PLB and AIS-MOB system (personal distress beacons)

PLB and AIS-MOB system (personal distress beacons)

Marine distress beacons, also known as emergency radio beacons or MOB systems, are now an integral part of the equipment of many yachts. This is not without reason, as development has advanced significantly in recent years. In particular, the integration of modern transmission technology has significantly improved the location of a yacht in distress or a crew member who has fallen overboard.

Today, there are distress beacons that can alert rescue services from anywhere in the world and share their location. This represents a huge safety benefit for cruising and blue-water sailors. The most modern distress beacons even display confirmation that the distress call has been received, certainly a reassuring feature for all those involved in an emergency situation. This process is called the Return Link Service (RLS).

Sailors have access to highly efficient technologies, such as the Global Positioning System (GPS). GPS technology is highly accurate and limits the potential search radius to just a few meters. In addition to the GPS signal, state-of-the-art radio technology is also used. These include the Automatic Identification System ( AIS ) and satellite-based systems such as the Emergency Position Indicating Radio Beacon ( EPIRB ).

All of these systems have long been standard safety features on seagoing yachts. Systems that are primarily tied to a vessel are deliberately not the subject of this article. Instead, it will describe the use of these technologies in personal rescue systems, known as PLB or AIS-MOB systems.

Properties of personal distress beacons

Increasingly compact technology has made it possible to build marine distress beacons with GPS, AIS, and EPIRB technology so small that they can be worn directly on the body. This makes them part of personal safety equipment, not part of the yacht's equipment. Consequently, a separate system must be planned for each crew member.

If a person falls overboard, the emergency radio beacon is activated either manually or automatically and transmits a distress signal with the position. Depending on the system, the GPS position is transmitted either as an AIS signal to vessels within range or, as with an EPIRB, via satellite to the responsible rescue coordination centers, which then initiate the search. This not only significantly simplifies the location of a person drifting at sea, but in the best case scenario, maritime rescue teams are also on site.

Differences in the transmission technology of personal distress beacons

Emergency beacon with satellite-based transmission technology (EPIRB/SPOT)

Personal locator beacons (PLBs) that function like EPIRBs are called personal locator beacons (MMSIs). Like an EPIRB, a PLB transmits the MMSI number and GPS position via COSPAS-SARSAT satellites to responsible ground stations such as the Mission Control Center or Bremen Rescue, which then organize and coordinate assistance.

In Germany, the personal registration of distress beacons is not permitted. Therefore, the PLB must instead be programmed like an EPIRB, which always refers to a yacht and not a person, with an MMSI number previously applied for with the Federal Network Agency.

Those who still want to use the PLB for personal use rather than for a specific ship can alternatively register it abroad. Some manufacturers, for example, offer to register the PLB in England.

Sailors who travel exclusively on their own yachts can opt for vessel-specific registration using an MMSI number through the Federal Network Agency. Charter sailors or transfer skippers who regularly sail on other yachts should opt for personal registration abroad.

Depending on the satellites' position in the sky, reception of the distress signal via the COSPAS-SARSAT system can take up to 45 minutes. This can be faster if the distress beacon operates not only with COSPAS-SARSAT but also with satellites of the MEOSAR system. MEOSAR includes over 70 additional satellites, providing additional coverage and, consequently, faster activation.

The emergency signal is transmitted on the emergency frequency of 406 megahertz, while the emergency call is simultaneously transmitted on the emergency frequency of 121.5 megahertz used by aircraft and rescue cruisers.

Caution: Once triggered, a PLB initiates the rescue chain. This is important to know if it was triggered accidentally! If the alarm is triggered accidentally, or if a person has been rescued without external assistance, the emergency call must be canceled via radio or other means of communication. Simply turning off or deactivating the distress beacon does not cancel the emergency call. This does not apply to any test function that may be present in the distress beacon. This does not trigger an emergency call.

Various satellite trackers offer an alternative to a personal emergency beacon using satellite technology. Satellite trackers are particularly popular with mountaineers, pilots, and outdoor sports enthusiasts and are also used on board some cruising yachts. In addition to tracking, some of these systems also have an SOS button that sends an emergency call via the satellite system. With these devices, the emergency call is not sent directly to the responsible maritime rescue coordination center, but rather to the GEOS International Emergency Response Coordination Center (IERCC), which then contacts the rescuer via the tracker's messenger function and organizes assistance if necessary.

Marine distress beacon with radio-based transmission technology (AIS)

A personal distress beacon with AIS technology is called an AIS-MOB. MOB stands for "Man Over Board." If a crew member falls overboard, the AIS-MOB transmits an AIS signal that is displayed by all AIS receivers within range. The distress signal can be received by both Class A and Class B transponders . As is common with AIS, the signal is transmitted via VHF radio, so the range is limited to the antenna height of the transmitter and receiver. The range of AIS-MOB distress beacons is generally limited to 20 nautical miles.

Some AIS-MOB marine distress beacons can also be programmed with an MMSI number. When triggered, a DSC alarm is triggered on the radio with the corresponding MMSI number. This immediately alerts the crew if someone has fallen overboard. Unfortunately, a general DSC broadcast distress call is not possible with an AIS-MOB.

Which distress beacon technology is right for whom? PLB versus AIS-MOB

AIS-MOB emergency radio transmitters are not only somewhat cheaper, but unlike a PLB, they also don't require complex programming and registration with the Federal Network Agency. However, AIS-MOB transmitters have two disadvantages that can be crucial in an emergency.

The range is limited to the VHF marine radio range, which means that triggering the alarm doesn't necessarily guarantee professional assistance/rescue, as I'm heavily dependent on who is nearby. Furthermore, anyone receiving an AIS MOB signal should, as a precaution, mobilize additional rescue personnel in addition to their own.

But even if a PLB is triggered, there's no guarantee that only professional rescuers will arrive. The rescue coordination center can see exactly which vessels can help most quickly and contact them specifically to set a course for the alarm position. For example, a container ship might deviate from its course to assist, forcing the helicopter to stay on land for the time being.

It is interesting to note that when a PLB is triggered, details can be clarified via stored emergency numbers, such as possible pre-existing medical conditions or the age of the person in distress.

In busy coastal areas, an AIS-MOB distress beacon may be sufficient, as there is usually a vessel with a suitable AIS receiver within range that can receive the distress signal. In more remote areas, the only option for rescue is the crew sailing on board their own yacht. Therefore, an AIS-MOB is not helpful for single-handed sailors!

Nevertheless, a key advantage of an AIS-MOB distress beacon is that the signal can be received on the on-board AIS; the signal from a PLB cannot be received on private yachts.

Anyone sailing solo, planning night trips , or offshore where relatively high seas make locating a person overboard even more difficult is better advised to have a PLB. This allows for quick and professional assistance in the event of a maritime emergency.

What should I consider when buying?

Marine distress beacons are used in emergency situations, meaning they must function even under extreme conditions at sea. They must be waterproof, ideally also shockproof and buoyant. Protection against accidental activation should also be in place, as an alarm triggered without an emergency can have annoying and often costly consequences.

The activation method of the distress beacon is adjustable on high-quality AIS MOBs. For example, it can be helpful if a distress beacon is automatically triggered if the person wearing it falls into the water. This is particularly advantageous in regions with cold water, which can quickly cause the victim to faint. Many emergency beacons also have an integrated flashlight, which further assists in locating a person who has fallen overboard in the dark.

Rescues don't always happen quickly and smoothly. Therefore, marine rescue transmitters must have powerful batteries that guarantee at least 24 hours of continuous transmission power.

Conclusion

Falling overboard on the high seas is one of the worst nightmares for blue-water and cruising sailors. A crew member who falls overboard in rough seas, and then unnoticed, is usually hopelessly at the mercy of their fate. Even near the coast, finding a person floating in the water at night or in poor visibility can be difficult. With a personal distress beacon, modern tracking technology is worn directly on the body, greatly increasing the chances of being found in time. An unbeatable safety benefit for sailors!

Soon, the first combined devices will be available that combine AIS-MOB and PLB, yet are small enough to be worn on a life jacket. They will then be able to connect four emergency frequencies simultaneously: the global distress signal at 406 MHz, the bearing frequency at 121.5 MHz, precise GPS positioning, and local tracking via AIS.