Marine VHF radio: MAYDAY distress call – basics

Marine radio uses internationally agreed channels and procedures so that coast stations, rescue coordination centres and other vessels can hear and understand a distress call – whatever country they come from. Channel 16 is internationally reserved for distress, urgency and safety traffic. Many vessels and coast stations listen to it constantly. So anyone calling MAYDAY on channel 16 reaches everyone listening within radio range.

VHF radio waves travel roughly in line of sight. The higher the antenna, the further the signal reaches – which is why large ships with tall masts and coast stations on hills reach further than a handheld on a kayak. An exact range cannot be stated in general; it depends on antenna height, transmit power, terrain and weather.

DSC (Digital Selective Calling) is an additional digital function. Pressing the distress button makes the radio send an automatic alert with the vessel's identity (MMSI) and – if a GNSS receiver is connected or built in – its position. A voice distress call on channel 16 in a fixed format follows.

The message follows a fixed format so nothing important is forgotten: 'MAYDAY, MAYDAY, MAYDAY – this is' and the vessel's name three times, plus call sign or MMSI; then 'MAYDAY' once more and the vessel's name; then position, nature of distress, assistance required, number of persons on board, other information – and finally 'OVER'. It helps to fix this format clearly visible next to the radio.

The position is the most important part – without it nobody can come. Read it from the navigation device or describe it as a bearing and distance from a known point, such as a lighthouse. Keep the vessel's name, call sign and MMSI at hand so you do not have to search for them under stress.

A radio cannot transmit and receive at the same time. As long as you press the transmit button, you hear nothing. Release it after the message and listen. If no reply comes, repeat the message at short intervals. Then follow the coast station's instructions, keep radio traffic short and conserve the battery.

There are three levels. MAYDAY means grave and imminent danger to people or the vessel – such as sinking, fire on board, person overboard. PAN PAN announces an urgent situation without immediate danger to life, for example an engine failure while the boat is still drifting safely. SÉCURITÉ introduces a safety message, for example about floating debris or a dangerous obstruction.

Anyone who hears a distress call that goes unanswered can pass it on as a MAYDAY RELAY. That can save lives when the vessel in distress is far from the coast and only you can hear it. Choosing the right level helps rescue services send their resources where they are needed most.

MAYDAY is only for grave and imminent danger. Misuse – such as a prank call or a false distress call – is a punishable offence in many countries, because it ties up rescuers and can drown out genuine distress calls. Non-urgent conversations do not belong on channel 16 either; there are other channels for them.

Operator certificates, equipment licences and channel use are regulated nationally. In many countries you need an operator certificate to use a marine radio – for recreational skippers often a short certificate after a course with an exam – and the radio itself must be licensed. Check local rules. This entry does not replace radio training. In a genuine emergency, however, anyone may generally send a distress call.

A handheld should be waterproof or carried on the body in a waterproof pouch, not loose in the boat. If you capsize, you will still have it with you. On land, a marine radio is no substitute for a phone emergency call – there, the local emergency number (112 in the EU) is the right route.

Marine radio is the standard tool on the water, but not the only one. A distress beacon (EPIRB on vessels, PLB on the body) raises the alarm via satellite even where there is no radio contact. A phone may have signal near the coast. Light signals, orange smoke, coloured cloths and slowly raising and lowering the arms help rescuers find you on the spot.

Rescuers can take radio bearings and so locate a radio. That is why it makes sense to stay reachable after a distress call and keep the radio switched on. Many countries offer short radio courses; there you practise the procedure until it works even under stress. A handheld carried on the body is a sensible complement to phone and PLB, even on small boats and kayaks.