MOB Devices

What this category covers and why it matters

Man-overboard (MOB) devices are safety tools designed to detect, mark and assist the recovery of a person who has fallen from a boat. The category includes personal locator beacons with integrated AIS (Personal AIS or AIS MOB), satellite and radio beacons with or without GPS, dedicated handheld VHF/DSC radios with MOB functionality, lifeline- or jackline-mounted MOB switches, wearable alarms that trigger onboard systems, throwable electronic markers and tethered retrieval aids such as rescue slings and heaving lines.

On any sailing boat, seconds matter after someone goes overboard. MOB devices reduce the time taken to locate the person in the water, allow for quicker alarm and rescue coordination, and in some cases automatically cue navigation and autopilot systems to assist the recovery. Which device or combination you need depends on where you sail, the size and crew of your boat, and whether you require automated signalling to remote vessels and shore services.

Where and how MOB equipment is used aboard a boat

MOB devices are used immediately after a crew member falls into the water. Typical actions include triggering an audible and visual alarm, marking the casualty’s GPS position, transmitting location to nearby vessels via AIS or VHF/DSC, and physically supporting or retrieving the person with a sling, ladder or ladder-basket. Some devices are designed for continuous monitoring (worn at all times), others are deployed only if an incident happens (throwable markers, grab bags).

Main product types and what’s excluded

• Personal AIS (AIS MOB) beacons: wearable units that broadcast the casualty’s position as an AIS target and may also sound alarms or send data to the vessel.
• Satellite personal locator beacons and PLBs: emergency beacons that transmit a distress message via satellite networks to search-and-rescue authorities; often a last-resort alert rather than a recovery aid.
• VHF/DSC radios with MOB function: handheld radios that can send an MMSI-coded DSC distress alert and mark the position on DSC-capable chartplotters.
• Deck-mounted MOB switches and lanyard kill switches: mechanical or electronic switches that cut engine power and can trigger alarms when a helmsman leaves the helm.
• Wearable alarms and inertial sensors: devices that detect water entry and raise an alarm automatically.
• Throwable locator devices and markers: electronic buoys or strobes that mark the casualty’s position without being worn beforehand.
• Tethered retrieval aids: rescue slings, lifebuoys, heaving lines and recovery ladders designed to bring a person back aboard.

Excluded are general-purpose emergency tools not designed specifically for MOB use (such as standard EPIRBs intended for vessel distress rather than individual recovery), generic lifejackets without integrated electronics, and routine deck hardware. MOB devices are a specialised subset of safety equipment focused on the immediate detection and recovery of an individual overboard.

Key terminology

• AIS (Automatic Identification System): a marine tracking system that broadcasts identity and position information to other AIS-equipped vessels and chartplotters.
• PLB (Personal Locator Beacon): a small emergency beacon carried by a person that transmits a distress signal to satellite search-and-rescue services.
• DSC (Digital Selective Calling): a VHF function that sends a digital distress alert to other DSC-equipped radios and search-and-rescue stations.
• MMSI: Maritime Mobile Service Identity, a unique number used for digital distress calls and device identification.

The decisions that matter before buying

Choosing an MOB device is about matching capability to risk. Consider these factors and why each matters aboard a sailing boat.

Boat size, type and intended use

• Smaller dayboats and trailer-sailers: a simple throwable marker and a reliable VHF may be adequate because recovery is usually nearby and help is close.
• Coastal cruisers: wearable AIS or VHF/DSC solutions that alert nearby traffic and chartplotters improve recovery chances in busy waters and at night.
• Offshore sailors: combination of wearable AIS, satellite PLB and well-practised retrieval procedures is typical because distance from help increases response time.

Crew size and experience

With a small crew, automated detection and clear, hands-free alarms reduce cognitive load during a crisis. Experienced crews may rely more on disciplined procedures and physical recovery gear, but electronic location aids still shorten search time.

Operating environment and conditions

• Cold water increases hypothermia risk and shortens survival time — faster locating is critical.
• High traffic areas benefit from AIS so other vessels can see and assist.
• Night or low visibility amplifies the advantage of electronic markers and strobes.

Power, integration and operation

Decide whether you need a self-contained wearable device or an integrated system tied to the boat’s electronics and power. Wearables are independent and continue to function if the boat’s power fails; integrated systems can trigger autopilot responses but depend on the vessel’s electrical systems.

Principal product types, how they work and when to use each

Wearable AIS MOB beacons

These units are worn on a lifejacket or harness and broadcast the person’s GPS position as an AIS target. They are most useful where other vessels or your own AIS-equipped boat can see and home in on the signal. Advantages include automatic location sharing and visual discrimination on chartplotters; limitations include limited transmission range in cluttered coastal waters and reliance on GPS fix speed.

Satellite PLBs and personal satellite communicators

PLBs send distress signals to national search-and-rescue agencies via satellite. Personal satellite communicators may additionally permit two-way messaging. Use these for offshore or remote sailing where shore-based rescue coordination is needed. They’re not a substitute for local locating aids during immediate recovery because rescue response time may be hours.

VHF/DSC handheld radios with MOB capability

Handhelds can send DSC distress alerts and, if GPS-enabled, transmit position data to DSC-capable chartplotters on your boat and others. They offer a familiar interface and are useful when crew are likely to have a radio at hand. They depend on VHF range and operator action unless combined with auto-trigger features.

Wearable inertial and water-activation alarms

These detect sudden movement, long falls or immersion and automatically trigger an alarm onboard and sometimes an external radio or AIS message. They reduce the need for manual activation but can suffer false alarms and may not always transmit if water or impact interrupts the device.

Deck-mounted switches, lanyards and helm kill systems

These are intended to stop propulsion and raise an alarm if the helmsman is displaced. They help prevent propeller-related injury and can help trigger immediate attention, but they do not locate the casualty in the water.

Throwable electronic markers and retrieval aids

Devices such as throwable lights and locator buoys can be deployed after the MOB event to mark the casualty’s position visually and electronically. Retrieval aids — slings, ladders and lifting bridle systems — assist in bringing someone back aboard. These are critical for immediate recovery, particularly in ship-assisted or singlehanded situations.

Understanding specifications and what they mean aboard

• Transmission type (AIS / VHF / Satellite): determines who will receive the signal and at what range. AIS targets are visible to AIS-equipped vessels and chartplotters; VHF/DSC reaches nearby boats and shore stations within radio range; satellite reaches rescue authorities anywhere but not necessarily nearby vessels.
• GPS accuracy and fix time: affects how precisely the casualty is marked. Faster fix times help in rough conditions; poor satellite reception can delay a coordinate broadcast.
• Battery life and replaceability: crucial for reliability — a worn or expired battery negates protection. Check whether batteries are user-replaceable while cruising.
• Water-activation and manual modes: water-activated devices reduce the need to press a button but can be triggered accidentally. Manual activation requires the wearer to act but avoids some false alarms.
• Mounting and wear options: how the device attaches to a lifejacket, harness or PFD affects likelihood it remains with the casualty and transmits correctly when in the water.

Compatibility and installation checks

• Physical mounting space for deck or helm switches and placement so a thrown device can be stored and reached quickly.
• Electrical and network integration: if you plan to connect a device to onboard AIS, DSC or NMEA networks, confirm voltage, connectors and whether special cabling or an interface is required.
• MMSI programming: DSC and AIS devices may need an MMSI code — ensure you have the correct MMSI and that it is programmed properly.
• Waterproofing and storage: devices must be accessible and protected from UV and salt when stowed, but ready for immediate use.
• Service access: confirm battery replacement procedure and whether replacement parts or service centres are available where you cruise.

Day sailing, coastal cruising and offshore considerations

Day sailing

Prioritise simplicity and fast deployment. A reliable VHF/DSC radio, throwable marker and a lifejacket with manual whistle and light are often sufficient. Focus on procedures and keeping devices in an accessible location.

Coastal cruising

Expect overnight sails and greater distances from immediate assistance. Wearable AIS or VHF/DSC devices that mark your position on chartplotters and alert nearby traffic are valuable. Keep throwables and retrieval aids ready for recovery in heavier seas.

Offshore and remote cruising

Offshore users should assume longer response times. Combine wearable AIS for local recovery with a satellite PLB for alerting rescue authorities. Redundancy, durable batteries and carry spares are essential. Practice recovery drills that rely as little as possible on external help.

Trade-offs to weigh

• Automation versus manual control: automated triggers reduce reaction time but can cause false alarms; manual controls require the casualty to act under stress.
• Wearable independence versus integrated systems: wearables work if the boat loses power; integrated solutions can provide more situational awareness but depend on the vessel’s systems.
• Weight and comfort versus likelihood of use: cumbersome devices may be left ashore; lightweight, comfortable equipment is more likely to be worn consistently.
• Immediate recovery aids versus long-range distress signalling: throwable markers and slings help recover the person now; satellite PLBs summon rescue services but are not a substitute for a quick local recovery capability.

Maintenance and service life

Regular checks keep MOB devices dependable. Inspect seals and housings for corrosion and UV damage, test batteries and replace according to manufacturer guidance, and verify GPS and transmitter function before extended trips. For devices integrated with vessel electronics, check connectors and network messages periodically. Carry spare batteries or a backup handheld radio when practical. Keep replacement parts or a plan for servicing in areas you cruise.

Common mistakes and how to avoid them

• Buying by headline features only: choose devices that suit your boat and routine; a feature-rich device is worthless if not worn or not installed correctly.
• Failing to consider installation limits: ensure integration needs, cabling and space are feasible before purchase.
• Underestimating human factors: overly complex gear that is difficult to operate under stress will be less effective; favour intuitive controls and clear alarms.
• Neglecting battery replacement and testing: an expired battery renders a device useless; include checks in pre-departure routines.
• Assuming one device covers all risks: combine local locating aids with long-range distress signalling when sailing offshore rather than relying on a single solution.

Before you buy — practical checklist

• Intended use: day sailing, coastal cruising or offshore? Match device capability to that environment.
• Boat information: available mounting locations, 12/24 V power availability, existing AIS/DSC capability and network connections.
• Crew habits: will people consistently wear a device? Choose comfortable, unobtrusive wearables if necessary.
• Integration needs: do you require autopilot or chartplotter alerts? Confirm compatibility and cabling requirements.
• Battery and servicing: can you replace batteries while cruising? Are spare parts and service points available on your route?
• Training and drills: plan how you will practise cancelling an MOB, deploying throwables and recovering a person with the chosen gear.
• Questions for supplier/installer: power draw, waterproof rating, expected life of batteries, programming of MMSI and how the device interacts with onboard alarms.

Prioritise solutions that you and your crew will use consistently and that are compatible with your boat’s systems. In many cases a layered approach — wearable AIS for quick local location, a VHF/DSC radio for immediate communication, and a satellite PLB as a backup for remote trips — gives balanced protection without excessive complexity. Ultimately, equipment reduces time to locate and recover a person, but well-rehearsed procedures, proper clothing and seamanship remain central to successful MOB recovery.