RYA SRC/VHF cheat sheet

GMDSS sea areas: A1 within VHF DSC coast range (~20-30 nm); A2 beyond A1 but within MF DSC range (~100 nm); A3 beyond A2 within Inmarsat coverage (roughly 70°N-70°S); A4 polar regions outside A2/A3, relying on HF.

Distress, urgency and safety have priority in that order over all other traffic; a distress call suspends normal working until the distress is resolved or the net is formally closed.

GMDSS functional requirements: alerting, SAR coordination, locating, on-scene communications, maritime safety information (MSI), and general/public correspondence.

VHF band is 156-174 MHz, FM, line-of-sight; range is set mainly by antenna height, not by transmitter power.

A VHF DSC-equipped vessel in Sea Area A1 must carry a VHF DSC radio with channel 70 watch, plus a 406 MHz EPIRB (or 121.5 MHz SART alternative per carriage rules) and a NAVTEX receiver or other MSI receiver.

Channel 70 is DSC only; voice on channel 70 is prohibited, and channel 16 is the distress/safety/calling voice channel.

The phonetic alphabet and figure code (e.g. 'niner', 'decimal') are used to avoid confusion; 'MAYDAY' = distress, 'PAN PAN' = urgency, 'SECURITE' = safety.

Radio horizon in nautical miles is approximately 1.23 × √(antenna height in feet), or 2.2 × √(height in metres) for each antenna.

Channel 16: distress, safety and calling; initial contact is made here then moved to a working channel.

Channel 70: DSC only. Channel 06: inter-ship. Channel 13: bridge-to-bridge navigation safety (low power). Channel 09: marina/port working in many areas.

Channel 10: often used for lock and bridge communications; channel 12: port operations in many regions; channel 67: small craft safety (UK).

Dual watch monitors channel 16 plus one selected channel; tri-watch monitors 16, the selected channel and channel 70 (DSC).

Squelch suppresses background noise between transmissions; set it just above the point where noise stops. Volume controls audio loudness only.

High/low power: use low power (typically 1 W) for short-range working; switch to high power (25 W) only when needed.

Channel spacing is 25 kHz; a set must be able to transmit on all channels it is certified for, but channel 70 must not transmit voice.

ATIS (Automatic Transmitter Identification System) is required on inland waterways in some countries; it transmits the vessel identity after each voice transmission and must be disabled at sea.

Voice MAYDAY format: MAYDAY ×3, this is [vessel name] ×3, MAYDAY [name and call sign], position, nature of distress, assistance required, persons on board, any other information, OVER.

MAYDAY RELAY is used when another station relays a distress on behalf of a vessel unable to transmit.

PAN PAN ×3 is for urgent messages concerning safety of a vessel or person but not immediate grave danger; SECURITE ×3 precedes safety broadcasts (e.g. navigation warnings, weather).

DSC distress alert: lift the protective cover, press and hold the DISTRESS key for about 5 seconds until the alert transmits; the alert contains MMSI and, if connected, position and time.

After a DSC distress alert, transmit the MAYDAY voice call on channel 16 (or the channel indicated by the coast station) and await acknowledgement.

A distress alert should be cancelled/annulled by DSC or voice if transmitted in error; a MAYDAY RELAY or 'SILENCE MAYDAY' is used by the controlling station to impose radio silence.

Distress acknowledgement by a coast station is normally by DSC, followed by voice on channel 16; ship stations should not acknowledge DSC distress alerts unless in a position to assist and no coast station has responded.

On receipt of a distress alert, keep watch on channel 16 and the DSC channel, and only transmit if you can assist or acknowledge as a relay.

MMSI is a 9-digit number: ship station MMSI starts with MID (3 digits) identifying the flag state; group MMSI starts with 0; coast station MMSI starts with 00.

DSC distress alert is sent on channel 70 (VHF) or 2187.5 kHz (MF) or HF distress frequencies; routine DSC calls are made on channel 70 then voice on a working channel.

DSC call categories: DISTRESS, URGENCY, SAFETY, ROUTINE; the category determines the priority and handling.

A DSC routine call includes the called station's MMSI, your MMSI, and the proposed working channel; the called station replies by DSC then both switch to the working channel for voice.

Position and time in a DSC alert are taken from the GPS input; without GPS the position must be entered manually and updated.

DSC controller should be programmed with the vessel's MMSI; the MMSI must match the EPIRB and any other DSC equipment.

A DSC 'distress alert acknowledgement' from a coast station is normally followed by a voice MAYDAY ACK on channel 16.

Do not test DSC on channel 70 except with a coast station or another vessel using a routine call and a working channel for the test voice traffic.

The vessel requires a Ship Radio Licence (or equivalent) issued by the flag state; operators require a certificate of competence (e.g. SRC for VHF, LRC for HF).

The SRC certificate is the minimum operator qualification for VHF DSC and is recognised under the ITU Radio Regulations.

Radio silence: 'SILENCE MAYDAY' or 'SILENCE DISTRESS' imposes silence; 'SILENCE FINI' lifts it.

Identification: use the vessel name and call sign; the call sign is assigned with the licence.

Keep a radio log where required; record distress, urgency and safety traffic, and any malfunction.

Do not transmit on channel 16 except for distress, safety, calling and brief replies; move to a working channel for the conversation.

Do not use profanity, do not transmit without identification, and do not interfere with distress traffic; such acts are offences under national law.

Radio equipment must be type-approved for the service; modifications or use of non-approved equipment can invalidate the licence.

406 MHz EPIRB: transmits to the Cospas-Sarsat satellite system, contains the vessel MMSI/identity and, with GPS, position; 121.5 MHz is used for local homing.

EPIRB registration is mandatory and must be updated when the vessel changes owner, flag, or MMSI; registration links the beacon to the vessel and emergency contacts.

EPIRB battery life: typically 48 hours at -20 °C; check the expiry date and the test indicator monthly using the self-test (not the live transmission).

EPIRB should be mounted in a float-free bracket, clear of obstruction, and be manually operable; stow it where it can be reached in an abandon-ship situation.

SART (Search and Rescue Transponder) operates on 9 GHz (X-band) radar; when interrogated by a radar it shows a line of 12 dots on the radar display.

SART range is typically about 5-10 nm depending on radar height; it should be mounted at least 1 m above sea level and switched on only in an emergency.

Battery care: keep batteries charged, avoid deep discharge, and replace according to manufacturer intervals; test the radio on low power to avoid interfering with distress traffic.

Antenna care: keep the antenna vertical, free of corrosion, and undamaged; a poor VSWR reduces range; do not transmit without an antenna connected.

If a distress alert is received by DSC, acknowledge only if you are in a position to assist and no coast station has acknowledged; otherwise maintain watch.

MAYDAY RELAY format: MAYDAY RELAY ×3, this is [relay station] ×3, MAYDAY [original vessel], followed by the original distress details.

If your own vessel is in distress and time permits, send a DSC distress alert first, then the voice MAYDAY on channel 16.

If the radio fails, use any other means: satellite phone, mobile phone, flares, EPIRB, SART, or visual signals.

Abandon ship: take the EPIRB and SART with you, activate the EPIRB, and switch on the SART when clear of the vessel.

On receipt of a MAYDAY, write down the details (position, nature, persons on board) and inform the coast station if not already aware.

Radio silence: the station controlling the distress (usually a coast station) may impose silence; all other stations must comply.

Do not transmit a distress alert as a test; use the self-test or a routine DSC call for testing.

VHF DSC watch on channel 70 must be maintained continuously when the radio is on; some sets offer dual watch with channel 16.

NAVTEX receives MSI on 518 kHz (international), 490 kHz (national) and 4209.5 kHz; it prints or displays messages automatically.

406 MHz EPIRB alerts are routed to a Rescue Coordination Centre (RCC) via the Cospas-Sarsat system; the RCC then coordinates SAR.

SART and AIS-SART are locating devices; AIS-SART transmits on AIS frequencies and shows on AIS displays.

Battery capacity: VHF handhelds typically 5 W; check charge before departure and carry spare batteries.

Distress frequencies: VHF channel 16 (voice) and channel 70 (DSC); MF 2182 kHz (voice) and 2187.5 kHz (DSC); HF 4125, 6215, 8291, 12290, 16420 kHz (voice).

Radio checks should be made with a coast station or another vessel on a working channel, not on channel 16, using low power.

Listen before transmitting on a channel to avoid interrupting existing traffic, especially on channel 16.

Use standard phraseology: OVER (invitation to reply), OUT (end of communication), ROGER (received), WILCO (will comply), STANDBY.

Keep transmissions brief; identify with the vessel name and call sign at the start and end of the communication.

Do not use channel 16 for routine calls; make initial contact, then move to a working channel.

Respect privacy: do not divulge personal information over the air; remember that anyone can listen.

Use the correct channel for the purpose: 16 for distress/safety/calling, 06 for inter-ship, 13 for bridge-to-bridge, 70 for DSC only.

If you hear a distress call, do not transmit unless you can assist or are acknowledging; keep the channel clear.

Switch off ATIS when leaving inland waterways and entering sea areas, and switch on when entering inland waterways where required.

MMSI is issued with the ship radio licence; it is programmed into the DSC controller and EPIRB and must not be changed without re-licensing.

The MID (Maritime Identification Digits) identifies the flag state; e.g. 232/233/234/235 for UK, 244/245/246 for Netherlands.

A group MMSI (starting with 0) is used for calling a group of vessels, e.g. a fleet or race committee.

A coast station MMSI starts with 00; a SAR aircraft MMSI starts with 111.

The EPIRB registration database (e.g. in the UK, the MCA) must hold current vessel details and emergency contacts; failure to register can delay rescue.

Licence renewal: check the expiry date; operating without a valid licence is an offence.

Operator certificate: the SRC certificate is personal and not transferable; keep it on board or available for inspection.

Changes of vessel name, owner, or MMSI must be notified to the licensing authority and the EPIRB registry.

Charge handheld batteries fully before departure; lithium-ion batteries lose capacity with age and heat; store in a cool dry place.

Do not leave a handheld radio transmitting on high power for long periods; it drains the battery and can overheat.

Check the antenna connection and coax for corrosion; a damaged antenna reduces range and can damage the transmitter.

Keep the antenna vertical and as high as possible; height dominates range more than power.

Use the correct charger voltage; a wrong charger can damage the battery or radio.

Test the radio and DSC self-test before departure; record the test in the radio log if required.

Spare batteries and a spare antenna are recommended for offshore passages; a handheld is a useful backup to the fixed VHF.

Do not transmit with the antenna disconnected; this can damage the transmitter output stage.

MAYDAY: spoken three times, then 'THIS IS' and vessel name three times, then MAYDAY and name/call sign once, position, nature of distress, assistance required, persons on board, other information, OVER.

PAN PAN: spoken three times, then 'THIS IS' and vessel name three times, then PAN PAN and name/call sign, position, nature of urgency, assistance required, OVER.

SECURITE: spoken three times, then 'THIS IS' and vessel name, then SECURITE and name/call sign, followed by the safety message.

Distress acknowledgement by a coast station: MAYDAY [vessel], THIS IS [coast station], RECEIVED MAYDAY, followed by instructions.

If you hear a distress call and no one responds, you may acknowledge as a relay: MAYDAY [vessel], THIS IS [your vessel], RECEIVED MAYDAY.

Impose silence: 'SILENCE MAYDAY' or 'SILENCE DISTRESS' by the controlling station; 'SILENCE FINI' to lift it.

Cancel a false alert: transmit MAYDAY [vessel], THIS IS [vessel], CANCEL MY DISTRESS ALERT, followed by the reason.

Use 'MAYDAY RELAY' when relaying a distress on behalf of a vessel unable to transmit.

Sea Area A1: within VHF DSC coverage of a coast station (typically 20-30 nm); requires VHF DSC, EPIRB, and MSI receiver.

Sea Area A2: beyond A1 but within MF DSC coverage (~100 nm); requires MF/HF DSC or Inmarsat, in addition to A1 equipment.

Sea Area A3: beyond A2 within Inmarsat coverage (approx. 70°N-70°S); requires Inmarsat or HF DSC.

Sea Area A4: polar regions outside A2/A3; requires HF DSC and other equipment.

Carriage requirements depend on the sea area the vessel operates in; a vessel must be equipped for the highest sea area it enters.

The GMDSS allows distress alerting to be initiated automatically from the vessel, and SAR coordination to be carried out by shore authorities.

MSI is received via NAVTEX (within ~200 nm of a coast station) or Inmarsat Enhanced Group Call (EGC) for wider areas.

Locating devices (SART, AIS-SART) and survival craft VHF radios are part of the GMDSS equipment for larger vessels.

Radio check: call a coast station or another vessel on a working channel, not channel 16; use low power.

Format: '[station called] THIS IS [your vessel and call sign], RADIO CHECK, OVER.' Reply: 'RADIO CHECK, RECEIVED YOU LOUD AND CLEAR' or 'WEAK BUT READABLE'.

Routine DSC call: select the called station's MMSI, category ROUTINE, propose a working channel; send; wait for DSC acknowledgement; switch to the working channel for voice.

Do not use channel 70 for voice; it is reserved for DSC.

Use the correct working channel for the area; local port operations channels vary by country.

Keep a listening watch on channel 16 when the radio is on, unless the set is on DSC watch only.

Identify at the start and end of each transmission; use 'OVER' and 'OUT' correctly.

Do not transmit on channel 16 for routine traffic; move to a working channel after initial contact.

EPIRB activation: manual (switch) or automatic (float-free) when the vessel sinks; once activated it transmits on 406 MHz and 121.5 MHz.

406 MHz signal is detected by Cospas-Sarsat satellites; the 121.5 MHz signal is used by aircraft and rescue vessels for homing.

EPIRB self-test: use the test function (usually a short press) to check battery and transmission; do not activate the live distress transmission for a test.

SART: switch on when abandoning ship; it responds to X-band radar (9 GHz) with a line of 12 dots; range depends on radar height.

SART should be mounted at least 1 m above sea level; it has a battery life of typically 96 hours in standby and 8 hours in operation.

AIS-SART transmits position and identity on AIS; it appears on AIS displays and does not require radar.

EPIRB battery expiry date must be checked; replace before expiry; the battery typically lasts 5 years.

Register the EPIRB with the national authority; the registration links the beacon to the vessel and emergency contacts.

Ship Radio Licence: issued by the flag state; authorises the use of the radio equipment on board; must be kept on board.

Operator certificate: SRC (Short Range Certificate) for VHF; LRC (Long Range Certificate) for HF; GOC/ROC for commercial vessels.

The licence specifies the equipment, the MMSI, and the call sign; changes must be notified.

Radio silence: 'SILENCE MAYDAY' or 'SILENCE DISTRESS' imposes silence; 'SILENCE FINI' lifts it.

Distress traffic has absolute priority; all other transmissions must cease.

Do not transmit false or deceptive distress signals; this is a criminal offence.

Keep a radio log where required; record distress, urgency, safety traffic and equipment malfunctions.

Use of non-type-approved equipment can invalidate the licence and is an offence in many countries.

DSC distress alert: press and hold DISTRESS for ~5 seconds; the alert is transmitted on channel 70 with the vessel MMSI, position and time.

The alert is received by coast stations and other vessels within range; the RCC coordinates the SAR response.

After the DSC alert, transmit the MAYDAY voice call on channel 16; the coast station acknowledges by DSC and voice.

If no acknowledgement is received, repeat the DSC alert or use other means (Inmarsat, HF, EPIRB).

A distress alert can be relayed by another station (MAYDAY RELAY) if the vessel cannot transmit.

The RCC may request vessels in the area to assist; vessels should respond if able.

False alerts must be cancelled immediately by DSC and voice to avoid unnecessary SAR response.

Distress alerting is free of charge and has priority over all other traffic.

Channel 16: 156.800 MHz, distress/safety/calling.

Channel 70: 156.525 MHz, DSC only.

Channel 06: 156.300 MHz, inter-ship.

Channel 13: 156.650 MHz, bridge-to-bridge navigation safety, low power.

Channel 09: 156.450 MHz, marina/port working in many areas.

Channel 67: 156.375 MHz, small craft safety (UK).

Channel 10: 156.500 MHz, lock and bridge communications in many areas.

Channel 12: 156.600 MHz, port operations in many regions.

Listen before transmitting; do not interrupt existing traffic, especially on channel 16.

Use standard phraseology: OVER, OUT, ROGER, WILCO, STANDBY, SAY AGAIN.

Keep transmissions brief and to the point; identify with vessel name and call sign.

Do not use channel 16 for routine calls; move to a working channel.

Respect privacy; do not divulge personal information over the air.

Do not transmit profanity or offensive language; it is an offence.

Do not transmit without identification; always identify at the start and end.

Switch off ATIS when leaving inland waterways and entering sea areas, and switch on when entering inland waterways where required.

GMDSS requires a reserve source of energy (battery) to power the radio equipment for a specified period (e.g. 1 hour for VHF, 6 hours for MF/HF) if the main power fails.

The reserve battery must be charged and tested regularly; check the voltage and capacity.

Handheld VHF radios with spare batteries are a useful backup; keep them charged.

Satellite phones and mobile phones are not part of GMDSS but can be used as a backup in an emergency.

Flares, EPIRB and SART are visual/radio locating devices for abandon-ship situations.

Test the reserve battery and the emergency lighting regularly.

Know how to switch to the reserve battery and emergency antenna if the main equipment fails.

Keep a copy of the distress procedures and important phone numbers on board.

The MMSI is a 9-digit number; it must be programmed into the DSC controller and must match the EPIRB and licence.

Do not change the MMSI without re-licensing; an incorrect MMSI can delay rescue.

The DSC controller should have the vessel's position and time from GPS; without GPS, enter position manually and update it.

The DSC controller should be programmed with the vessel's call sign and name for identification.

Group MMSI (starting with 0) is used for calling a group of vessels.

Coast station MMSI starts with 00; SAR aircraft MMSI starts with 111.

The DSC controller should be tested regularly using the self-test function.

Keep a record of the MMSI and the licence on board.

VHF DSC radio with channel 70 watch is required for Sea Area A1.

MF/HF DSC or Inmarsat is required for Sea Areas A2 and A3.

HF DSC is required for Sea Area A4.

NAVTEX receiver or Inmarsat EGC is required for MSI reception.

406 MHz EPIRB is required for all sea areas.

SART or AIS-SART is required for larger vessels; check the carriage requirements for your vessel.

Battery and antenna maintenance: check regularly, replace as needed, and test the equipment before departure.

Keep the radio log and equipment manuals on board.

VHF channel 16: 156.800 MHz, voice distress/safety/calling.

VHF channel 70: 156.525 MHz, DSC distress and routine.

MF 2182 kHz: voice distress/safety.

MF 2187.5 kHz: DSC distress.

HF 4125, 6215, 8291, 12290, 16420 kHz: voice distress/safety.

HF DSC distress frequencies: 4207.5, 6312, 8414.5, 12577, 16804.5 kHz.

NAVTEX: 518 kHz international, 490 kHz national, 4209.5 kHz.

SART: 9 GHz (X-band radar).

Radio check: call a coast station or another vessel on a working channel, not channel 16; use low power.

Format: '[station called] THIS IS [your vessel and call sign], RADIO CHECK, OVER.' Reply: 'RADIO CHECK, RECEIVED YOU LOUD AND CLEAR' or 'WEAK BUT READABLE'.

DSC test: use the self-test function; do not send a live distress alert as a test.

EPIRB test: use the self-test function; do not activate the live transmission.

SART test: use the test function if available; do not activate in port.

Record tests in the radio log where required.

Test the reserve battery and emergency antenna regularly.

Check the antenna and coax for corrosion and damage.

A1: VHF DSC coverage; requires VHF DSC, EPIRB, MSI receiver.

A2: MF DSC coverage; requires MF/HF DSC or Inmarsat.

A3: Inmarsat coverage; requires Inmarsat or HF DSC.

A4: polar regions; requires HF DSC.

A vessel must be equipped for the highest sea area it enters.

MSI via NAVTEX or Inmarsat EGC.

Locating devices (SART, AIS-SART) for larger vessels.

Reserve source of energy for radio equipment.

Listen before transmitting; do not interrupt existing traffic.

Use standard phraseology: OVER, OUT, ROGER, WILCO, STANDBY.

Keep transmissions brief; identify with vessel name and call sign.

Do not use channel 16 for routine calls; move to a working channel.

Respect privacy; do not divulge personal information over the air.

Do not transmit profanity or offensive language.

Do not transmit without identification.

Switch ATIS on/off as required when crossing between inland and sea areas.

EPIRB battery life: typically 48 hours at -20 °C; check expiry date and replace before expiry.

EPIRB self-test monthly; do not activate live transmission for a test.

Register the EPIRB with the national authority; update details when the vessel changes owner, flag, or MMSI.

SART battery life: typically 96 hours standby, 8 hours operation; check expiry date.

SART should be mounted at least 1 m above sea level and switched on only in an emergency.

AIS-SART transmits position and identity on AIS; it appears on AIS displays.

Keep the EPIRB and SART in a float-free bracket or readily accessible location.

Test the EPIRB and SART before departure where possible.

DSC distress alert: lift the cover, press and hold DISTRESS for ~5 seconds; the alert is transmitted on channel 70.

The alert contains the vessel MMSI, position and time (from GPS if connected).

After the DSC alert, transmit the MAYDAY voice call on channel 16.

The coast station acknowledges by DSC and voice; await instructions.

If no acknowledgement, repeat the DSC alert or use other means (Inmarsat, HF, EPIRB).

A distress alert can be relayed by another station (MAYDAY RELAY).

False alerts must be cancelled immediately by DSC and voice.

Distress alerting is free of charge and has priority over all other traffic.

Channel selector: choose the correct channel for the purpose; channel 16 for distress/safety/calling, channel 70 for DSC only.

Squelch: set just above the point where background noise stops; it suppresses noise between transmissions.

Volume: controls audio loudness only; it does not affect transmission.

High/low power: use low power (typically 1 W) for short-range working; high power (25 W) only when needed.

Dual watch: monitors channel 16 plus one selected channel; tri-watch monitors 16, the selected channel and channel 70.

PTT (push-to-talk): press to transmit, release to receive; do not transmit without an antenna connected.

ATIS: required on inland waterways in some countries; must be disabled at sea.

Battery: charge fully before departure; carry spare batteries for handhelds.

Ship Radio Licence: issued by the flag state; authorises the use of the radio equipment on board; must be kept on board.

Operator certificate: SRC for VHF; LRC for HF; GOC/ROC for commercial vessels.

The licence specifies the equipment, the MMSI, and the call sign; changes must be notified.

Radio silence: 'SILENCE MAYDAY' or 'SILENCE DISTRESS' imposes silence; 'SILENCE FINI' lifts it.

Distress traffic has absolute priority; all other transmissions must cease.

Do not transmit false or deceptive distress signals; this is a criminal offence.

Keep a radio log where required; record distress, urgency, safety traffic and equipment malfunctions.

Use of non-type-approved equipment can invalidate the licence and is an offence in many countries.

VHF DSC watch on channel 70 must be maintained continuously when the radio is on.

NAVTEX receives MSI on 518 kHz (international), 490 kHz (national) and 4209.5 kHz.

406 MHz EPIRB alerts are routed to an RCC via Cospas-Sarsat; the RCC coordinates SAR.

SART and AIS-SART are locating devices; AIS-SART transmits on AIS frequencies.

VHF handhelds typically 5 W; check charge before departure and carry spare batteries.

Distress frequencies: VHF channel 16 (voice) and channel 70 (DSC); MF 2182 kHz (voice) and 2187.5 kHz (DSC); HF 4125, 6215, 8291, 12290, 16420 kHz (voice).

Radio checks should be made with a coast station or another vessel on a working channel, not on channel 16, using low power.

Reserve source of energy (battery) for radio equipment must be charged and tested regularly.

Listen before transmitting on a channel to avoid interrupting existing traffic, especially on channel 16.

Use standard phraseology: OVER (invitation to reply), OUT (end of communication), ROGER (received), WILCO (will comply), STANDBY.

Keep transmissions brief; identify with the vessel name and call sign at the start and end of the communication.

Do not use channel 16 for routine calls; make initial contact, then move to a working channel.

Respect privacy: do not divulge personal information over the air; remember that anyone can listen.

Use the correct channel for the purpose: 16 for distress/safety/calling, 06 for inter-ship, 13 for bridge-to-bridge, 70 for DSC only.

If you hear a distress call, do not transmit unless you can assist or are acknowledging; keep the channel clear.

Switch off ATIS when leaving inland waterways and entering sea areas, and switch on when entering inland waterways where required.