A signal pistol or even rockets may have been effective in the days of the Titanic, writes circumnavigator and author Bobby Schenk in our news from June 16, 2024, but today they can be replaced much more effectively by powerful LED headlights or various radio signals. The most effective and widespread nowadays are distress radio signals from EPIRBS – Emergency Position-Indicating Radio Beacon Stations. But how do these radio beacons, which every long-distance sailor should have on board, actually work?
An emergency position-indicating radio beacon (or EPIRB for short) is a radio transmitter that every long-distance sailor should have on board today as part of their basic emergency safety equipment. The devices, which are also called “emergency position-indicating radio beacons” (or, for short, EPIRBs), are, to put it simply, nothing more than a radio station for the mobile phone service, the transmissions of which are designed to facilitate the search and rescue work of boats at sea (see also our article “life-saving equipment on board“).
As a rule, small radio transmitters are used with EPIRBs, for example as a radio station for rescue equipment, with the help of which satellites or search and rescue forces can locate not only people or aircraft in need of rescue, but also ships – or pleasure craft, which is the sole subject of this article. But how do these practical devices, which are now available in very compact designs, actually work?
An EPIRB can be triggered automatically – by contact with water – or manually.
An emergency radio beacon is activated either manually or automatically. Generally speaking, EPIRBs are designed to be activated by contact with water. Once triggered, the beacon transmits an alert signal on one or more standardized emergency frequencies, which for newer always on 406 MHz. To trigger it manually, a fuse must first be removed and a button pressed to prevent accidental triggering.
Automatic-transmit EPIRBs may also have a submersible pressure-housing. When a vessel sinks, the beacon is ejected from the housing, rises to the surface and begins transmitting the distress signal. To function properly, it must be able to float freely. Nevertheless, this device should also be operable manually (in case of an emergency on board, for example, a fire on board or a pirate attack).
The distress signal is received by satellites of the COSPAS/SARSAT system and forwarded to a (usually unmanned) ground station (local user terminal, LUT). From there, it is forwarded to a rescue coordination center (RCC), such as the Bremen Sea Rescue Coordination Center of the DGzRS in Germany or the US Coast Guard in the USA (YouTube US Coast Guard Training). The Coast Guard evaluates the signal and immediately initiates search and rescue measures.
Modern EPIRBs receive satellite signals and are part of the GMDS system
Modern emergency radio beacons are designed to be received by satellites and (in shipping) are part of the Global Maritime Distress and Safety System (GMDSS). In addition to the alarm signal, they usually also transmit a bearing signal on 121.5 MHz, which enables SAR aircraft or ships to home in on the emergency position (also known as homing).
Note: older emergency locator beacons transmit exclusively on 121.5 MHz and are designed for reception by passing aircraft. They are not part of the GMDSS and are no longer recommended today. In addition, there are emergency locator beacons for the immediate coastal area that transmit an emergency signal directly to the nearest coastal radio station via VHF.
Emergency beacons are usually brightly colored, no larger than 30 cm, freely available on the market, and cost several hundred to several thousand euros, depending on the design and application. High-quality beacons are distinguished, among other things, by an integrated GNSS receiver. GNSS stands for Global Navigation Satellite System, a collective term for the use of existing and future global satellite systems for positioning and navigation.
For EPIRBs, batteries must be replaced regularly, if necessary by a specialist
company, even while at sea.
This GNSS receiver makes it possible to send not only information such as the identity of the transmitter and the type of emergency, but also one’s own position in the emergency signal, which can significantly reduce the time needed for search and rescue. The lifespan of a (modern) emergency radio beacon is about ten years. The manufacturer’s instructions for maintenance should be observed (these usually refer to battery replacement). For newer EPIRBs, batteries should last at least five years.
Satellite-based emergency beacons are mandatory for seagoing vessels in international voyages of 300 GT and above and for all passenger ships under the SOLAS treaty for seagoing vessels in international voyages of 300 GT and above, as well as for all passenger ships. In contrast, their use in recreational boating is voluntary and – partly due to their high price – not very common in coastal areas.
The basis for the functioning of the EPIRBs is the COSPAS/SARSAT system, developed in the 1980s. Today, it includes six low-Earth orbiting search and rescue (LEOSAR) weather satellites that monitor the internationally agreed distress frequency 406 MHz. Signals received on this frequency are stored and forwarded to a ground station as soon as possible.
Signals are detected in a matter of seconds or hours, depending on their location.
The beacon is detected by one of the satellites after no more than four hours. If the transmitting emergency radio beacon can determine its own position using an integrated GNSS receiver, this information is sent along with the distress signal, enabling highly accurate (100 m) localization. Emergency beacons for 406 MHz transmit an identity signal with the distress signal, so that many false alarms can be clarified by queries before a rescue operation is initiated.
In addition to the polar-orbiting satellites, the COSPAS/SARSAT system has also had geostationary satellites (geostationary search and rescue, GEOSAR), which also receive signals at 406 MHz. The advantage of this system is that geostationary satellites are constantly “watching” large parts of the earth’s surface and can therefore receive distress signals sent between approximately 70° north and south latitude within a few seconds and forward them to one of the designated ground stations.
Many of the satellites in the global navigation satellite systems (GNSS) GPS, GLONASS and GALILEO are equipped with a MEOSAR (Medium-Earth Orbit Search-and-Rescue) additional module for receiving distress signals (406 MHz) and forwarding the distress signals to the corresponding ground stations (MEOLUT).
The most common type of EPIRB transmits on 406.025 and 406.028 MHz and is received by the COSPAS/SARSAT system.
There are currently several types of emergency radio beacons available on the market, which differ in the alerting system used and the range of accessories. A common type of emergency radio beacon, which is also part of the GMDSS, transmits on 406 MHz (more precisely: 406.025 MHz and 406.028 MHz). Its signal can be received and forwarded by all COSPAS/SARSAT system satellites.
Most of these beacons also emit a weak signal at 121.5 MHz as a homing signal. 406 MHz emergency beacons are divided into two categories: Category I devices can be triggered automatically or manually, while Category II devices can only be triggered manually. In addition, emergency beacons can be equipped with search and rescue radar transponders (SART) that responds to 9 GHz radar signals.
COSPAS/SARSAT beacons are registered with a specific vessel when purchased. When activated, the personal locator beacon transmits a personal identification feature, such as its serial number or the ship’s Maritime Mobile Service Identity (MMSI) (a globally unique ship’s call number in the GMDSS), as well as its position, if a GNSS receiver is integrated.
The contact details provided help to clarify false alarms before rescue operations
The registration process ensures that the emergency signal provides the rescue coordination center with important information, such as the type of vessel involved (e.g. yacht or tanker). Contact details provided at the time of purchase, for example of relatives, also enable the control center to clarify many false alarms before a rescue operation is initiated. It should be noted that the contact provided should not be on the ship, but on land, and should be familiar with the trip planning (when / where / who is on board?).
Incidentally, modern maritime EPIRBs transmit two distress signals simultaneously: in addition to the distress signal via the COSPAS/SARSAT satellite network, it is also an emergency signal sent via the AIS. The emergency signal sent via AIS is received by nearby ships.
All ships equipped with an appropriate AIS receiver (mandatory for SOLAS-regulated ships, but increasingly common on larger leisure craft as well) can pick up the AIS radio signal and immediately see the position of the stricken vessel on their chart plotter.
AIS-EPIRBs must be equipped with a GNSS receiver. Advantage: the transmission via AIS of the current position of ships, lifeboats or persons in distress at sea can speed up the rescue operation.
For coastal areas, there are emergency beacons that alert via DSC on VHF channel 70.
For the immediate coastal area, emergency beacons are available that transmit an emergency alarm via Digital Selective Calling (DSC) on VHF channel 70. Their major disadvantage is the limited range of a maximum of 30 nautical miles to the nearest coastal radio station. A VHF marine radio offers the same function, with the added advantage that after the alert, contact can also be established with a coastal station or other ships via VHF radio.
A VHF DSC EPIRB only offers added value if it is also equipped with an integrated radar transponder to help SAR personnel locate it. A VHF DSC EPIRB may only be used on ships that only sail in sea area A1 (division of the world’s oceans into four sea areas by the IMO, International Maritime Organization).
Sea area A1 is the area within the radio range of at least one VHF coast radio station that is continuously available for DSC alerts (channel 70/156.525 MHz). Typically, the area extends 30–40 nm (56–74 km) from the coast.
EPIRBs must be registered with the telecommunications authority and coded with an individual MMSI at a charge.
For German yachts, the following applies: the EPIRB must be registered with the Bundesnetzagentur (subject to a fee). The device is then entered in the so-called frequency allocation certificate for the ship.
Austrian citizens: must register their devices with the Austrian telecommunications authority.
Each EPIRB is coded with a MMSI (Maritime Mobile Service Identity) when registered, a unique number that is assigned to a corresponding marine radio station.
By the way: whether an EPIRB is mandatory for a particular area of travel or not is determined by the law of the flag state. If the flag state does not specify this, the law of the country in which the yacht is traveling applies. However, if in doubt, a radio beacon to indicate the position in an emergency should always be on board when traveling on the open sea.
And: the EPIRB should be part of the boat briefing before the start of the trip, because the device is not a toy – even an accidental activation inevitably triggers the entire rescue chain. Everyone on board should therefore know the importance of the radio beacon, the basics of how it works and the different ways of triggering it.
This includes knowing, for example, that a beacon triggered by contact with water must be reactivated manually when it is taken out of the water, for example because the crew is in a lifeboat and the buoy has been taken into the lifeboat. In addition, in the event of an unintentional activation, not only must the EPIRB be switched off immediately, but it is also imperative to inform the responsible Rescue Center immediately that it is not an emergency.