Urgency Message
- Safety
- Transmission of Safety Messages
- Reception of a Safety Message
- Public Correspondence
- DSC Channels for Public Correspondence
- Transmission of a DSC Call for Public Correspondence to a Coast Station or another Ship
- Repeating a Call
- Acknowledgement of a Call and Preparation for Reception of Traffic
- Reception of acknowledgement and further actions
- Testing the equipment used for distress and safety
- Special conditions and procedures for DSC communication on HF
- Distress
- Urgency
- Safety
- Public correspondence on HF
- Testing the equipment used for distress and safety on HF
Special conditions to be taken into account when transmitting DSC communications on HF are described in section “Special conditions and procedures for DSC communication on HF” below.
Distress
Transmission of a DSC Distress Alert
A distress alert should be transmitted if, in the opinion of the Master, a ship or a person is in distress and requires immediate assistance.
A DSC distress alert should, as far as possible, include the ship’s last known position and the time (in UTC) when it was valid. The position and the time may be included automatically by the Informed for Safe Navigation at Sea with Critical Maritime Informationship’s navigational equipment or may be inserted manually.
The DSC distress alert is transmitted as follows:
1 Tune the transmitter to the DSC distress channel (2 187,5 kHz on MF, channel 70 on VHF);
2 Time permitting, type in or select from the DSC equipment keyboard:
- the nature of distress;
- the ship’s last known position (latitude and longitude);
- the time (in UTC) the position was valid;
- the type of subsequent The Structure, Functions and Details of Professional Marine Radiocommunicationdistress communication (telephony), in accordance with the DSC equipment manufacturer’s instructions.
3 Transmit the DSC distress alert
5 Prepare for the subsequent distress traffic by tuning the Ship’s Antennas Systems and Radio Wave Propagationtransmitter and the radiotelephony receiver to the distress traffic channel in the same band, i. e. 2 182 kHz on MF, channel 16 on VHF, while waiting for the DSC distress acknowledgment.
NOTE: Some maritime MF radiotelephony transmitters shall be tuned to a frequency 1 700 Hz lower than 2 187,5 kHz, i. e. 2 185,8 kHz, in order to transmit the DSC alert on 2 187,5 kHz.
Appropriate action on receipt of a distress alert
Ships receiving a DSC distress alert from another ship should normally not acknowledge the alert by DSC since acknowledgment of a DSC distress alert by use of DSC is normally made by coast stations only.
Only in cases where no other station appears to have received the DSC distress alert, and the transmission of it continues, should the ship acknowledge it by use of DSC in order to terminate the call. Subsequently, the ship should inform a coast station or a coast earth station by any practicable means.
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Ships receiving a DSC distress alert from another ship should also defer the acknowledgment of the distress alert by radiotelephony for a short interval, if the ship is within an area covered by one or more coast stations, in order to give the coast station time to acknowledge the DSC distress alert first.
Ships receiving a DSC distress alert from another ship are required to:
- Watch for the reception of a distress acknowledgment on the Transmission of Urgency and Safety Signals from a Vesseldistress channel (2 187,5 kHz on MF and channel 70 on VHF);
- Prepare to receive the subsequent distress communication by tuning the radiotelephony receiver to the distress traffic frequency in the same band in which the DSC distress alert was received, i. e. 2 182 kHz on MF, channel 16 on VHF;
- Acknowledge receipt of the distress alert by transmitting the following by radiotelephony on the distress traffic frequency in the same band on which the DSC distress alert was received, i. e. 2 182 kHz on MF, channel 16 on VHF:
the 9-digit identity of the ship in distress, repeated 3 times
«this is»
the 9-digit identity or the call sign or other identification of own ship repeated 3 times
«RECEIVED MAYDAY»
NOTE: Ships out of range of a distress event or not able to assist should only acknowledge if no other station appears to acknowledge the receipt of the DSC distress alert.
Distress Traffic
On receipt of a DSC distress acknowledgment the ship in distress should commence the distress traffic by radiotelephony on the distress traffic frequency (2 182 kHz on MF, channel 16 on VHF) as follows:
- “’MAYDAY”;
- “this is”;
- the 9-digit identity and the call sign or other identification of the ship;
- the ship’s position in latitude and longitude or other reference to a known geographical location;
- the nature of distress and assistance wanted;
- any other information which might facilitate the rescue.
Transmission of a Distress Relay Alert
A ship knowing that another Distress Signals And Distress Trafficship is in distress shall transmit a DSC distress relay alert if:
- the ship in distress is not itself able to transmit the distress alert;
- the Master of the ship considers that further help is necessary.
The DSC distress relay alert is transmitted as follows:
1 Tune the transmitter to the DSC distress channel (2 187,5 kHz on MF, channel 70 on VHF),
2 Select the distress relay call format on the DSC equipment, type in or select on the DSC equipment keyboard:
- all Ships Call or the 9-digit identity of the appropriate coast station;
- the 9-digit identity of the ship in distress, if known;
- the nature of the distress situation
- the latest position of the ship in distress, if known;
- the time (in UTC) the position was valid (if known);
- type of subsequent distress communication (telephony);
- transmit the DSC distress relay call.
3 Prepare for the subsequent distress traffic by tuning the transmitter and the radiotelephony receiver to the distress traffic channel on the same band, i. e. 2 182 kHz on MF and channel 16 on VHF, while waiting for the DSC distress acknowledgment.
Acknowledgement of a DSC Distress Relay Alert received from a Coast Station
After having received and acknowledged a DSC distress alert, coast stations may, if necessary, retransmit the information received as a DSC distress relay call, addressed to all ships, all ships in a specific geographical area, a group of ships or a specific ship.
Ships receiving a distress relay call transmitted by a coast station should not use DSC to acknowledge the call, but should acknowledge the receipt of the call by radiotelephony on the distress traffic channel on the same band in which the relay call was received, i. e. 2 182 kHz on MF, channel 16 on VHF.
Acknowledge receipt of the distress alert by transmitting the following by radiotelephony on the distress traffic frequency on the same band on which the DSC distress relay alert was received:
- “MAYDAY”;
- the 9-digit identity or the call sign or other;
- identification of the calling coast station, “this is”;
- the 9-digit identity or call sign or other identification of own ship;
- “RECEIVED MAYDAY”.
Acknowledgement of a DSC Distress Relay Alert received from another Ship
Ships receiving a distress relay alert from another ship should follow the same procedure used in the acknowledgement of a distress alert, as discussed in section “Appropriate action on receipt of a distress alert” above.
Urgency
Transmission of Urgency Messages
The transmission of urgency messages shall be carried out in two steps:
- Announcement of the urgency message.
- Transmission of the urgency message.
The announcement is carried out by transmitting a DSC urgency call on the DSC distress calling channel (2 187,5 kHz on MF, channel 70 on VHF).
The Terrestrial Urgency and Safety Communications on the Vesselsurgency message itself is transmitted on the distress traffic channel (2 182 kHz on MF, channel 16 on VHF).
The DSC urgency call may be addressed to all stations or to a specific station. The frequency on which the urgency message will be transmitted should be included in the DSC urgency call. The transmission of an urgency message should thus be carried out as follows:
The Announcement:
1 Tune the transmitter to the DSC distress calling channel (2 187,5 kHz on MF, channel 70 on VHF).
2 Type in or select from the DSC equipment keyboard:
- all Ships Call or the 9-digit identity of the specific station;
- the category of the call (urgency);
- the frequency or channel on which the urgency message will be transmitted;
- the type of communication in which the urgency message will be given (e. g. radiotelephony), in accordance with the DSC equipment manufacturer’s instructions.
3 Transmit the DSC urgency call.
Transmission of the urgency message:
2 Tune the transmitter to the frequency or channel indicated in the DSC urgency call.
2 Transmit the urgency message as follows:
- “PAN PAN”, repeated 3 times;
- “ALL STATION” or called station, repeated 3 times;
- “this is”;
- the 9-digit identity and the call sign or other identification of own ship;
- the text of the urgency message.
Reception of an Urgency Message
Ships receiving a DSC urgency call announcing an urgency message addressed to all ships should NOT acknowledge the receipt of the DSC call, but should tune the radiotelephony receiver to the frequency indicated in the call and listen to the urgency message.
Safety
Transmission of Safety Messages
The transmission of safety messages should be carried out in two steps:
- Announcement of the safety message.
- Transmission of the safety message.
The announcement is carried out by transmitting a DSC safety call on the DSC distress calling channel (2 187,5 kHz on MF, channel 70 on VHF).
The safety message is normally transmitted on the distress and safety traffic channel on the same band on which the DSC call was transmitted, i. e. 2 182 kHz on MF, channel 16 on VHF.
The DSC safety call may be addressed to all ships, all ships in a specific geographical area, or to a specific station. The frequency on which the safety message will be transmitted should be included in the DSC call.
The transmission of a safety message is thus carried out as follows:
The Announcement:
1 Tune the transmitter to the DSC distress calling channel (2 187,5 kHz on MF, channel 70 on VHF).
2 Select the appropriate calling format for the DSC equipment (all ships, area call or individual call).
3 In accordance with the DSC equipment manufacturer’s instructions, type in or select from the DSC equipment keyboard:
- specific area or 9-digit identity of specific station, if appropriate;
- the category of the call (safety);
- the frequency or channel on which the safety message will be transmitted;
- the type of communication with which the safety message will be transmitted (e. g. radiotelephony);
4 Transmit the DSC safety call.
Transmission of the safety message:
1 Tune the transmitter to the frequency or channel indicated in the DSC safety call.
2 Transmit the safety message as follows:
- “SECURITE” repeated 3 times;
- “ALL STATIONS” or called station, repeated 3 times;
- “this is”;
- the 9-digit identity and the call sign or other identification of own ship;
- the text of the safety message.
Reception of a Safety Message
Ships receiving a DSC safety call announcing a safety message addressed to all ships should NOT acknowledge the receipt of the DSC safety call, but should tune the radiotelephony receiver to the frequency indicated in the call and listen to the safety message.
Public Correspondence
DSC Channels for Public Correspondence
VHF
The VHF DSC channel 70 is used for DSCs for distress and safety purposes as well as DSC for public correspondence.
MF
International and national DSC channels other than the DSC distress and safety calling channel, 2 187,5 kHz, are used for digital selective calling on MF for public correspondence.
Ships calling a coast station by DSC on MF for public correspondence should preferably use the coast station’s national DSC channel.
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The international DSC channel for public correspondence may, as a general rule, be used for communication between ships and coast stations of different nationalities. The ship’s transmitting frequency is 2 189,5 kHz, and the receiving frequency is 2 177 kHz.
The 2 177 kHz frequency is also used for digital selective calling between ships for general communication.
Transmission of a DSC Call for Public Correspondence to a Coast Station or another Ship
A DSC call for public correspondence to a coast station or another ship is transmitted as follows:
1 Tune the transmitter to the relevant DSC channel.
2 Select the format for calling a specific station on the DSC equipment.
3 Type in or select from the DSC equipment keyboard:
- the 9-digit identity of the station to be called;
- the category of the call (routine);
- the type of the subsequent communication (normally radiotelephony);
- a proposed working channel if c ailing another ship.
A proposed working channel should NOT be included in calls to a coast station; the coast station will, in its DSC acknowledgment, indicate a vacant working channel in accordance with the DSC equipment manufacturer’s instructions.
4 Transmit the DSC call.
Repeating a Call
A DSC call for public correspondence may be repeated on the same or another DSC channel, if no acknowledgement is received within 5 min.
Further call attempts should be delayed at least 15 minutes, if acknowledgement is still not received.
Acknowledgement of a Call and Preparation for Reception of Traffic
On receipt of a DSC call from a coast station or another ship, a DSC acknowledgement should be transmitted as follows:
- Tune the transmitter to the transmission frequency of the DSC channel on which the call was received.
- Select the acknowledgment format on the DSC equipment.
- Transmit an acknowledgement indicating whether the ship is able to communicate as proposed in the call (type of communication and working frequency).
- If able to communicate as indicated, tune the transmitter and the radiotelephony receiver to the indicated working channel and prepare to receive the traffic.
Reception of acknowledgement and further actions
When receiving an acknowledgement indicating that the called station is able to receive the traffic, prepare to transmit the traffic as follows:
- Tune the transmitter and receiver to the indicated working channel.
- Commence communication on the working channel by entering:
- the 9-digit identity, call sign, or other identification of the called station, “this is”;
- the 9-digit identity or call sign or other identification of own ship.
It will normally rest with the ship to call again a little later in cases where the acknowledgement from the coast station indicates that the coast station is not able to receive the traffic immediately.
In the cases where the ship, in response to a call to another ship, receives an acknowledgement indicating that the other ship is not able to receive the traffic immediately, it will normally rest with the called ship to transmit a call to the calling ship when ready to receive the traffic.
Testing the equipment used for distress and safety
Test transmissions using the exclusive DSC distress and safety calling frequency, 2 187,5 kHz, should be avoided as far as possible by using other methods.
Test transmissions should not be made on VHF DSC calling channel 70.
Test calls should be transmitted by the ship station and acknowledged by the called coast station. Normally there would be no thither communication between the two stations involved.
A test call to a coast station is transmitted as follows:
- Tune the transmitter to the DSC distress and safety calling frequency 2 187,5 kHz.
- Type in or select the format for the test call from the DSC equipment in accordance with the DSC equipment manufacturer’s instructions.
- Type in the 9-digit identity of the coast station to be called.
- Transmit the DSC call after checking as far as possible that no calls are in progress on the frequency.
- Wait for acknowledgment.
Special conditions and procedures for DSC communication on HF
The procedures for DSC communication on HF are – with certain additions described below – equivalent to the corresponding procedures for DSC communications on MF/HF.
Distress
Transmission of DSC distress alert
DSC distress alert should be sent to coast stations (e. g. in Sea Areas A3 and A4 on HF) and (on MF and/or VHF) to other ships in the vicinity.
The DSC distress alert should, as far as possible, include the ship’s last known position and the time (in UTC) when it was valid. If position and time are not inserted automatically from the ship’s navigational equipment, they should be inserted manually.
Ship-to-shore distress alert
Choice of HF hand
Propagation characteristics of HF radio waves for the actual season and time of the day should be taken into account when choosing HF bands for the transmission of DSC distress alerts.

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As a general rule the DSC distress channel on the 8 MHZ maritime band (8 414,5 kHz) may in many cases be an appropriate first choice.
The transmission of the DSC distress alert on more than one HF band will normally increase the probability of successful reception of the alert by coast stations.
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DSC distress alerts may be sent on a number of HF bands in two different ways:
a) Тeither by transmitting the DSC distress alert on one particular HF band, waiting a few minutes to receive acknowledgment by a coast station, and, if no acknowledgment is received within 3 minutes, repeating the process by transmitting the DSC distress alert on another appropriate HF band (and so on).
b) or by transmitting the DSC distress alert on a number of HF bands with no intervals between the calls, or only very short ones, without waiting for acknowledgment between the calls.
Procedure a) is recommended in all cases, where time permits it. This will make it easier to choose the appropriate HF band for commencement of the subsequent communication with the coast station on the corresponding distress traffic channel.
Transmitting the DSC alert
- Tune the transmitter to the chosen HF DSC distress channel (4 207,5, 6 312, 8 414,5, 12 577, 16 804,5 kHz).
- Follow the instructions for typing in or selecting relevant information from the DSC equipment keyboard as described earlier.
- Transmit the DSC distress alert.
NOTE: Ship-to-ship distress alerts should normally be made on MF and/or VHF, using the procedures for transmission of DSC distress alerts on MF/HF as described earlier. Some maritime HF transmitters shall be tuned to a frequency 1 700 Hz lower than the DSC frequencies given above, in order to transmit the DSC alert on the correct frequency. In special cases, for example in tropical zones, the transmission of DSC distress alerts on HF may, in addition to ship-to-shore alerting, also be useful for ship-to-ship alerting.
Preparation for the subsequent distress traffic
After having transmitted the DSC distress alert on appropriate DSC distress channels (HF, MF and/or VHF), prepare for the subsequent distress traffic by tuning the radiocommunication set(s) (HF, MF and/or VHF as appropriate) to the corresponding distress traffic channel(s).
If method b) described above has been used for transmission of the DSC distress alert on a number of HF bands:
- take into account on which HF band(s) acknowledgement has been successfully received from a coast station;
- if acknowledgements have been received on more than one HF band, commence the transmission of distress traffic on one of these bands, but if no response is received from a coast station then the other bands should be used in turn.
The distress traffic frequencies are:
HF (kHz): | Telephony | 4 125 | 6 215 | 8 291 | 12 290 | 16 420 |
Telex | 4 177,5 | 6 268 | 8 376,5 | 12 520 | 16 695 | |
MF (kHz): | Telephony | 2 182 | ||||
Telex | 2 174,5 | |||||
VHF: | Channel 16 (156,800 MHZ). |
Distress traffic
The procedures described earlier in section “Distress Traffic” are used when the distress traffic on MF/HF is carried out by radiotelephony. The following procedures shall be used in cases where the distress traffic on MF/HF is carried out by radiotelex:
1 The Forward Error Correcting (FEC) mode shall be used unless specifically requested to do otherwise.
2 All messages shall be preceded by:
- at least one carriage return;
- line feed;
- one letter shift;
- the distress signal “MAYDAY”.
3 The ship in distress should commence the distress telex traffic on the appropriate telex distress traffic channel as follows:
- carriage return, line feed, letter shift;
- the distress signal “MAYDAY”;
- “this is”;
- the 9-digit identity and call sign, or other identification of the ship;
- the ship’s position if not included in the DSC distress alert;
- the nature of the distress situation;
- any other information which might facilitate the rescue.
Appropriate action on reception of a DSC distress alert on HF from another ship
Ships receiving a DSC distress alert on HF from another ship should not acknowledge the alert, but should:
1 Watch for the reception of a DSC distress acknowledgment from a coast station.
2 While waiting for the reception of a DSC distress acknowledgement from a coast station, you should prepare for reception of the subsequent distress communication by tuning the HF radiocommunication set (transmitter and receiver) to the relevant distress traffic channel on the same HF band on which the DSC distress alert was received, while observing the following conditions:
- if radiotelephony mode was indicated in the DSC alert, the HF radiocommunication set should be tuned to the radiotelephony distress traffic channel on the HF band concerned.
- if telex mode was indicated in the DSC alert, the HF radiocommunication set should be tuned to the radiotelex distress traffic channel on the HF band in question. Ships able to do so should also watch the corresponding radiotelephony distress channel.
- if the DSC distress alert was received on more than one HF band, the radiocommunication set should be tuned to the relevant distress traffic channel on the HF band considered to be the best one for the case at hand. If the DSC distress alert was received successfully on the 8 MHZ band, this band may in many cases be an appropriate first choice
3 If no distress traffic is received on the HF channel within 1 to 2 minutes, tune the HF radiocommunication set to the relevant distress traffic channel on another HF band deemed appropriate to the case at hand.
4 If no DSC distress acknowledgement is received from a coast station within 3 minutes, and no distress communication is observed going on between a coast station and the ship in distress:
- transmit a DSC distress relay alert;
- inform a Rescue Coordination Centre by means of the appropriate radiocommunications.
Transmission of DSC distress relay alert
In cases where it is considered appropriate to transmit a DSC distress relay alert:
- Considering the current situation, decide on which frequency bands (MF, VHF, HF) the DSC distress relay alert(s) should be transmitted, taking into account ship-to-ship alerting (MF, VHF) and ship-to-shore alerting.
- Tune the transmitter(s) to the relevant DSC distress channel, following the procedures described above.
- Follow the instructions for typing in or selecting call format and relevant information from the DSC equipment keyboard as described earlier.
- Transmit the DSC distress relay alert.
Acknowledgement of an HF DSC distress relay alert received from a coast station
Ships receiving a DSC distress relay alert from a coast station on HF, addressed to all ships within a specified area, should NOT acknowledge receipt of the relay alert by DSC, but by radiotelephony on the telephony distress traffic channel on the same band(s) in which the DSC distress relay alert was received.
Urgency
The transmission of urgency messages on HF should normally be addressed:
- either to all ships within a specified geographical area;
- or to a specific coast station.
Announcement of the urgency message is carried out by the transmission of an urgency category DSC call on the appropriate DSC distress channel.
The transmission of the urgency message itself on HF is carried out by radiotelephony or radiotelex on the appropriate distress traffic channel on the same band on which the DSC announcement was transmitted.
Transmission of a DSC urgency message announcement on HF
- Choose the HF band considered to be the most appropriate, taking into account propagation characteristics for HF radio waves for the current season and time of day; the 8 MHz band may in many cases be an appropriate first choice.
- Tune the HF transmitter to the DSC distress channel on the selected HF band.
- Type in or select the appropriate call format from the DSC equipment for either geographical area call, or individual call.
- For area calls, type in specification of the relevant geographical area.
- Follow the instructions for typing in or selecting relevant information from the DSC equipment keyboard as described earlier, including type of communication by which the urgency message will be transmitted (radiotelephony or radiotelex).
- Transmit the DSC call;
- and, if the DSC call is addressed to a specific coast station, wait for DSC acknowledgement from the coast station. If acknowledgement is not received within a few minutes, repeat the DSC call on another appropriate HF frequency.
Transmission of the urgency message and subsequent action
1 Transmission of the urgency message and subsequent action.
2 If the urgency message is to be transmitted using radiotelephony, follow the procedure described in Section “Transmission of Urgency Messages”.
3 If the urgency message is to be transmitted by radiotelex, use the following procedure.
4 Use the Forward Error Correcting (FEC) mode unless the message is addressed to a single station whose radiotelex identity number is known.
5 Commence the telex message by:
- at least one carriage return, line feed, one letter shift;
- the urgency signal “PAN PAN”;
- “this is”;
- the 9-digit identity of the ship and the call sign or other identification of the ship;
- the text of the urgency message.
Announcement and transmission of urgency messages addressed to all HF equipped ships within a specified area may be repeated on a number of HF bands as warranted by the current situation.
Reception of an urgency message
Ships receiving a DSC urgency call announcing an urgency message should NOT acknowledge receipt of the DSC call, but should tune the intercommunication receiver to the frequency and communication mode indicated in the DSC call in order to receive the message.
Safety
The procedures for transmission of DSC safety announcements and safety messages are the same as for urgency messages described above, except that:
- the DSC announcement shall include the category SAFETY;
- the safety message shall include the safety signal “SECURITE” instead of the urgency signal “PAN PAN”.
Public correspondence on HF
The procedures for DSC public correspondence communication on HF are the same as those for MF. Propagation characteristics should be taken into account when transmitting DSC communications on HF. The national and international HF DSC channels used for DSC distress and safety purposes differ from those used for DSC public correspondence.
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Ships calling an HF coast station by DSC for public correspondence should preferably use the coast station’s national DSC calling channel.
Testing the equipment used for distress and safety on HF
Procedures for testing the ship’s equipment used for DSC distress, urgency and safety calls on HF by transmitting DSC test calls on HF DSC distress channels, are the same as those used for testing on the MF DSC distress frequency, 2 187,5 Hz.