Man Overboard: Is It Best to Have An AIS, a PLB, or Both?

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Man overboard situations are stressful for all involved, even in calm waters. Rarely does it happen in an ideal situation, and in challenging conditions in foul weather, it is a race against time to find the person in the water before they disappear from sight entirely. Those first 60 seconds after falling overboard are critical. 

 

That’s why man overboard technology has been developed though; to help make recovering the person simpler. There are two main types of man overboard beacon: AIS and PLB. In this post, we’re breaking down the difference between the devices, to help make it clear which one best suits your needs. 

AIS MOB: The Local Lifeline

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What it stands for: Automatic Identification System (Man Overboard)

Best for: Coastal cruising, racing with a crew, daytime sailing

Examples: Ocean Signal RescueME MOB2, ACR AISLink

The easiest way to think of an AIS MOB device is as a localised distress flare, but one that is picked up by computer screens. As soon as the device is triggered, it begins broadcasting an emergency signal via VHF radio frequencies.

 

Instead of alerting a distant Coast Guard station, it directly alerts the vessels closest to you. Within seconds, your signal overrides the chartplotters, radar screens, and AIS receivers of every modern boat within a 4 to 5-mile radius. Crews won’t just hear an alarm; they will look at their screen and see a flashing red "MAN OVERBOARD" icon pinpointing your exact GPS coordinates, heading, and distance. 

 

Because the device continuously updates your position, it accounts for tidal drift, allowing your crew (and other local vessels) to turn the boat around and track you down with absolute precision.

PLB & EPIRB: The Global Safety Net

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What it stands for: Personal Locator Beacon | Emergency Position Indicating Radio Beacon 

Best for: Solo sailors, remote offshore passage-makers, and ocean-crossing delivery skippers.

Examples: Ocean Signal RescueME EPIRB1, ACR GlobalFix V4 

While an AIS device shouts to the immediate neighbourhood, a PLB or EPIRB summons a global response. If you fall overboard and your vessel continues sailing away on autopilot, or if your boat sinks rapidly beneath you, local VHF frequencies won't cut it. You need a signal that can go beyond the horizon.

 

The moment a PLB or EPIRB is activated, it broadcasts a powerful 406 MHz emergency signal directly to the international Cospas-Sarsat satellite network. This signal ignores nearby boat traffic and routes instantly to a dedicated land-based receiving station, which identifies your specific beacon registration and alerts the nearest international search and rescue (SAR) authority, like the Coast Guard. 

 

These units also use an internal 66-channel GPS to embed your exact coordinates into the satellite message, alongside a secondary 121.5 MHz homing signal. This dual-frequency layout acts like a breadcrumb trail: the satellites get the rescue helicopters or cutters to your general area, and the homing signal allows them to pinpoint your exact spot in the swell, even in zero visibility. 

PLB vs. EPIRB: What’s the Difference?

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While both devices use the same satellite network to alert the Coast Guard, they serve completely different roles:

 

An EPIRB belongs to the boat. It is registered to the vessel's name and MMSI. Larger heavy-duty units are mounted in brackets on deck or in a grab bag. They are designed to float upright on their own and will transmit an SOS for at least 48 hours. Choose an EPIRB if you are outfitting a vessel for offshore cruising, short-handed night passages, or ocean crossings.

 

A PLB belongs to the person. It is a pocket-sized unit registered to an individual, meaning you can carry it with you from boat to boat. They are designed for personal survival, and must be manually activated to transmit for a minimum of 24 hours. A PLB is the perfect choice for solo sailors, delivery skippers, or crew members who want personal man-overboard protection tucked safely inside their TeamO BackTow lifejacket.

 

For serious offshore sailing, the best setup is a vessel-registered EPIRB mounted near the companionway for the boat itself, and personal PLBs or integrated AIS devices packed into the crew's lifejackets.

What Regulations Matter When Choosing an AIS or PLB?

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When buying safety electronics, you aren't just dealing with battery life and ranges; you also need to navigate international and domestic maritime laws. Falling foul of these rules doesn't just mean a less effective rescue; it can land you with a heavy fine and even prison time.

 

The 2026 PLB Registration Law (UK)

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For over two decades, it has been a legal requirement to register full-sized EPIRBs on the national database. However, personal PLBs occupied a legal grey area – until now. Under the Merchant Shipping (EPIRB and PLB Registration and Radiocommunications) (Amendment) Regulations 2026, it is now legally compulsory to register all 406 MHz PLBs carried on board any UK-flagged vessel, hovercraft, or mechanically propelled watercraft. 

 

Who is responsible? The legal responsibility falls squarely on the individual who owns the PLB. If a crew member brings their own beacon aboard clipped to their lifejacket, they are responsible for its registration. 

 

How do you do it? Registration is completely free and takes about 15 minutes via the UK 406 MHz Beacon Registry (MCA) online. You will need your device’s unique 15-character Hexadecimal ID (printed on the unit), your emergency contacts, and your primary vessel details. 

 

Why it matters: If you activate an unregistered beacon, search and rescue teams will still launch, but they will be flying blind. They won't know if they are looking for a solo sailor on a 30ft yacht or a family on a coastal cruiser, costing precious time. Failing to register your device can now result in steep fines or a prison term up to two years, although at the time of writing no convictions have been made, so there's no legal precedent set. 

 

Crucial buying tip: If you buy an ACR or Ocean Signal unit second-hand or from an overseas retailer, ensure it is coded for the UK (country codes 232, 233, 234, or 235). The UK Beacon Registry cannot register a device coded to another country unless it is officially reprogrammed by a manufacturer. 

 

AIS Licensing and MMSI Numbers (UK)

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Unlike satellite-based PLBs, an AIS MOB device operates over VHF marine radio frequencies. Because it acts as a tiny radio transmitter, an AIS device must be legally tied to a vessel’s MMSI (Maritime Mobile Service Identity) number or be pre-programmed with a specific, manufacturer-assigned maritime identification number that identifies it explicitly as an MOB unit.

 

For the Boat: Your vessel must hold a valid Ship Radio License (issued by Ofcom in the UK) to legally operate AIS equipment.

 

For the Device: Each AIS comes with its own unique 9-digit maritime identity that instantly tells any passing ship's chartplotter that the signal coming across the airwaves is a live person in the water, not an oncoming boat, ensuring it triggers an emergency alarm on their bridge.

 

Global Regulations

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If you are a sailor based in the US, Australia, or Europe, the rules are just as strict. Registration of 406 MHz PLBs and EPIRBs is legally mandatory under bodies like NOAA in the US and AMSA in Australia. No matter where you live, registration is always free, and your beacon must be programmed with the country code matching the flag of your vessel or your home nation. 

 

United States (NOAA)

The Law: Registration of all 406 MHz PLBs and EPIRBs is strictly mandatory under federal law (FCC and US Coast Guard regulations).

The Registry: Free via the NOAA SARSAT Beacon Registration database.

Be Aware: Coordinated explicitly to the USA country code. Like the UK, NOAA will not register a beacon programmed with a foreign country code. It must be updated every two years.

Australia (AMSA) & New Zealand (Maritime NZ)

The Law: Registration is mandatory. Australia has some of the strictest enforcement rules in the world due to the vastness of their search and rescue zones. 

The Registry: Free via the Australian Maritime Safety Authority (AMSA) or the Beacons New Zealand registry.

Be Aware: Fines for carrying an unregistered beacon are heavy. Australia does not allow the sale or use of 406 MHz beacons without a built-in GPS.

Europe & The Rest of the World

The Law: Varies slightly by country, but under international Cospas-Sarsat agreements, almost all European countries require mandatory registration.

The Registry: If a country doesn't have its own dedicated national beacon registry, sailors must register their device with the International Beacon Registration Database (IBRD).

Keeping Your MOB Device Ready

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Investing in a premium lifejacket and beacon is step one, but they only work if they’re on your person when you go overboard, and if they function flawlessly in a worst-case scenario.

How long do the batteries last in an AIS or PLB?

Most modern personal beacons from premium brands like Ocean Signal and ACR feature a storage life of 5 to 7 years. This doesn't mean the battery dies in 7 years; it means the specialised lithium-metal cells are guaranteed to retain enough capacity to meet their full legal transmission time (24 hours for a PLB/AIS, 48 hours for an EPIRB) up until that printed expiry date. 

Can I change the battery myself?

No. Unlike a flashlight or your TV remote, you cannot simply swap out the batteries at home. These are hermetically sealed, lifesaving medical/survival devices. Opening the case yourself will instantly invalidate the manufacturer's warranty and compromise watertight seals. 

 

When your unit reaches its expiry date, it must be sent to an authorised service agent. Technicians will completely replace the internal battery pack, renew the rubber O-rings and gaskets, and run the device through specialised diagnostic machinery to test signal strength and water-resistance before recertifying it. 

Do MOB devices require routine servicing?

Aside from battery replacement at the 5-to-7-year mark, they do not require formal annual servicing, but they do require basic owner maintenance:

 

The Monthly Self-Test: Every AIS and PLB features a dedicated test button. Pressing this executes an internal diagnostic check on the circuitry, battery health, and strobe light. Doing this once a month (especially before a major passage) ensures everything is live.

 

The Annual Lifejacket Inspection: If your AIS is integrated into your TeamO BackTow lifejacket, it should be visually inspected during your annual lifejacket service. Ensure the automatic firing tab is still seated correctly, the antenna isn't kinked, and there is no corrosion around the activation switches.

What happens if I accidentally set off my beacon?

Accidental activations happen, often when installing a device into a lifejacket. If your beacon starts flashing or sounding an alarm:

 

Turn it off immediately using the manual override button.

 

Do not hide it. If it is a PLB or EPIRB, the satellite signal may have already reached the Coast Guard. Call the closest maritime rescue coordination center as soon as possible to report a false alarm so they can stand down emergency assets. There are likely to be no penalties for an honest accident, but failing to report it wastes critical rescue resources.

Don't Leave Safety to Chance

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So, is it best to have an AIS, a PLB, or both? Your choice depends on how and where you’re going. If you primarily sail with a trusted crew along the coast, an AIS MOB is likely to be your fastest ticket back on board. If you often sail solo or make long offshore passages, a PLB ensures international rescue services are alerted. But for total peace of mind on open water, pairing both tracking methods, or upgrading to a modern, all-in-one combined beacon, means you’re covered for every eventuality.

 

And of course, before you head out on your next passage, make sure your safety array is fully updated, registered, and integrated, so you can focus on the adventure ahead of you. 

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