Marine VHF
Marine Radio
Choose the right priority, understand what Channel 16 and Channel 70 actually do, and deliver the essential facts without blocking distress traffic.
If a DSC distress alert is available and correctly set up, send it on Channel 70, then make the voice MAYDAY on Channel 16. The digital alert identifies the vessel and may include position; the voice message explains what is happening and what help is needed.
DSC unavailable or not ready, or no time to operate it? Go directly to a voice MAYDAY on Channel 16. Do not delay the call while navigating menus.
Four levels that must not be blurred together
MAYDAY, PAN-PAN, SÉCURITÉ, and a routine call do different jobs. Use the highest priority justified by the real situation—never a higher one merely to obtain a faster reply.
Use when
A vessel or person is in grave and imminent danger and immediate assistance is required: sinking, fire out of control, collision with serious danger, person overboard not recovered, or a life-threatening medical emergency.
Not for
A breakdown in safe water, a request for a tow with no developing danger, or an inconvenience that can be handled routinely.
Typical channel path
DSC distress alert on 70 if available → voice MAYDAY and distress traffic on 16.
Use when
A very urgent message concerning the safety of a vessel or person, but without grave and imminent danger right now: loss of propulsion drifting toward risk, a serious but currently stable medical problem, or concern for an overdue vessel.
Not for
Routine assistance, marina arrangements, traffic updates, or a situation that already meets the MAYDAY threshold.
Typical channel path
Supported DSC urgency announcement on 70 → brief PAN-PAN announcement on 16 → full message on the nominated working channel.
Use when
Important navigational or meteorological information: an unlit obstruction, a newly observed hazard, dangerous debris, or a local warning that other vessels need promptly.
Not for
A personal route report, casual weather discussion, routine calling, or a request for help with your own vessel.
Typical channel path
Individual DSC safety call to a coast station → its assigned working channel; or, for an appropriate all-ships warning, a brief announcement on 16 → working channel.
Use when
Calling another vessel, marina, harbour, coast station, pilot, or service when there is no distress, urgency, or safety broadcast.
Not for
Any situation needing immediate or priority attention for the safety of life or a vessel.
Typical channel path
Individual DSC routine call on 70, a published local calling channel, or a very brief call on 16 → voice conversation on a permitted working channel.
Channel 16, Channel 70, and working channels
The simplest useful model is: Channel 70 rings the digital alarm, Channel 16 carries priority voice calling, and a working channel carries the conversation.
Use Channel 16 for voice distress, urgency, very brief safety communication, and initial calling when another permitted method is unavailable. Keep listening when required and practical, and immediately protect any distress traffic.
Do not hold routine conversations, make radio checks, or give long non-distress explanations on 16.
Channel 70 is reserved for Digital Selective Calling. A DSC packet can carry MMSI, priority, a requested voice channel and, for distress, position when the radio has current GNSS data.
No voice is transmitted on 70—not conversation, a radio check, or even the spoken word MAYDAY.
Move routine calls and longer urgency or safety messages to a permitted ship-to-ship, port, VTS, or coast-station channel selected for that service and location.
There is no universal working channel for every place and purpose. Use the current local channel plan or the channel assigned by the station.
National channel plans and equipment capabilities differ. For example, Channel 9 may be a recreational calling channel in some U.S. areas, while UK ship-to-ship working channels include 6, 8, 72, and 77. Treat these as local assignments, not worldwide defaults.
MAYDAY: the complete distress workflow
The red distress button does not replace the voice call. DSC attracts attention and supplies machine-readable data; Channel 16 supplies the human situation report.
- 1
Confirm readiness before the emergency
The radio needs the vessel’s valid MMSI and a current position from an internal or connected GNSS receiver. Check this before every trip, not during the casualty.
- 2
Send the distress alert on Channel 70
Lift the cover and hold the DISTRESS control as the radio instructs. Select the nature of distress only when time permits; do not delay an alert to complete optional fields.
- 3
Follow with voice on Channel 16
Return or switch to 16 and transmit the MAYDAY call and message. Follow the radio display and local authority procedure; UK MCA guidance says to speak after DSC acknowledgement or about 15 seconds.
If DSC is unavailable or time is critical
Select Channel 16 and start the voice MAYDAY immediately, using high power when necessary. Give the position early. A clear partial message now is more useful than a perfect message sent too late.
- MAYDAY · MAYDAY · MAYDAY
- THIS IS · [vessel name ×3] · [call sign] · [MMSI]
- MAYDAY · THIS IS [vessel name, call sign, MMSI]
- MY POSITION IS [latitude/longitude, or bearing and distance from a known point]
- [nature of distress and immediate danger]
- I REQUIRE [specific assistance]
- [number of people aboard; injuries or people in the water]
- [vessel description, survival equipment, intentions, other useful facts]
- OVER
Stay on Channel 16 and keep the radio available. Repeat the call if no reply is received after a reasonable interval, update the rescue authority if the situation or position changes, and follow its instructions.
PAN-PAN and SÉCURITÉ: announce first, then move the detail
These calls have priority over routine traffic but do not create MAYDAY distress traffic. Keep the Channel 16 announcement short and name the working channel for the full message whenever the applicable procedure allows it.
If supported, send an All Ships DSC urgency announcement on 70 and nominate a working channel. Make the short PAN-PAN announcement on 16, switch to the nominated channel, then give position, problem, assistance or advice required, people affected, and intentions.
Short announcement
PAN-PAN · PAN-PAN · PAN-PAN ALL STATIONS · ALL STATIONS · ALL STATIONS THIS IS [vessel name ×3, call sign, MMSI] PLEASE GO TO CHANNEL [working channel] OUT
On the working channel, repeat PAN-PAN and identification, then give the full urgent message. If the danger becomes grave and imminent, upgrade immediately to MAYDAY.
Not every recreational DSC radio can transmit an urgency category. USCG notes that boater VHF sets may receive urgency/safety DSC calls without being able to send them. Verify the controls on your radio and use the local voice procedure when the category is unavailable.
When reporting a hazard, use an Individual DSC safety call or the published coast-station/VTS method and follow the acknowledgement to its working channel; that path does not require a separate all-ships announcement. If local procedure calls for a broad warning, make only a brief safety announcement on 16 and transmit the actual warning on the nominated working channel.
Short announcement
SÉCURITÉ · SÉCURITÉ · SÉCURITÉ ALL STATIONS · ALL STATIONS · ALL STATIONS THIS IS [vessel or station identification] SAFETY MESSAGE ON CHANNEL [working channel] OUT
The safety message should identify the hazard, its precise position, time observed, movement if any, and the area or vessels affected.
Coast stations often announce official weather and navigation information on 16, then transmit it on a published working channel. Monitor the local plan instead of assuming one worldwide broadcast channel.
Routine communication: call briefly, talk elsewhere
Routine does not mean unimportant; it means no distress, urgency, or all-ships safety priority. The discipline is to identify clearly and free the calling channel quickly.
Send an Individual DSC call with ROUTINE priority on Channel 70 and nominate a permitted voice channel. After the called set acknowledges, both radios switch or are directed to that channel for the conversation.
Use the published local calling channel. If Channel 16 calling is permitted and no priority traffic is active, call briefly on low power, establish contact, agree a working channel, and move at once.
Use the channel published for that service. Port-operation and vessel-movement channels are restricted to operational and safety traffic; they are not general chat channels.
MARY JANE · MARY JANE THIS IS BLUE DUCK · BLUE DUCK CHANNEL ONE SIX · OVER BLUE DUCK · THIS IS MARY JANE REPLY CHANNEL SIX EIGHT · OVER SIX EIGHT · OUT
- Listen before transmitting and never interrupt distress traffic.
- Try low power for routine nearby calls; use the power needed for distress.
- Identify the station called and your own vessel on every initial call.
- Think through the message first; speak slowly, clearly, and briefly.
- Move off 16 as soon as contact is established.
- Wait for a reply before repeating; do not fill the channel with rapid calls.
Make the radio useful before leaving the berth
DSC is only as good as its identity, position source, operator knowledge, and local channel information.
- 1Program the correct MMSI and keep the vessel name and call sign beside the set.
- 2Confirm that the displayed position and UTC time are current and update automatically.
- 3Carry the station licence and qualified operator required by your flag state and cruising area.
- 4Keep the local channel plan, coastguard, port, marina, and VTS channels accessible.
- 5Test on a designated radio-check or working channel—never test MAYDAY on 16 or DSC distress on 70.
This is a learning summary, not a substitute for the radio’s manual, an operator certificate course, or instructions from the local coastguard, VTS, or licensing authority. Channel assignments and mandatory watchkeeping differ by country, vessel, and waterway.
Official references
UK MCA — GMDSS VHF DSC procedures for small boatsUK MCA — safe use of VHF Channels 16 and 70USCG — radio information and MAYDAY procedure for boatersUSCG — DSC urgency and safety calls