Radio & technology

VHF marine radio & SRC

Voice radio on fixed channels — and why channel 16 stays clear.

VHF marine radio works on fixed channels with a range slightly beyond line of sight — depending above all on aerial height. Operating it requires a radio certificate: the SRC (Short Range Certificate) for coastal sailing with DSC, the LRC for worldwide voyages. Maximum transmit power is 25 W, switchable to 1 W at close range.

Important channels

Channel 16 — calling, distress and safety channel; kept clear and monitored.
Channel 70 — DSC only (digital calls), never voice.
Working channels — after calling on 16 you switch to a free working channel.

DSC — Digital Selective Calling

The distress alert at the push of a button on channel 70.

DSC (Digital Selective Calling) sends a short digital message on channel 70 — for instance a distress alert with your own identity (MMSI) and, with GPS connected, your position. The red, guarded distress button triggers the alert; the spoken mayday on channel 16 follows.

This requires an MMSI programmed into the set. DSC is also used for ordinary (routine) calls, in which one particular station is called selectively.

MMSI

The nine-digit identity of your radio.

The MMSI (Maritime Mobile Service Identity) is a nine-digit number that identifies a radio or vessel uniquely. It is issued once by the national authority and programmed into the DSC radio and, where fitted, the AIS. The first three digits (MID) stand for the country.

NAVTEX

Automatic reception of warnings and weather messages.

NAVTEX is an automatic radio service that receives navigational warnings, weather warnings and safety messages as text — internationally on 518 kHz in English, in places additionally on 490 kHz in the national language. The set runs in the background and stores the messages for the sea area you have selected.

AIS

Seeing other vessels and being seen.

AIS (Automatic Identification System) automatically transmits and receives vessel data — name and MMSI, position, course over ground (COG) and speed over ground (SOG). Other vessels appear as symbols on the plotter or app; many sets calculate CPA and TCPA (closest point of approach and the time to it) as a collision warning.

Commercial ships carry Class A, many pleasure craft use Class B. AIS replaces neither the lookout nor the radar — not every vessel transmits.

GPS & chartplotter

Satellite position — and its limits.

GNSS/GPS supplies position, course over ground and speed over ground continuously. The chartplotter shows the position on the electronic chart; routes and waypoints can be planned and followed.

Limits

Never rely on the plotter alone: chart data can be out of date or inaccurate, equipment fails, and the accuracy displayed suggests a certainty that is not there. Cross-check the position (bearings, sounding, landmarks) and carry a paper chart as a fallback.

Radar & radar reflector

Showing up on someone else's radar in the first place.

Small GRP boats give a weak radar echo. A passive radar reflector — or an active radar transponder — enlarges the echo considerably, so that others, commercial traffic above all, are more likely to see the boat. Mount it as high and as favourably as possible.

Your own radar helps in restricted visibility to measure range and course, and so to avoid collisions, but it does not replace the lookout.

Log & echo sounder

Measuring speed through the water and depth.

The log measures speed through the water and totals the distance run — the basis of dead reckoning. The echo sounder measures the depth by the travel time of sound. It matters to know what the sounder reads from: the surface, the keel or the transducer (offset).

Types of compass

Steering, taking bearings, measuring electronically.

There are several compasses on board:

Steering compass (magnetic) — permanently mounted, for steering; subject to deviation caused by the boat.
Hand bearing compass — for taking bearings on landmarks and lights.
Electronic or fluxgate compass — supplies heading data to autopilot and plotter.

The magnetic compass needs no power and is the independent fallback.

MAYDAY, PAN PAN, SÉCURITÉ

The three priority levels of voice radio — and how a distress call is built up.

MAYDAY (distress) — grave and imminent danger to vessel or life, immediate assistance required.
PAN PAN (urgency) — a serious situation without immediate danger to life, such as engine failure on a lee shore.
SÉCURITÉ (safety) — an important navigational or meteorological warning message.

Structure of the distress call

After the DSC distress alert (channel 70), the spoken distress call follows on channel 16:

MAYDAY, MAYDAY, MAYDAY — this is (vessel name, three times), call sign and MMSI.

Then the distress message: MAYDAY, vessel name — position — nature of distress — assistance required — number of persons on board — any other information.

For the position, remember: latitude first, then longitude — or a bearing and distance from a known point. Speak slowly and clearly; distress traffic takes priority over everything else, and everyone else keeps radio silence.

International phonetic alphabet

Alfa to Zulu — on the radio every name gets spelled out.

A Alfa · B Bravo · C Charlie · D Delta · E Echo · F Foxtrot
G Golf · H Hotel · I India · J Juliett · K Kilo · L Lima
M Mike · N November · O Oscar · P Papa · Q Quebec · R Romeo
S Sierra · T Tango · U Uniform · V Victor · W Whiskey · X X-Ray
Y Yankee · Z Zulu

Vessel names, call signs and anything that could be misheard are spelled out: 'I spell: Kilo, Echo, Echo, Lima …'. Numbers are spoken digit by digit, nine as 'niner'.

Important VHF channels

Channels 16 and 70 at sea, channel 10 on the river — who listens where.

Marine radio

Channel 16 — distress, urgency and safety traffic, and calling. Keep a listening watch whenever the set is on.
Channel 70 — DSC only (digital alerting), never voice.
Channels 06, 08, 72, 77 — ship-to-ship traffic, for instance between yachts.

Inland waterway radio

Channel 10 — nautical ship-to-ship traffic; keep a continuous watch while under way.
Channels 72 and 77 — social messages.
Traffic centres and locks have their own signposted channels.

ATIS (inland radio)

The automatic identification used on inland waterways.

On inland waterway radio the set automatically transmits its ATIS code (Automatic Transmitter Identification System) each time the transmit key is released. It is derived from the vessel's call sign and identifies every transmission uniquely — which is why inland stations need their own allocation and the set needs an inland mode.

In practice this means: on inland waters the radio must be switched to inland operation (ATIS active, reduced transmit power of normally 1 watt for ship-to-ship traffic).

Order of priority in radio traffic

Distress beats everything: the order in which messages take priority.

Messages on marine radio have a fixed order of priority:

1. Distress traffic (MAYDAY)
2. Urgency traffic (PAN PAN)
3. Safety traffic (SÉCURITÉ)
4. Routine traffic

Higher-priority traffic interrupts lower. While distress traffic is running, everyone else keeps radio silence until the controlling station lifts it.