Another means of calling for help at sea

In the last article we looked at using a marine VHF radio to call for help at sea. In this article we are going to look at another, supplementary means of distress alerting: Emergency Position Indicating Radio Beacons or EPIRBs.


The McMurdo SmartFind Plus G5 EPIRB (image courtesy of McMurdo Group)

What is an EPIRB?

An EPIRB is another means of alerting the Search and Rescue (SAR) authorities that you are in distress. It carries the same weighting as a DSC distress alert and/or voice Mayday message by radio. For large commercial and passenger carrying vessels that operate under GMDSS, it provides one of the two mandatory, independent means of distress alerting.

For all other vessels, including small commercial and leisure users, it is an alternative means of calling for help in an emergency, with the added bonus of worldwide coverage. The cost of these devices has come down in recent years and as a result, they are becoming commonplace on smaller vessels.

How does an EPIRB work?

When activated, an EPIRB works by transmitting a digital radio signal to one of the COSPAS-SARSAT network of polar-orbiting satellites. This system, a joint venture between the US, Soviet Union, Canada and France, was originally developed in the 1970s. Since its inception, it has been responsible for the rescue of over 39,000 people in over 11,000 incidents.[1]

Nowadays, all EPIRBs work on the 406Mhz frequency. Upon activation, the device will transmit a signal with a unique code, allowing SAR authorities to identify the vessel in question. It is therefore imperative that all EPIRBs are registered to the vessel on which they are located. In the UK, this is done through the Coastguard and in addition, the device must be declared on the Ship’s Radio Licence.

How do you activate an EPIRB?

SmartFind EPIRB_lifeRraft in Water (2)

In this situation, the McMurdo Smartfind G5 406Mhz EPIRB comes into it’s own (image courtesy of McMurdo Group)

EPIRBs can either be activated manually or automatically via the use of a Hydrostatic Release Unit (HRU). The latter method is mandatory for vessels operating under GMDSS and means the device will ‘float-free’ of a sinking vessel and automatically activate. The exact method of manual activation varies slighltly between manufacturers and it is crucial to be familiar with the model you use.

It is important to note that the latest advice with regards to accidental activation is to switch the EPIRB off immediately and contact the nearest coastguard or relevant authority as soon as possible.

How does an EPIRB provide your position?

Position information from an activated EPIRB can be delivered in one of two ways, depending on the model. Orbiting satellites can work out the location of the device using Doppler positioning. This relies on the principle that the frequency of the signal will change as the satellite moves over and based on the speed at which this changes, the satellite can work out how far away and in what direction the device lies. This method is accurate to within approximately 3 miles.

Alternatively, a newer generation of EPIRBs are available with a built-in GPS. When activated, these devices send a coded signal which includes their current position. This method is far more accurate, usually pinpointing the device to within approximately 50m.

What happens after an EPIRB signal is received?

When a satellite receives a signal from an EPIRB, it then relays to it one of the many earth stations dotted around the world. This signal is then passed onto the nearest Rescue Coordination Centre (RCC), who will launch the appropriate SAR service depending on the location of the casualty. If the signal has originated from a long way offshore, beyond the range of lifeboats and helicopters, then the RCC will normally turn to passing commercial traffic to effect a rescue.


Although all EPIRBs now transmit on the 406Mhz frequency, most devices also transmit a secondary signal on the older 121.5Mhz frequency. This allows SAR services, such as lifeboats and helicopters, to ‘home-in’ on the casualty using their radio direction finding equipment. In addition, EPIRBs normally float and have a bright, white flashing light, in order to aid location at night.

Personal Locator Beacons

McMurdo 220-PLB

I carry my McMurdo Fast Find 220 Personal Locator Beacon on my person at all times when at sea (image courtesy of McMurdo Group)

In recent years, the use of Personal Locator Beacons (PLBs) has become more common. These are in effect mini-EPIRBs; the difference being they are registered to an individual rather than a vessel. Small enough to be carried on your person, they operate on exactly the same system as the larger EPIRBs but generally with reduced battery life.

In addition, PLBs contain a built-in GPS, allowing very accurate position information to be included in any distress signal. In 2012, in line with other countries, the law was relaxed in the UK to allow the use of PLBs over land. It is important to note that unlike some EPIRBs, all PLBs have to manually activated by the user.

FastFind 220 PLB_lifejacket

Carrying a PLB, your chances of rescue in this situation increase dramatically. It is importnat to keep the antenna as upright as possible and make sure the internal GPS atenna has a clear veiw of the sky (image courtesy of McMurdo Group)


EPIRBs are an alternative and highly recommended means of alerting people to your distress at sea (and in the case of PLBs, over land as well). They have the advantage of offering truly global coverage and especially those with built-in GPS, highly accurate position information. Anybody who puts to sea should seriously consider carrying such a device, in addition to marine radio.

Note- thanks to McMurdo Group UK for the use of the images in this article

[1] As of December 2014, according to

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