VHF DSC Radio Operation - Distress Calls & Routine Comms

Prerequisites

Before this lesson you should:

• Have the basic VHF awareness taught on RYA Competent Crew: how to switch on, select Channel 16 and send a basic Mayday if the skipper is incapacitated.
• Know how to give a position as latitude and longitude, and as a bearing and distance from a charted feature (Day Skipper chartwork).
• Know the difference between distress, urgency and safety situations in general terms (Competent Crew safety lessons).

Legal note: to operate a VHF or VHF DSC radio on a UK vessel you must hold at least the RYA/Ofcom Short Range Certificate (SRC), or be under the direct supervision of someone who does. The SRC is a separate course (about one day, including a practical assessment and a short written test, minimum age 16 for the authority to operate). The RYA expects a Day Skipper to be competent on the radio; the SRC is also required for commercial endorsement. This lesson covers the whole SRC syllabus at the depth the RYA expects, and is the radio side of skippering, but reading it does not replace the assessed course.

Learning Objectives

By the end of this lesson you will be able to:

• Explain the role of VHF and DSC within GMDSS, the four sea areas, and the three legal requirements (type approval, Ship Radio Licence, operator's certificate).
• Explain what an MMSI is, how the four types are recognised, and why it must be correct.
• Describe the VHF band, simplex and duplex working, and select the right channel for distress, safety, calling, intership, port operations, marinas and Coastguard liaison.
• Use the controls of a VHF DSC set, including squelch, dual watch, power selection and the Channel 16 button, and explain how aerials and height determine range.
• Use prowords, the phonetic alphabet and the correct form of positions, bearings, distances and times.
• Make a routine voice call and a DSC individual call, carry out a radio check and a DSC test call, and apply the rules for unanswered and garbled calls.
• Send a DSC distress alert with position entered automatically or manually, follow it with a Mayday voice call, respond correctly to an alert you receive, send a Mayday Relay and cancel a false alert.
• Make Pan-Pan and Securite calls, obtain medical advice through the Coastguard, and recognise the silence prowords.
• Receive Maritime Safety Information by VHF and NAVTEX, and describe EPIRBs, PLBs, SARTs and the actions on a false EPIRB alert.
• State the radio regulations: forbidden transmissions, secrecy of correspondence, control of communications and the radio log.
• Describe the format of the SRC assessment and answer exam-style questions.

RYA syllabus items covered: Day Skipper shorebased and practical VHF awareness; the full CEPT Short Range Certificate syllabus (RYA G26) sections A (general principles of the maritime mobile service), B (VHF installation and DSC), C (GMDSS procedures, protection of distress frequencies, MSI, alerting and locating signals) and D (regulations and radiotelephone procedure).

GMDSS, DSC and the Licences

What GMDSS is

The Global Maritime Distress and Safety System (GMDSS) was introduced by the International Maritime Organisation (IMO) in 1992, and fully implemented in 1999, after a century in which ships were still being lost without anyone hearing a distress call. It uses automated radio and satellite technology so that a distress alert reaches a Rescue Co-ordination Centre (RCC) and nearby vessels quickly and reliably, by two independent means, without a specialist radio operator on board. Pressing a single red button sends a digital alert that gives both the identity and the position of the casualty in a few seconds.

GMDSS is compulsory for commercial vessels over 300 gross tons, for passenger ships carrying 13 or more passengers and for fishing vessels. These "compulsory fit" ships must carry VHF DSC (plus MF or HF DSC outside Area A1), a 406 MHz EPIRB, a SART, radar, NAVTEX and waterproof handheld VHF sets. Yachts are "voluntary fit": they do not have to carry a radio at all, but if they do, they must use the GMDSS procedures and are strongly encouraged by HM Coastguard to fit DSC.

Sea areas are defined by coverage:

The whole of the UK coast is Sea Area A1 and, from the Scottish and Irish coasts, much of the surrounding sea is A2. A Day Skipper normally sails entirely within A1.

Digital Selective Calling (DSC)

DSC is a short digital data burst sent on VHF Channel 70. It acts as a "front end" or pager for the voice radio: it lets your set send an automatic alert, or call a particular station, without anyone needing to hear a voice. A distress alert carries your identity (MMSI), position from the connected GPS, the time of the position and, if you select it, the nature of distress. It sounds an alarm on every DSC radio and coast station in range and switches their sets to Channel 16 ready for your voice message. Channel 70 is for digital signals only: it must never be used for voice, and on modern sets it cannot be.

Seven classes of DSC controller exist. Class A and B are the full-specification sets on compulsory-fit ships; Class D is the minimum specification for VHF DSC on leisure craft and is the one covered here. Every Class D set must be able to send a distress alert, an all-ships call and an individual call; use the distress, urgency, safety and routine priorities; send the nature of distress, the distress position and the time of the position; propose a working channel; receive acknowledgement of its own distress alerts; receive individual calls and distress relays; and have a display and an alarm. Within those rules the menus differ from maker to maker, which is why the SRC assessment is done on a simulator and you must learn your own set.

The three legal requirements

When a VHF is fitted the owner must satisfy three requirements:

1. The equipment must be type approved. Sets sold in the UK carry a conformity mark and a Declaration of Conformity showing they meet the European Radio Equipment Directive. A set bought abroad, particularly in the USA, may lack the international channels, be illegal to use here and can be confiscated during an Ofcom inspection.
2. The equipment must be licensed. Under the Wireless Telegraphy Act every vessel fitted with radio equipment must hold a Ship Radio Licence.
3. The operator must be qualified, or be under the direct supervision of someone who is.

The Ship Radio Licence must be carried on board, and foreign authorities inspect it more often than Ofcom does. Using a radio without a licence or certificate is an offence and could affect your insurance. Candidates who hold the pre-2000 Restricted (VHF only) certificate may still use non-DSC sets but must take a conversion course or exam for the SRC before using DSC. For voyages beyond Area A1 using MF, HF or satellite equipment, the Long Range Certificate (LRC) is needed instead.

Who may use the radio. Any member of the crew may make routine calls under the supervision of the certificate holder, and the Day Skipper's safety briefing must ensure that everyone can send a distress alert and Mayday. A distress alert is sent on the authority of the skipper (the master of the vessel), not the radio operator.

The MMSI

The Maritime Mobile Service Identity is a nine-digit number programmed into a DSC radio. It identifies the vessel in every DSC call, just as a telephone number identifies a phone.

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• The MMSI is issued free with the Ship Radio Licence and linked to your vessel and emergency contacts in the national database held by Ofcom and available to the Coastguard. When a distress alert arrives, the Coastguard can look up who you are, your boat's description and whom to telephone.
• Many radios allow the MMSI to be entered only once; after that a dealer must reset it. Get it right: a wrong number sends rescuers looking for a different boat. The set should be programmed before you need it.
• Group MMSIs are programmable by the user but the number itself must be allocated by Ofcom.
• Coast station MMSIs are listed in the almanac; a searchable list of ship stations is kept by the International Telecommunication Union (ITU). If a vessel is not listed you must ask the owner.
• EPIRBs and PLBs use a separate identity (a hex ID) and must be registered with the UK Beacon Registry at Falmouth. Registration is a legal requirement.
• If you sell the boat, the licence and MMSI must be updated.

The VHF Band and the Channel Plan

Frequencies, simplex and duplex

The international maritime mobile band runs from 156.0 to 174.0 MHz and is divided into 59 international channels with 25 kHz spacing, plus some private channels allocated nationally. Each channel is allocated to one or more of eight purposes: distress, safety and calling; intership; bridge-to-bridge; port operations; ship movement; public correspondence; digital selective calling; and (in the UK only) small craft safety. Choosing the right channel for the purpose is a core part of the SRC.

• Simplex: one frequency, one direction at a time. You press the transmit switch to talk and release it to listen. All small-craft sets work this way, and all intership channels are simplex: two ships cannot talk on a duplex channel.
• Duplex: two frequencies, so both stations can talk at once, as on a telephone. Ship-to-shore working channels are allocated in pairs; on Channel 26, for example, the ship transmits on 157.300 MHz and the coast station on 161.900 MHz. A simplex set can still use a duplex channel; the press-to-transmit switch selects the right frequency, but only one station can speak at a time.
• Semi-duplex: simplex at one end and duplex at the other, which saves the shore operator having to release the switch.

The channels you must know

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Yacht clubs and marinas are not licensed for Channel 16, so the initial call to them is made on their working channel. Port authorities monitor Channel 16 and their own channels; make the initial call on the port channel listed in the almanac and use 16 only as a last resort. In UK harbours a radiotelephone may be used only for port operations and on licensed private channels; use the mobile phone, not the VHF, to arrange supper with the boat two berths down.

Power

The maximum permitted output for a small-craft VHF is 25 watts, and sets have a low-power setting of about 1 watt. Many sets select 25 watts when switched on. Except in an emergency, select 1 watt before transmitting whenever the station is close, because low power transmits over a shorter range and does not block the channel for everyone else within 25 miles. Use the minimum power that gives satisfactory communication.

The Equipment

Controls

A typical VHF DSC set has:

• On/off and volume. Turn up until background hiss is heard, then set the squelch.
• Squelch. Adjusts the threshold at which the receiver opens. Turn it just far enough to silence the hiss; too far and you will not hear weak, distant stations, which could include a Mayday.
• Channel selector and keypad, with a Channel 16 button that selects 16 immediately without using the keypad. Before sending a distress call make a positive check that the set really is on 16; dual watch can fool you into thinking it is because you are hearing Channel 16 traffic.
• Press-to-transmit switch on the fist microphone. While it is pressed you cannot hear anything. Lives have been lost because an inexperienced operator held it down and never heard the reply.
• High/low power switch (25 W or 1 W).
• Dual watch (D/W), which monitors Channel 16 and one other channel: the receiver sits on the chosen channel and switches to 16 whenever a transmission is detected there. Triple watch adds a second channel. Scanning steps through any number of selected channels, but gives no priority to 16, so a distress call can be missed, and it cannot scan Channel 70.
• The red DISTRESS button under a cover or sliding panel, so that it cannot be pressed by accident.
• The DSC screen and menu buttons, with ENTER (or CALL) for all DSC calls other than distress, and a log of received calls.

Installation

The set is mounted in the cabin, securely fastened, clear of spray and away from the engine and heat, with a waterproof extension speaker in the cockpit so the helm can hear it. It is wired to the ship's supply with the correct polarity; no earth is needed. On receive it draws very little current, but on transmit five amps or more, so make sure the battery can deliver it. Think about what happens if the vessel is sinking and the main batteries are flooded: a handheld with its own battery is the answer.

Aerials and range

VHF travels essentially in straight lines, so range depends mainly on aerial height, not on power. The diagram shows the principle.

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A useful approximation: range in nautical miles = 2.2 x (square root of aerial height A in metres + square root of aerial height B in metres).

• Yacht masthead aerial at 16 m (root 4) to a coast station aerial at 100 m (root 10): 2.2 x 14 = about 31 miles.
• Yacht aerial at 10 m (root 3.2) to a coast station at 100 m (root 10): 2.2 x 13.2 = about 29 miles. This is the SRC exam answer of 25 to 35 miles for alerting a coast station on Channel 70.
• Handheld at 2 m (root about 1.4) to another yacht's handheld at 2 m: 2.2 x 2.8 = about 6 miles.
• Handheld at 2 m to a coast station at 100 m: 2.2 x 11.4 = about 25 miles. A handheld reaches the Coastguard surprisingly well because the coast station aerial is high.

Two types of aerial are sold. A high-gain aerial, about two metres long, concentrates the signal in a narrow horizontal beam and gives greater range as long as it stays nearly vertical, so it suits motor cruisers. A unity-gain aerial, about a metre long, has a wider beam that is less affected by heeling and is recommended for sailing yachts, at the cost of a little range. Use low-loss coaxial cable with as few joins as possible, keep the feeder away from instrument and autopilot cables (even good cable radiates), and site the aerial at the masthead where it is not masked by the rigging. Carry an emergency aerial for the day you lose the mast. High pressure and humid air can extend range beyond normal; a rolling aerial in rough seas causes "fluttering" and shortens it. Hills and cliffs block the signal. Check connectors for corrosion: a poor connection can cut the range dramatically and a damaged aerial can burn out the transmitter.

Voice Procedure

The radio regulations

English is the international language of marine radio. Radio channels are never used for social chatter; all "traffic" should concern the safety or movement of vessels. The ITU lists transmissions that are strictly forbidden:

1. Profane, indecent or obscene language.
2. Unnecessary transmissions or superfluous signals (whistling into the microphone, discussing the football).
3. Transmissions without identification: the vessel's name must be given every time the microphone is keyed.
4. Broadcasting music.
5. False or deceptive distress, safety or identification signals.
6. Transmissions not authorised by the skipper.
7. Operation by an unauthorised person (crew may use the set under the supervision of the certificate holder).
8. Messages to an unlicensed shore station, such as a friend at home with a scanner or a handheld.
9. Personal names or unauthorised names instead of the vessel's name.
10. Closing down before finishing all operations arising from a distress call: if you have been involved in a rescue, you stay on watch until the Coastguard stands you down.
11. Use of channels not covered by the ship's licence.

Secrecy of correspondence. Anyone who overhears a radio conversation is legally bound not to divulge its contents, or even its existence.

Control of communications. Officially the station being called controls the communication and should name the working channel; when DSC is used, the caller chooses the channel. A coast station always controls communication with a ship. Obey instructions from a shore station, acknowledge any change of channel, and if told to stop transmitting, stay silent until released: the station may be handling distress traffic.

The radio log. Compulsory-fit ships keep a radio log; a yacht should record in the ship's log any distress, urgency or safety traffic heard, with times, and the Coastguard may ask for it.

Prowords

Prowords are standard words with fixed meanings that keep messages short and clear across language barriers. These are the ones the SRC examiner expects.

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Phonetic alphabet and numbers

Alfa, Bravo, Charlie, Delta, Echo, Foxtrot, Golf, Hotel, India, Juliett, Kilo, Lima, Mike, November, Oscar, Papa, Quebec, Romeo, Sierra, Tango, Uniform, Victor, Whiskey, X-ray, Yankee, Zulu.

Numbers are spoken digit by digit with the ITU pronunciations: WUN, TOO, TREE, FOW-ER, FIFE, SIX, SEV-EN, AIT, NIN-ER, ZERO. The decimal point is spoken as DECIMAL. 1430 is "one four three zero", 2.5 is "two decimal five", 7000 may be "seven thousand". Spell a difficult word by saying I SPELL, then the letters, then the word again if it can be pronounced: "intend anchoring off Youghal, I spell, Yankee Oscar Uniform Golf Hotel Alfa Lima, Youghal." A call sign is always spelled: "my call sign is Mike Bravo Delta Delta."

Positions, bearings, distances, speed and time

The IMO Standard Marine Communication Phrases (SMCP), which replaced the older Standard Marine Navigational Vocabulary, fix the way these are given:

• Position as latitude and longitude in degrees and minutes and decimals of a minute: 50 degrees 12.4 N, 001 degrees 27.7 W is spoken "five zero degrees one two decimal four minutes north, zero zero one degrees two seven decimal seven minutes west." Or as a bearing and distance from a well-defined charted object, the bearing in the 360-degree notation from true north: "my position is one eight zero degrees from Portland Bill lighthouse, two decimal four miles."
• Bearings of another vessel or mark are also in 360-degree notation from true north unless stated otherwise, and may be from the mark or from the vessel; say which. Relative bearings are given as degrees on the port or starboard bow.
• Distances in nautical miles or cables (tenths of a mile); if metres or kilometres are used, say so.
• Speed in knots; without further description it means speed through the water.
• Time in the 24-hour clock, stating whether it is UTC, local or zone time.
• Courses in 360-degree notation, true unless otherwise stated.

Good technique

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• Listen before transmitting; do not talk over someone. If the channel is busy, wait for a break.
• Think about what you will say before pressing the button, and write notes if the message is long. Keep a Mayday card by the radio.
• Hold the microphone about 8 cm from your mouth, a little to one side, shield it from wind, and speak at normal conversation level, a little slower and slightly higher pitched than usual. Do not drop your voice at the end of a phrase.
• Press the button, pause half a second, speak, finish, then release. Average reading speed is about 250 words a minute but writing speed is 20, so slow right down for anything the other station must write, such as a position.
• Keep messages short and use prowords, not slang ("ten-four" and "copy that" are CB, not marine). Use "I" and "you" carefully so there is no doubt who is meant.
• Say the vessel's name every time you key the microphone.

A routine call to another vessel (without DSC)

1. Switch on, set the squelch and volume, and select low power unless the other station is distant.
2. Select Channel 16 (or the working channel if you know the other vessel is keeping watch on it). Listen.
3. Call the other station's name twice (three times at most, in bad conditions) and your own name twice, and propose a working channel at once so that Channel 16 is cleared quickly.

"Seaspray, Seaspray, this is Blue Dolphin, Blue Dolphin, channel zero eight, over."

"Blue Dolphin, this is Seaspray, channel zero eight."

Both boats switch, and the caller makes the first call on the new channel: "Seaspray, this is Blue Dolphin on channel zero eight, over." "Blue Dolphin, Seaspray, pass your message, over."

Keep the conversation brief, then each station says its name and OUT. Return to Channel 16 and dual watch.

A routine call to a marina or harbour

Marinas listen on their working channel (normally Channel 80 in the UK), so call on that channel, say their name once and your own name twice:

"Hamble Point Marina, this is yacht Seawitch, Seawitch, over."

"Seawitch, Hamble Point Marina, go ahead, over."

"Hamble Point, Seawitch is a 10 metre yacht, 1.8 metre draught, requesting a visitor's berth for one night, ETA one five three zero, over."

"Seawitch, Hamble Point, berth Echo two six, port side to, over."

"Echo two six, port side to, Seawitch, out."

Port authorities that monitor several channels may not know which one you used, so say it: "Harwich Harbour Radio, this is Jasmine, Jasmine, on channel one two, over."

Readback

Read back anything important: positions, channel numbers, berth numbers, courses, times and instructions from the Coastguard or harbour authority.

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A readback proves you understood correctly and lets the sender correct you before an error matters. The marina example above shows a readback of the berth number. If the other station asks you to READ BACK, repeat the message prefixed by I READ BACK; they reply CORRECT or WRONG.

Unanswered and garbled calls

If a routine call gets no reply, first check your own set: power on, high power selected if the station is distant, volume up, squelch down, correct channel, and that the transmit button is not jammed. Then wait at least two minutes before calling again. You may call three times at two-minute intervals, after which you must wait three minutes before trying again. If another boat has not answered after two calls, it is probably not listening: stop calling and try later. Repeated unanswered calls are the commonest misuse of Channel 16.

If you hear a call but cannot tell who it is for, do not reply until it has been repeated and understood. If a call is clearly for you but you did not catch the caller's name, reply "Station calling Barbican, this is Barbican, say again, over."

Radio checks and test calls

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Check your radio regularly. Ask a marina, harbour office or another vessel on a working channel: "Hamble Point Marina, this is Seawitch, Seawitch, request radio check, over." The reply gives readability on a scale of 1 to 5, where 5 is perfectly readable ("loud and clear"). A voice test call must not exceed 10 seconds and must include your name. HM Coastguard discourages voice radio checks on Channel 16, which is a distress frequency.

The DSC function is checked with a DSC test call using the TEST category to a coast station's MMSI; HM Coastguard acknowledges these automatically, and this is now the preferred way to prove the whole DSC system works. Never test the system by pressing the distress button, and never make a voice transmission on Channel 70.

DSC Calls

DSC lets you call:

• Distress: an alert to all stations, sent with the red button.
• All ships: an urgency or safety announcement to everyone in range, before a Pan-Pan or Securite voice message. Sent with ENTER, not the red button.
• Individual: a specific MMSI (another yacht, a marina or a coast station), proposing a working channel. The other radio rings and switches channel automatically when accepted.
• Group: a predefined group MMSI, such as a flotilla or club.

Some sets also offer a position request or polling call to a friend's radio, a geographical area call, and the test call described above.

Making an individual DSC call step by step

An individual routine call saves everyone from listening to a call on Channel 16 and is the normal way to contact a marina, a harbour authority or another yacht whose MMSI you know.

1. Check the radio is on, set to the correct power for the distance (25 W for longer range, 1 W for close harbour work) and the squelch is set so that background hiss just disappears.
2. Press the CALL or MENU button and select INDIVIDUAL. Enter the MMSI of the station you are calling, or select it from the directory.
3. Select the category ROUTINE and the working channel you propose, for example Channel 72 for intership, or the channel used by the harbour authority.
4. Press ENTER to send. The call goes out as a data burst on Channel 70. If the other station accepts, both radios switch automatically to the working channel and you proceed with voice, starting with the station name.
5. At the end of the conversation, say your name, the other station's name and OUT, and return to Channel 16 (the radio's dual watch resumes on Channels 70 and 16).

If the other station does not respond, the set will tell you; wait and try again later. If you do not know the MMSI you call on Channel 16 by voice. Keep a list of the MMSIs you use most often in the radio directory, and store the group MMSI if you sail with a club or flotilla.

Incoming calls

An incoming routine call sounds the alarm and shows the caller's MMSI, and the name if it is in your directory. Press ACCEPT (or ENTER) to acknowledge digitally and the set switches to the proposed channel; you then answer by voice. All incoming calls are stored in the log, so you can see that you were called while you were on deck and could not hear the alarm.

Position and time

If a GPS is connected, the set shows your position and the time, and includes them automatically in a distress alert. If no GPS is connected, or the signal is lost, you must enter the position and time manually, at least every four hours and ideally every hour. A position more than about 24 hours old is deleted by the set and the alert goes out without one, which means the Coastguard knows who you are but not where. Check the screen each time you go on watch; if it shows dashes or nines, update it.

Dual watch and watch-keeping

A fixed DSC radio keeps a continuous watch on Channel 70 for DSC calls whatever voice channel is selected, and dual watch adds Channel 16. The SRC expects you to maintain an appropriate listening watch on DSC and voice: while you are at sea keep watch on 16, particularly in busy waters, and where practicable on 13 near shipping. The radio sounds an alarm for incoming alerts, so check the volume and the speaker is not turned down too low. Remember that while you are transmitting you cannot receive, which is one reason a distress alert is repeated automatically.

Maritime Safety Information (MSI)

HM Coastguard broadcasts navigational warnings, gale and strong wind warnings, the shipping forecast and the inshore waters forecast at scheduled times, typically every three hours, with a new forecast every six hours. Each broadcast is announced on Channel 16 ("All stations, all stations, all stations, this is Solent Coastguard... for maritime safety information listen channel six four") and then read on a working channel, commonly 62, 63, 64 or 10 depending on the station and your position. New gale warnings are announced on receipt with a Securite prefix. Small craft safety messages are also passed on Channel 67. The schedule and channels are in the almanac. Other European Rescue Centres use different channels; consult the almanac before going abroad.

NAVTEX is the GMDSS text service. Transmitters around the world broadcast on 518 kHz in English (and on 490 kHz in the local language; in the UK 490 kHz carries the inshore waters forecast and outlook) at allocated time slots so that they do not interfere with each other. A small receiver with a low aerial on the pushpit or coachroof (there is no advantage in height at medium frequency) prints or displays navigational warnings, gale warnings, weather forecasts, SAR information and warnings about aids to navigation out to about 300 miles. You programme the receiver to accept only the station letters and message categories you want, but you cannot reject navigational warnings, gale warnings or SAR messages. NAVTEX is one-way: it cannot be used to request information or send reports.

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Image: K. Krallis, SV1XV, CC BY-SA 3.0, via Wikimedia Commons

Other Distress Devices and the Link with VHF

A DSC radio is one of several layers of safety:

• EPIRB. A 406 MHz Emergency Position Indicating Radio Beacon is portable, battery operated, waterproof and buoyant. It transmits a coded distress alert through the COSPAS-SARSAT satellites, which pass it to the nearest RCC, giving worldwide coverage even when the VHF cannot be used or is out of range. The code contains the beacon's identity, which the UK Beacon Registry links to your vessel; registration is a legal requirement. Satellites fix a plain 406 beacon to within about two miles; a beacon with built-in GPS sends its position to within about 25 metres. A 121.5 MHz homing signal lets lifeboats and aircraft find you at close range. EPIRBs may be mounted on deck in a bracket with a hydrostatic release that floats them free if the boat sinks, or carried in the grab bag; either way they must be protected from accidental activation and inquisitive fingers. Check the battery expiry date and the hydrostatic release date, and test monthly using the built-in self-test only.
• PLB and AIS MOB beacons. A Personal Locator Beacon is a small 406 MHz beacon registered to a person; it is activated by hand and must be held clear of the water. AIS MOB beacons and DSC MOB devices alert the yacht's own AIS display and DSC radio when a crew member falls overboard; check that the MMSI in the device matches the radio.
• SART. A Search and Rescue Transponder responds to any 3 cm (X-band) radar within range with a line of 12 dots on the ship's radar screen, leading to the liferaft. It is a homing aid, not an alerting device, so it complements the EPIRB. Mount it as high as possible, at least a metre above the sea; held in a liferaft it is detected by a ship at about 5 miles and by an aircraft at 3,000 feet at up to 30 miles. The battery lasts about 96 hours. An AIS-SART does the same job by sending an AIS position to nearby vessels. A SART activated by accident must be reported to the Coastguard at once, in case a passing ship has seen the echo and started a search.
• Handheld VHF. A waterproof handheld with DSC and GPS is valuable if the fixed set fails or you leave the yacht. Keep it charged, in the grab bag, and with its MMSI programmed. Charge batteries as the maker recommends and keep a spare battery pack.
• Mobile phone. Useful inshore to call 999 or 112 and ask for the Coastguard, and to call a marina, but no substitute for VHF: it cannot keep a listening watch on a distress channel, nearby vessels cannot hear your call, broadcast warnings do not reach it, and the rescue services cannot take a direction-finding bearing on it.

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Image: Reise Reise, CC BY-SA 4.0, via Wikimedia Commons

Common Faults and Radio Care

• No DSC position. The GPS is not connected or has lost signal. Without position the DSC alert is less useful: you must give your position by voice, and update the radio manually.
• Range seems poor. Check the aerial, the cable connectors for corrosion, and the VSWR if you have a meter. A damaged aerial can burn out the transmitter.
• Weak transmission. Do not rely on high power alone: antenna height matters more. A masthead aerial gives much better range than a pushpit one.
• Flat batteries. Radios draw little on receive but more on transmit; keep an emergency battery or a handheld in the grab bag, and know the voltage below which the set stops transmitting.
• Water ingress. Cover the set when washing down; handhelds should be rated IPX7 or better.
• Set apparently dead. Check the circuit breaker, the inline fuse and the battery isolator before condemning it.

Distress: Mayday

Definition

The 1979 Search and Rescue Convention defines distress as grave and imminent danger to a person, ship, aircraft or other vehicle, requiring immediate assistance. Examples: sinking, fire out of control, a person overboard not immediately recovered, a life-threatening medical emergency, aground and breaking up, a vessel dragging towards rocks in a gale. The word MAYDAY (from the French m'aidez) is reserved for distress; it must never be spoken on the radio in any other context, even in conversation. If in genuine doubt, send it. The Coastguard would far rather downgrade a Mayday than arrive too late.

A distress transmission has three parts: the DSC distress alert, the voice distress call, and the voice distress message. A set without DSC uses only the last two.

Step 1: the DSC distress alert

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1. Check the main battery switch is on and the set is switched on.
2. Lift the cover over the red DISTRESS button and press it once.
3. If there is time, select the nature of distress from the menu (undesignated, fire or explosion, flooding, collision, grounding, listing or in danger of capsizing, sinking, disabled and adrift, abandoning ship, piracy, man overboard). If not, leave it undesignated.
4. Press and hold the button for five seconds, through the countdown, until the set confirms the alert has been sent.
5. The radio sends a data burst on Channel 70 containing your MMSI, your position (from GPS or manual entry), the time of the position and the nature of distress, then switches automatically to Channel 16. The whole process takes about 15 seconds.
6. The set repeats the alert automatically about every four minutes until a DSC acknowledgement is received on Channel 70 from a coast station, or until you cancel it. The screen shows the MMSI of the acknowledging station when one replies.
7. Wait about 15 seconds for the acknowledgement, then send the voice distress call and message on Channel 16 whether or not an acknowledgement has arrived: vessels without DSC will not have heard the alert, and the Coastguard needs the detail.

If no GPS is connected and you have time, type in the position and time before pressing the button, or give the position by voice immediately after.

Step 2: the voice Mayday on Channel 16

Use the structure below, which follows the RYA SRC format. Speak slowly and clearly: the person at the other end is writing it down.

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Notes:

• The call sign is given instead of the MMSI by a vessel without DSC. Some skippers give both.
• Give the position in the way most useful to rescuers. A bearing and distance from a well-known charted object is excellent; bearings are FROM the charted object TO you, in degrees true. Latitude and longitude from GPS is fine too, read digit by digit.
• The total number of persons matters because it decides the rescue method; do not waste time on adults and children.
• Write a pre-filled Mayday card with name, call sign and MMSI and fix it by the radio, with a gap for the position. The RYA procedure cards for DSC and non-DSC sets are the model.
• Release the transmit button and listen. If there is no response, repeat the call and message. If still none, try the handheld, another channel such as 6, 8 or 13 where someone may be listening, and the EPIRB.
• Once acknowledged, stay on 16 (or move as the Coastguard directs), keep the radio watch and give updates. Do not switch the set off until the incident is over.

The worked example shows a complete sequence.

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Acknowledgement

A coast station acknowledges a DSC alert digitally on Channel 70, which stops your set repeating it, then by voice on 16: "Mayday, Seawitch, Seawitch, Seawitch, MMSI two three five zero one two three four five, this is Solent Coastguard, Solent Coastguard, Solent Coastguard, received Mayday, launching lifeboat, stand by." A ship or yacht that hears a Mayday close to a coast station should wait a short time to let the Coastguard respond, then acknowledge by voice with RECEIVED MAYDAY and offer help if it can assist. A Class D set cannot acknowledge a distress alert digitally or switch off the alerting in another vessel's set; only a coast station or a Class A or B set can do that.

The obligation. The regulations say that the obligation to accept distress calls and messages is absolute for every station: they must be answered and action taken. In coastal waters the Coastguard is nearly always better placed, with lifeboats, helicopters and doctors, so a yacht should not clog Channel 16 with acknowledgements. But if you acknowledge, you are committing yourself to proceed to the casualty and help.

If you receive a distress alert

1. Your set sounds its alarm and switches to Channel 16. Read the MMSI, position and nature of distress on the screen, and write everything down. Tell the skipper.
2. Listen on 16 for the voice Mayday and write that down too.
3. Wait a short time (the SRC says about four minutes, or until the alert is repeated) to see whether a coast station acknowledges.
4. If a coast station acknowledges, keep listening, do not transmit unless asked, and be ready to help if requested.
5. If nobody acknowledges and the alert repeats, send a Mayday Relay (below). If you cannot and still nobody has answered, send a voice RECEIVED MAYDAY to the casualty and proceed to assist, continuing to try to raise the Coastguard.
6. Record the distress traffic in the log.

Mayday Relay

A station that learns of a vessel in distress sends a Mayday Relay when the casualty cannot send its own distress message, when a non-radio distress signal is sighted (flares, fire, flags, a person raising and lowering outstretched arms), or when a distress message has been heard that has not been acknowledged.

A Class D set has no Mayday Relay alert, so the DSC part of the procedure is an all-ships Urgency alert, which wakes every DSC set in range and switches it to Channel 16 without confusing the Coastguard's direction-finding, because an urgency alert carries no position. Some newer sets allow an individual DSC distress relay call addressed to a coast station's MMSI; use that if your set has it. Then by voice on Channel 16, making it quite clear that you are not the casualty:

"MAYDAY RELAY, MAYDAY RELAY, MAYDAY RELAY, this is motor yacht Bluebell, Bluebell, Bluebell, MMSI two three three zero zero zero two eight five. MAYDAY yacht Calamity, MMSI two three four zero zero one five two six, position five zero degrees four six minutes north, zero zero one degrees one seven minutes west, swamped in rough sea and sinking, require immediate assistance, five persons on board, abandoning to liferaft, time one four zero zero UTC, OVER."

Other vessels should not acknowledge a Mayday Relay unless they can help. For a light aircraft seen crashing nearby, or a capsized dinghy with someone waving, the correct DSC action is therefore an urgency alert followed by a voice Mayday Relay, not a distress alert from your own red button, because your vessel is not in distress.

Direction finding

Lifeboats and some SAR aircraft carry VHF direction finders and may ask you to transmit for a bearing: "Mayday, yacht Blaze, this is Portland Lifeboat, for direction finding purposes request you hold your press to transmit button closed for ten seconds followed by your name, repeat three times on this frequency, over." You reply "Mayday, Portland Lifeboat, this is yacht Blaze," press the button for ten seconds, say "yacht Blaze," and repeat the sequence three times. Several Coastguard stations also have VHF DF on Channel 16 and can sometimes give a yacht that is unsure of its position a bearing, but this is a bonus, not a service to rely on.

Radio silence

Each is broadcast in the form: MAYDAY, ALL STATIONS (three times), THIS IS (the station, three times), MAYDAY (name of casualty), the proword, the time, OUT. All stations aware of distress traffic but not taking part are forbidden to transmit on the channel being used until SEELONCE FEENEE is heard. Breaking imposed silence for non-distress traffic is an offence and can cost lives.

Cancelling a false alert

False alerts happen: a child presses the button, a set is tested wrongly, a cover is knocked. Cancel at once:

1. Let the alert complete once. If no acknowledgement has been received, switch the DSC equipment off to stop the repeats (or use the set's cancel function if it has one).
2. Switch back on and select Channel 16.
3. Make an all-stations voice broadcast giving your name, MMSI, position and the time of the alert, and confirm that the nearest Coastguard has received it:

"ALL STATIONS, ALL STATIONS, ALL STATIONS, this is yacht Seawitch, Seawitch, Seawitch, MMSI two three five zero one two three four five, in position five zero degrees three four decimal two north, zero zero two degrees two eight decimal one west, distress alert sent in error, cancel my distress alert of zero two four five UTC. OUT."

You will not be penalised for an honest mistake that you cancel promptly. Failing to cancel wastes rescue resources and may divert a lifeboat from a real casualty.

False EPIRB alert. Do NOT switch the 406 EPIRB off. Report the false alert to the nearest Coastguard, relaying through another station if necessary, giving your position and the beacon's identity, and switch it off only when told to. Switching off first can leave the RCC searching for hours for a beacon that has gone quiet. For a SART or an old 121.5 MHz beacon activated by accident, switch it off, broadcast an all-ships message on 16 giving the position, and inform the Coastguard.

Urgency: Pan-Pan

Pan-Pan is for a serious situation concerning the safety of a vessel or person where the danger is not yet grave and imminent: a boat taking on water but not yet sinking, engine failure with no other means of propulsion some distance from a lee shore, a dismasting with no immediate risk, an injury that needs treatment but is not life-threatening, or urgent medical advice. Anything less than distress may justify an urgency call, and an urgency situation can always be upgraded to distress.

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1. DSC: select ALL SHIPS, then URGENCY, and press ENTER; the set asks you to confirm because an all-ships alert switches every set in range to Channel 16. Your radio switches to 16. An urgency alert contains your MMSI and the time but no position, so the position must be in the voice message.
2. Wait about 15 seconds, then by voice on 16, addressed to ALL SHIPS, ALL STATIONS or to a named Coastguard station:

"PAN-PAN, PAN-PAN, PAN-PAN, Falmouth Coastguard, Falmouth Coastguard, Falmouth Coastguard, this is motor yacht Unfortunate, Unfortunate, Unfortunate, MMSI two three four zero zero one five four six, my position is four nine degrees three eight decimal four five north, zero zero six degrees two zero decimal one four west, total engine failure and drifting, I require assistance to clear the traffic separation scheme, two persons on board, hull black, upperworks white, OVER."

The nearest coast station acknowledges by voice if within range, may repeat the Pan-Pan on 16, and takes control of further traffic. If the situation worsens, upgrade to Mayday. When it is resolved, cancel the Pan-Pan with an all-stations message so that nobody keeps looking for you.

Medical advice. Urgent medical advice is obtained through any HM Coastguard Rescue Centre by a DSC urgency alert and a Pan-Pan voice call (the older term Pan-Pan Medico is still heard abroad). The Coastguard links you to a doctor, usually on a working channel, and can arrange evacuation by lifeboat or helicopter if the doctor advises it.

Safety: Securite

Securite (pronounced say-cure-ee-tay) introduces a message about the safety of navigation or an important meteorological warning: a drifting container or hulk in a shipping lane, a buoy off station or unlit, a gale warning. It is normally sent by the Coastguard, and only rarely by a yacht, for instance after sighting a semi-submerged container in a busy area.

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1. DSC: select ALL SHIPS, then SAFETY, confirm and press ENTER. The safety alert is less strident than the others; receiving sets show that a safety alert has arrived and should be ready to write down the message.
2. By voice on Channel 16, announce the working channel on which the message will follow, then move to it and read the message:

On 16: "Securite, Securite, Securite, all stations, all stations, all stations, this is Humber Coastguard, Humber Coastguard, Humber Coastguard, for urgent navigational warning listen channel six seven, out."

On 67: "Securite, Securite, Securite, all stations, all stations, all stations, this is Humber Coastguard, Humber Coastguard, Humber Coastguard, large drifting hulk reported in position five one degrees four zero minutes north, zero zero one degrees one zero minutes east, considered a danger to surface navigation, time of origin one two three zero UTC, out."

Stations hearing the safety call switch to the working channel and listen until they are sure the message does not concern them, without transmitting anything that could interfere. The order of priority on the radio is always Mayday, then Pan-Pan, then Securite, then routine.

Coastguard Liaison

All HM Coastguard Rescue Centres keep a constant watch on DSC Channel 70 and a loudspeaker watch on Channel 16. Channel 67 is the UK small craft safety channel for exchanging safety information that does not justify distress or urgency procedures; the Coastguard will usually ask you to move there. The Coastguard welcomes passage information from small craft on longer trips (who you are, where you are going, when you expect to arrive) but has neither the staff nor the systems to track yachts from port to port, and will not start a search unless your shore contact reports you overdue. So nominate a shore contact, tell them your plan and your "panic time", and tell them when you arrive. The Coastguard's own voluntary identification scheme lets you lodge the boat's details and contacts in advance so that they are on file when your MMSI appears on a screen.

Finally, the MCA warns (MGN 167) against using VHF to negotiate collision avoidance between ships: identification is uncertain, misunderstanding is easy, and time spent on the radio is time not spent applying the COLREGs. A yacht should comply with the Rules and keep the radio for what it is for.

The SRC Assessment

The SRC is awarded after an assessed course at an RYA Training Centre, or by examination for those who do not attend a course. Assessment is continuous and has two parts.

Practical assessment on a DSC simulator, in which you must be able to: define a distress situation; initiate a DSC distress alert with position and time entered automatically or manually; send a Mayday by voice; respond correctly to a DSC distress alert and to a Mayday, including relaying a distress message; know how to deploy an EPIRB and a SART; cancel a distress alert sent in error; define an urgency situation, send a DSC urgency alert and a Pan-Pan, and respond to one; recognise a safety situation, send a DSC safety alert and a Securite; receive MSI by NAVTEX; make a DSC routine call; establish communication and exchange messages by voice on the right channels; test the set with an appropriate test call; enter a group and an individual MMSI; keep an appropriate listening watch; and use the phonetic alphabet.

Written test of 30 minutes. Part A covers distress and urgency procedures, with a question that asks you to write out a full distress call and message for a given scenario; Part B is a set of short general questions on channels, MMSIs, phonetics, controls, NAVTEX, EPIRBs and SARTs, forbidden calls, prowords and licensing. A pass is required in both parts.

What examiners look for: a calm, correctly ordered Mayday from memory; the position spoken slowly in the right form; low power selected for close work; the right channel for each purpose; no "over and out"; the word MAYDAY used only for distress; and a candidate who knows what to do when an alert is received, not only how to send one.

Worked Example

Scenario

You are skipper of the yacht Seawitch (MMSI 235012345, call sign MGAB4), 4 miles south of a headland, with four on board. A crew member has slipped down the companionway and has a suspected broken leg. She is conscious and breathing normally but in severe pain. Wind southwest Force 4. You are 2 hours from harbour.

1. Decide the priority. The injury is serious and needs medical help, but life is not in immediate danger. This is a Pan-Pan, not a Mayday.
2. DSC: send an All Ships Urgency alert (ENTER, not the red button), or an individual call to the Coastguard's MMSI with the category URGENCY.
3. Voice on 16, after 15 seconds: "Pan-Pan, Pan-Pan, Pan-Pan, all stations, all stations, all stations, this is yacht Seawitch, Seawitch, Seawitch, MMSI two three five zero one two three four five, position one eight zero degrees true from (headland), four miles, crew member with suspected broken leg, conscious and breathing, require medical advice and assistance, four persons on board, OVER."
4. The Coastguard replies and moves you to Channel 67, and links a doctor. You give the details and read back the advice: "Immobilise leg, keep her warm, no food or drink, continue towards (harbour), ETA one five three zero, lifeboat will meet us at the harbour entrance, Seawitch, over."
5. Twenty minutes later the casualty becomes drowsy and her breathing is shallow. The situation is now grave and imminent: you upgrade to Mayday on 16 (or on 67 if the Coastguard has told you to stay there), giving the updated position.
6. When the lifeboat has taken her off and the Coastguard says "Seelonce Feenee" and stands you down, you log the times and messages, and only then return to normal working.

Common Mistakes

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• Chatting on Channel 16. Call, then move to a working channel. Social chatter belongs on the phone.
• Forgetting to cancel an accidental DSC alert, or switching off an accidentally activated EPIRB before telling the Coastguard.
• Voice on Channel 70. It is digital only.
• Pressing the red button for an urgency or a relay. The red button means your own vessel is in distress. Urgency, safety and Mayday Relay alerts go out with ENTER.
• No GPS link to the DSC radio, so alerts go without a position. Check the radio shows your position, and enter it by hand if it does not.
• Giving a bearing TO the headland instead of FROM it. Bearings in a position report are from the charted object to you, in degrees true.
• Saying "over and out", "roger wilco" or "repeat" when you mean "say again".
• Transmitting on 25 watts to the marina 200 metres away, and then not hearing its 1 watt reply.
• Calling again and again without waiting two minutes, or leaving dual watch and assuming the set is on 16.
• Waiting too long to call. Call early; a Pan-Pan that becomes a Mayday is better than a Mayday that comes too late.
• No handheld backup, or one with a flat battery.
• No procedure card by the set, so that the one person who knows the drill is the one who has just gone overboard.

Summary

• GMDSS gives a casualty two independent means of alerting an RCC. Yachts are voluntary fit but must use GMDSS procedures. The UK coast is Sea Area A1.
• Three legal requirements: type-approved equipment, a Ship Radio Licence (Ofcom, free online, ten-year revalidation, carried on board) and an operator with an SRC or under their supervision. Handhelds used on several boats need a Ship Portable Radio Licence.
• The MMSI identifies your vessel: ships start with the country MID (232 to 235 for the UK), coast stations with 00, groups with 0. Program it once, correctly, and link the radio to GPS.
• Channel 16 voice distress and calling; 70 DSC only; 67 UK small craft safety; 6, 8, 72 and 77 intership; 13 bridge-to-bridge; 80 marinas; M and M2 clubs; port channels per the almanac. 25 W maximum, 1 W whenever possible.
• Range depends on aerial height: 2.2 x (root of each height in metres). Unity-gain aerials for sailing yachts, masthead mounted, low-loss cable.
• Use prowords, the phonetic alphabet and readbacks; positions as lat and long or a true bearing and distance FROM a charted object. Wait two minutes before repeating an unanswered call.
• Distress: red button five seconds (select the nature if there is time), wait 15 seconds, then voice Mayday on 16 in the standard order. The set repeats the alert every four minutes until acknowledged.
• On receiving an alert: write it down, wait for the Coastguard, relay with an urgency alert and voice Mayday Relay if nobody answers, and only acknowledge if you can help.
• Urgency: Pan-Pan (no position in the DSC alert, so give it by voice). Safety: Securite, announced on 16 and passed on a working channel. Know Seelonce Mayday, Seelonce Distress, Prudonce and Seelonce Feenee.
• Cancel false DSC alerts immediately by voice on Channel 16; never switch off a false EPIRB until told to.
• EPIRBs alert through satellites and must be registered; SARTs guide radar-fitted rescuers; NAVTEX delivers MSI as text; mobile phones are a backup only.

Check Your Understanding

1. What three requirements must be satisfied before a VHF set is used on a UK yacht?

Answer: The equipment must be type approved (conformity marked), it must be covered by a Ship Radio Licence (or a Ship Portable Radio Licence for a handheld used on several craft), and it must be operated by, or under the direct supervision of, the holder of an operator's certificate such as the SRC. Call signs and MMSIs are allocated by Ofcom.

1. Which of these MMSIs belongs to a coast station, which to a group, and which to a ship: 002320014, 023376543, 234678546?

Answer: 002320014 is a coast station (two leading zeros); 023376543 is a group (one leading zero); 234678546 is a UK ship (MID 234).

1. What is Channel 70 used for, and what must you never do on it? On which channel is an urgency message sent by voice?

Answer: Channel 70 is for DSC digital alerts and calls only; never use it for voice (and never make voice test calls on it). The voice Pan-Pan is sent on Channel 16.

1. Estimate the range between a yacht aerial at 9 m and a coast station aerial at 64 m. Why does the squelch matter, and why use low power?

Answer: 2.2 x (3 + 8) = about 24 nautical miles. The squelch silences background hiss; set too high it hides weak distant signals, which could be a Mayday. Low power limits the range of your transmission so that it does not block the channel for others when the station you are working is close, and marinas themselves transmit on only 1 watt.

1. Write the distress call and message for the motor cruiser Hot Stuff, MMSI 232001457, on fire and about to abandon to the liferaft with three people on board in position 51 degrees 29.2 N, 001 degrees 42.7 E.

Answer: MAYDAY, MAYDAY, MAYDAY. This is motor cruiser Hot Stuff, Hot Stuff, Hot Stuff, MMSI two three two zero zero one four five seven. MAYDAY Hot Stuff. My position is five one degrees two nine decimal two minutes north, zero zero one degrees four two decimal seven minutes east. On fire and unable to extinguish, abandoning to liferaft. I require immediate assistance. Three persons on board. OVER.

1. A light aircraft crashes into the sea near your yacht, which has a Class D DSC set. What DSC alert and voice message do you send?

Answer: A DSC Urgency (all ships) alert followed by a voice MAYDAY RELAY on Channel 16. Your own vessel is not in distress, so you do not press the red button, and a Class D set has no Mayday Relay alert; the urgency alert wakes nearby sets without sending a misleading position.

1. You receive a DSC distress alert that is not acknowledged by the Coastguard. What do you do?

Answer: Write down all the details, inform the skipper, listen on Channel 16 for the voice Mayday, and wait a short time (until the alert repeats after about four minutes) for a coast station to acknowledge. If none does, send an urgency alert and a voice Mayday Relay; if that is impossible, send a voice RECEIVED MAYDAY and proceed to help, continuing to try to raise the Coastguard. Record everything in the log.

1. A crew member accidentally presses the red DSC button. What should you do?

Answer: Let the alert complete once, switch the DSC off (or cancel) to stop the repeats, switch back on, select 16 and broadcast "All stations x3, this is (name x3), MMSI..., position..., distress alert sent in error, cancel my distress alert of (time) UTC, out", then confirm the Coastguard has received the cancellation.

1. What do SEELONCE MAYDAY, PRUDONCE and SEELONCE FEENEE mean, and who may say each?

Answer: SEELONCE MAYDAY: all other stations keep silent; said only by the station controlling the distress traffic or the casualty (any other station nearby uses SEELONCE DISTRESS). PRUDONCE: restricted working may resume for urgent traffic; said by the controlling station. SEELONCE FEENEE: the distress traffic is over and normal working may resume; said by the controlling station.

1. Your engine has failed in light winds 2 miles off a lee shore, but you are not yet in danger. Which signal do you use, how is it sent, and what must the voice message include that the DSC alert does not?

Answer: Pan-Pan (urgency): a DSC all-ships urgency alert sent with ENTER, then after 15 seconds the voice Pan-Pan on Channel 16. The DSC urgency alert carries no position, so the voice message must give it. Upgrade to Mayday if the danger becomes grave and imminent.

1. What is NAVTEX, and what can it not do? With what should a DSC controller be interfaced?

Answer: NAVTEX is the GMDSS system for receiving gale warnings, weather forecasts, navigational warnings and SAR information as text on 518 kHz (490 kHz for local-language or inshore services) out to about 300 miles. It is receive-only: it cannot request information or send reports, and it is not weather fax. The DSC controller should be interfaced with the GPS so that the distress alert includes the position automatically.

1. You activate your EPIRB by mistake. What do you do, and how should a SART be deployed?

Answer: Do not switch the EPIRB off. Contact the nearest Rescue Co-ordination Centre (Coastguard), relaying through another station if necessary, give your position and the beacon identity, and switch off only when told to. A SART is mounted as high as possible, at least a metre above the sea, and responds to 3 cm radar; it is a homing aid, not an alerting device.

1. Which of these calls is permitted: a test call on Channel 70, a call to a yacht club on Channel 37, a broadcast of music to club boats, a call during distress working?

Answer: Only the call to the yacht club on Channel 37 (Channel M). Voice test calls on 70, broadcasting music and transmitting during imposed distress silence are all forbidden.

1. You call another boat on Channel 16 and get no reply. How long must you wait before calling again, and what should you check first?

Answer: At least two minutes (up to three calls at two-minute intervals, then a three-minute wait). First check your own set: power on, correct channel, volume up, squelch not too high, high power selected if the station is distant, and that the transmit button is not stuck.

1. Why should a DSC set's position be updated manually when no GPS is connected, and how often?

Answer: So that a distress alert carries a position; without one the Coastguard knows who is in distress but not where. Enter it at least every four hours (ideally hourly); a position more than about 24 hours old is deleted automatically and the alert goes out without one.