GMDSS VHF DSC procedures for small boat users
Updated 24 July 2024
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It’s best practice to:
- listen before transmitting
- be brief and concise
- always identify yourself
- speak clearly using prowords
- stick to ship’s business
- wait for a reply before re-transmitting
- try low power first except for distress
- keep a listening watch on Channel 16
Distress alert
Only to be used in the event of grave and imminent danger and assistance is required.
Send a distress alert using digital selective calling (DSC), (press and hold the button until the alert is sent).
On receipt of a DSC acknowledgement or after about 15 seconds, transmit the distress call and message on Channel 16:
Mayday, mayday, mayday
This is [name of own vessel – say 3 times].
Call sign or other identification
Maritime Mobile Service Identity (MMSI) of own vessel
Mayday
This is [name, call sign and MMSI].
Position [preferably as latitude and longitude].
Nature of distress
Assistance required
Number of persons on board
Other information
Over
Distress alert acknowledgement
When a DSC radio receives a distress alert it will sound an audible alarm.
Immediately cease any transmission that may interfere with distress traffic and continue a listening watch on Channel 16. If there is no DSC acknowledgement after a short interval (5 minutes) then, if you are able to offer assistance, acknowledge by voice on Channel 16:
Mayday
Name of vessel sending the distress message, followed by their call sign or MMSI
This is [name of own vessel – say 3 times]; Call sign or MMSI of your vessel
Received mayday
State what assistance you can give [including estimated time of arrival (ETA) if proceeding to the casualty]
Over
You should use any available means to relay the distress message to an appropriate coast station.
Urgency
If you are concerned about the safety of a person or vessel, you can send an urgency announcement using a DSC All Ships Urgency Call, nominating a working channel. Tune to Channel 16 to make the urgency call:
Pan pan, pan pan, pan pan
All stations – say 3 times.
This is [name of own vessel – say 3 times]
Call sign or other identification
MMSI of own vessel
Please go to Channel [nominated working channel]
Out
Tune to the working channel and send your urgency message.
Safety
To pass safety information to HM Coastguard (HMCG) use an Individual DSC call with safety priority if available on your radio, entering the appropriate MMSI number. Transmit the DSC call and wait for the Coastguard acknowledgement. Accept the acknowledgement and ensure your radio is on the working channel indicated in the response. You should wait for the Coastguard to contact you on that channel. If your radio does not support the call, then you should make a voice call on Channel 16.
Inter-ship – MMSI of other vessel known
Use an Individual DSC call with routine priority. Enter the MMSI or select from the directory and indicate the inter‑ship channel that will be used for radiotelephony (R/T) communication. When the called radio ‘rings’ the called vessel should acknowledge the DSC call. The conversation can then start on the selected inter‑ship channel.
Inter-ship – MMSI of other vessel unknown
Voice call on Channel 16, initially using low power, moving to an inter-ship channel once contact is established. If there’s no response, call on Channel 13, which is allocated in the GMDSS for bridge to bridge communications.
Coast station calls
Call the Coastguard (and other coast stations) that use DSC with an Individual DSC Call with routine priority, entering the MMSI of the required station or selecting from the radio’s directory.
When the Coastguard acknowledges the call, they will indicate the working channel for voice communications. Ensure your radio is set on the indicated working channel and wait for them to call you on it.
Global Maritime Distress and Safety System (GMDSS) sea areas
A map of the UK indicating the 3 sea areas around the coast and the coast of nearby European countries. White pointers indicate Medium Frequency (MF) and Very High Frequency (VHF) coast radio stations. Red pointers indicate a Very High Frequency (VHF) coast radio station.
Sea area A1
The radiotelephone coverage of VHF coast stations in which continuous alerting by DSC is available.
This area relates to a vessel with an antenna 4m above sea level. Where the antenna is lower or it is a portable radio, the area is smaller.
Sea area A2
The radiotelephone coverage of MF coast stations in which continuous alerting by DSC is available.
Sea area A3
The coverage of Inmarsat geostationary satellites.
Contacts
Ofcom
Ofcom
Riverside House
2a Southwark Bridge Road
London
SE1 9HA
Tel: +44 (0)207 981 3000
Maritime and Coastguard Agency
UK Technical Services Navigation
Spring Place
105 Commercial Road
Southampton
SO15 1EG
Tel: +44 (0) 203 817 2000
e-mail: infoline@mcga.gov.uk