Why the rules exist

Marine VHF is a shared, life-saving resource. Every operator must follow strict rules on licensing and channel use so that distress calls always get through and interference is kept to a minimum.

Licensing - two separate things

You need TWO licences to legally operate marine VHF/DSC in the UK:

• The ship's Radio Licence (issued by Ofcom) - covers the equipment fitted to a specific vessel, gives the vessel its Call Sign and MMSI number.
• The operator's certificate - the SRC (Short Range Certificate) itself, which qualifies a named person to use the set. This is issued once you pass the RYA/Ofcom exam and never expires, though the physical card can be reprinted.
• At least one person on board holding a valid SRC must be present whenever the radio is used on a vessel required to carry one.

MMSI and Call Sign

• The MMSI (Maritime Mobile Service Identity) is a unique 9-digit number programmed into the set, used for DSC (Digital Selective Calling) - it identifies the vessel automatically in distress and routine digital calls.
• UK-flagged small craft MMSIs typically start with 235 or 232.
• The Call Sign is a separate identifier (letters/numbers) used for voice calling.

Key working channels

• Channel 16 (156.8 MHz) is the international distress, safety and calling channel - monitor it whenever the set is on, but do not chat on it.
• Channel 70 is reserved exclusively for DSC digital alerting - never use it for voice.
• Channel M (37) and Channel M2 (80) are common UK marina/yacht club working channels.
• Channel 6, 8, 72, 77 are ship-to-ship working channels for routine chat, moving off 16 as soon as contact is made.
• Channel 0 is used by UK HM Coastguard for SAR (Search and Rescue) coordination.
• Channel 13 is the bridge-to-bridge navigation safety channel.

Power and dual-watch

• Marine VHF sets typically transmit at 25 watts (high power) or 1 watt (low power) - use low power for short-range working to reduce congestion.
• 'Dual watch' lets you monitor Channel 16 and a working channel simultaneously.

Common mistakes

• Forgetting that Channel 70 is data-only, not for voice - a classic exam trap.
• Believing the SRC expires - it does not, but a lost card must be replaced via RYA.
• Confusing the ship's licence (the boat) with the operator's certificate (the person) - you need both.
• Leaving a conversation running on Channel 16 instead of shifting to a working channel immediately.

Why routine calls matter

Most VHF traffic is routine working - not distress, urgency or safety. Getting the procedure right keeps Channel 16 clear and shows the examiner you understand correct radio discipline.

The two-stage principle

Channel 16 is for calling and distress only, never for a full conversation. Every routine contact follows the same shape:

• Call up on Ch16 (or a pre-arranged working channel if already agreed)
• Agree a working channel
• Switch together and pass the actual message there

Making the initial call

Format: name of the station called (up to 3 times, max), 'THIS IS', your vessel name and callsign (up to 3 times), OVER.

Example: 'Solent Coastguard, Solent Coastguard, THIS IS Sea Breeze, Sea Breeze, callsign Mike Golf X-ray Two Three, OVER.'

Use the name/callsign only twice if contact is already established or conditions are good - three times is for poor conditions or first contact.

Answering a call

The called station replies with its own name once, 'THIS IS', the caller's name, then invites a channel: 'Sea Breeze, THIS IS Solent Coastguard, received, switch to channel 67, OVER.' The calling vessel confirms and both move together.

Working channel etiquette

• Channel 16 is not used to chat - move off it within about one minute of contact
• UK small craft working channels include 6, 8, 72, 77 and M/M2 (marina/yacht club use)
• Channel 70 is reserved for DSC digital calling only - never voice
• Always check the channel is clear before transmitting

Ending a call

Use 'OUT' when the exchange is finished - never say 'OVER AND OUT', which is a common exam trap since the two contradict each other. Use 'OVER' only when you expect a reply.

Correct phonetic alphabet and numbers

All callsigns, names and identifiers are spelled using the NATO phonetic alphabet (Alfa, Bravo, Charlie...). Numbers are spoken digit by digit (e.g. 156.8 is 'one five six decimal eight'), except round figures like 100 which may be 'one hundred'.

Common mistakes to avoid

• Holding a full conversation on Channel 16
• Forgetting to say OVER, leaving the other station unsure who should speak
• Saying OVER AND OUT together
• Skipping the callsign or vessel name
• Not confirming the working channel clearly before switching

Watchkeeping

All vessels fitted with VHF DSC should maintain a listening watch on Channel 70 (DSC) and Channel 16, except when actually transmitting on a working channel.

What MAYDAY is for

MAYDAY is the international radiotelephony distress call. Use it only when a vessel or person is threatened by grave and imminent danger and requires immediate assistance - fire, flooding, sinking, person overboard with no other help, or someone seriously injured. Never use it for anything less urgent - that is what PAN PAN (urgency) and SECURITE (safety) are for.

The voice MAYDAY format

Speak clearly and slowly on Channel 16 (or a DSC-designated distress channel once contact is made). The standard order is:

• MAYDAY MAYDAY MAYDAY
• THIS IS (vessel name, said three times)
• MAYDAY (vessel name once more)
• Position (latitude/longitude or bearing and distance from a known point)
• Nature of distress (sinking, fire, collision, etc.)
• Assistance required
• Number of persons on board
• Any other important information (sea state, injuries, abandoning ship)
• Say OVER at the end and wait for a reply.

DSC distress alerts

Digital Selective Calling (DSC) sends an automatic distress alert at the push of the red guarded button on a DSC-fitted VHF set (Channel 70). Hold the button for at least 5 seconds. This transmits your MMSI, position (from GPS input), time, and nature of distress if pre-selected, without you needing to speak. After sending the DSC alert, you must follow up with a full voice MAYDAY on Channel 16 as soon as possible, because the DSC alert alone does not tell rescuers the full story.

Cancelling a false alert

If you accidentally trigger a DSC distress alert, you must immediately cancel it. Send an all-ships voice message on Channel 16: MAYDAY, ALL STATIONS, ALL STATIONS, ALL STATIONS, THIS IS (vessel name and MMSI), CANCEL MY DISTRESS ALERT OF (time UTC). Failing to cancel wastes Coastguard resources and can trigger a real search.

Receiving a MAYDAY

If you hear a MAYDAY and you're not best placed to help, stay silent and keep listening (maintain radio silence) unless called directly or asked to relay, so as not to clutter the channel. If no shore station acknowledges within a short time and you can help, you may relay the message as MAYDAY RELAY.

Common mistakes

• Forgetting to say OVER, leaving the channel blocked.
• Not holding the DSC button the full 5 seconds.
• Skipping the follow-up voice MAYDAY after a DSC alert.
• Confusing MAYDAY with PAN PAN or SECURITE.
• Giving a vague position instead of exact coordinates.

Urgency and safety calls: PAN PAN and SECURITE

VHF has three call classes above routine traffic: DISTRESS (MAYDAY), URGENCY (PAN PAN) and SAFETY (SECURITE). Knowing which one to use, and on which channel, is a core SRC exam theme.

PAN PAN - the urgency signal

• PAN PAN means a very urgent message concerning the safety of a vessel, aircraft or person, but there is NOT yet grave and imminent danger requiring immediate assistance.
• Say the word PAN PAN THREE times to open the call, spoken 'pahn pahn' - it comes from the French 'panne' meaning breakdown.
• Typical uses: engine failure and drifting toward danger, a person injured but not life-threatening, a vessel disabled but not sinking, or being medically unwell and needing advice.
• Sent on Channel 16 (or a DSC alert followed by voice on 16), then usually asked to move to a working channel.
• Structure mirrors a MAYDAY: PAN PAN x3, called station or ALL STATIONS x3, THIS IS, vessel name x3 and callsign, position, nature of urgency, assistance required, number of persons on board, other useful info, OVER.
• A PAN PAN can be escalated to MAYDAY if the situation worsens - always reassess.

SECURITE - the safety signal

• SECURITE (say 'securitay' x3) announces an important navigational or meteorological warning - it is NOT about an emergency to a specific vessel.
• Typical uses: gale warnings, navigational hazards such as a drifting container or unlit buoy, ice reports, or a broadcast of a nearby distress relay.
• Method: the SECURITE call itself is given on Channel 16, then the actual detailed message is broadcast on a working channel (announced during the call), keeping Channel 16 clear.
• Usually broadcast by Coastguard or a port authority, but any vessel spotting a hazard should report it.

The key exam distinction

• MAYDAY = grave and imminent danger, immediate help needed.
• PAN PAN = urgent, but not immediately life-threatening.
• SECURITE = information/warning broadcast, not a request for help at all.

Common mistakes

• Saying PAN PAN only once or twice instead of three times.
• Confusing SECURITE (a warning broadcast) with PAN PAN (an urgent situation call).
• Forgetting that all three call types are always initiated on Channel 16 (or via DSC) before moving to a working channel.
• Using MAYDAY for situations that are only urgent, which can cause an over-response and ties up Channel 16.
• Forgetting to switch back to Channel 16 after the working-channel traffic finishes.

What is DSC?

Digital Selective Calling (DSC) is an automated distress and calling system built into modern VHF sets. It lets you send a distress alert at the touch of a button, without needing to speak. Every DSC-fitted VHF radio must have an MMSI programmed in before it can transmit.

MMSI basics

• MMSI stands for Maritime Mobile Service Identity.
• It is a unique 9-digit number that identifies your vessel, like a phone number for your boat.
• UK leisure MMSIs are issued free by Ofcom, alongside your Ship Radio Licence.
• The MMSI is programmed into the set once, usually by the dealer or installer, because most sets only allow a small number of changes before locking - always get this right first time.
• The first three digits are the Maritime Identification Digits (MID) - 232, 233, 234 and 235 identify the UK.

DSC distress calling

• Press and hold the red distress button (usually under a spring-loaded cover) for about 5 seconds to send a DSC distress alert on Channel 70.
• The alert automatically transmits your MMSI and, if the set is linked to a GPS, your position and time.
• After sending the distress alert, you must follow up with a voice Mayday on Channel 16, giving vessel name, position, nature of distress and persons on board.
• Channel 70 is reserved for DSC only - never use it for voice traffic.

Other DSC call types

• Routine, safety and urgency calls can also be made by DSC, each specifying the channel to switch to for the follow-up voice conversation.
• Individual calls use the other vessel's MMSI to alert just them.
• All ships calls alert every DSC set in range.

Equipment and fitting

• A DSC VHF set must be connected to a GPS source (internal or external) so distress alerts carry accurate position data.
• Sets should be tested regularly using the DSC test call function to a Coastguard station, never a live distress test.
• An MMSI is boat-specific, not owner-specific - if you sell the boat, the MMSI normally stays with the licence and should be re-registered.
• Handheld VHFs with DSC also need their own MMSI, separate from the fixed set.

Common mistakes

• Forgetting that Channel 70 is for DSC data only, not conversation.
• Entering the MMSI wrong and not being able to correct it - always double-check before confirming.
• Assuming a plain (non-DSC) handheld can send a distress alert - it cannot, it is voice-only.
• Not linking the set to GPS, meaning distress alerts go out with no position.

What GMDSS actually is

GMDSS stands for the Global Maritime Distress and Safety System. It is not one gadget - it is a joined-up set of equipment and procedures (VHF DSC, EPIRB, SART, AIS, MF/HF where fitted) designed so a vessel in trouble can alert rescuers fast, even if nobody is physically on watch listening to the radio.

EPIRBs - the big red beacon

An EPIRB (Emergency Position Indicating Radio Beacon) transmits on 406 MHz to satellites, giving your position and a unique identity code to rescue authorities worldwide.

• Modern EPIRBs include built-in GPS, so position accuracy is typically within about 100 metres, and the alert reaches the rescue chain within minutes.
• Every EPIRB must be registered with the Maritime and Coastguard Agency (MCA) in the UK - an unregistered beacon slows rescue because responders cannot identify the vessel or owner.
• EPIRBs can be float-free (auto-release from a bracket if the vessel sinks) or manual release. Float-free types must be serviced and battery-checked to manufacturer intervals, usually every 5 years for the battery.
• Common mistake: candidates confuse EPIRB (satellite, global, distress only) with a VHF DSC distress alert (line-of-sight, regional, but faster to raise other vessels nearby). Use both together in a real emergency - DSC alerts nearby traffic instantly, EPIRB brings in full SAR coordination.

SART - Search and Rescue Transponder

A SART does not send a distress message itself. It sits passive until triggered by a nearby radar (usually a searching ship or aircraft radar in the 9 GHz X-band), then it returns a distinctive line of dots on that radar's screen, guiding the rescuer straight to the survival craft.

• Range is limited to radar horizon - typically a few miles from a ship, more from an aircraft.
• AIS-SART is the modern equivalent, showing up as a series of AIS position reports on plotters and ECDIS rather than a radar dot pattern.
• Common mistake: thinking SART calls for help - it doesn't. It is a homing aid used AFTER a distress alert has already been raised by DSC or EPIRB.

AIS - Automatic Identification System

AIS broadcasts a vessel's identity, position, course and speed automatically over VHF frequencies, letting other AIS-fitted vessels and shore stations see who is nearby and avoid collision.

• Class A is mandatory for SOLAS vessels (broadly, commercial ships over 300 gross tons on international voyages); Class B is the common fit for leisure and small commercial craft, transmitting less often and with lower power.
• AIS is a collision-avoidance and situational-awareness tool, not primarily a distress system, though AIS-SART and man-overbord AIS beacons piggyback on the same technology for search and rescue.
• Common mistake: relying on AIS alone for collision avoidance - not every vessel carries it, so it supplements, never replaces, a proper visual and radar lookout.

Exam tip

Learn which device does what job: DSC alerts, EPIRB brings the cavalry, SART/AIS-SART gets you found once help is close, AIS is everyday traffic awareness.