DataHub Pro Man Overboard, AIS MOB beacons and 406 MHz Personal Locator Beacons (PLBs) can all help in a man overboard emergency, but they work in different ways and are designed to solve different parts of the MOB problem.
The main differences are how an MOB is detected, who is alerted, how the person is located, and how help is summoned. Understanding those differences can help you decide what combination of equipment and procedures is appropriate for your boat and crew.
| DataHub Pro Man Overboard | AIS MOB beacon | 406 MHz PLB |
Primary purpose | Detect separation and rapidly alert your own crew | Broadcast the MOB's position to your boat and nearby equipped vessels | Alert Search & Rescue authorities |
What the person carries | Supported phone or watch | Dedicated beacon, commonly fitted to a lifejacket | Dedicated personal distress beacon |
Can activate automatically? | Yes. While monitoring is active, loss of the connection between the device and DataHub Pro can trigger the MOB workflow. | Yes on compatible models/installations, commonly when an inflatable lifejacket deploys. | Generally manual. |
Alerts your own crew | Yes. Alerts are sent to monitored phones/watches aboard. | Yes, when received by compatible AIS/DSC equipment aboard. | Not normally directly. |
Audible warning aboard | Yes. A key part of the DataHub Pro workflow. | Typically yes when supported by the receiving AIS/MFD/DSC equipment. | Not inherently. |
MOB shown on chartplotter | Yes, when DataHub Pro is correctly connected and configured with a compatible NMEA 2000 chartplotter. | Yes, on compatible AIS equipment as an AIS MOB target. | Not with a conventional 406 MHz PLB. |
MOB position source | DataHub Pro generates the MOB information using the position available to the system at activation. | GNSS/GPS built into the beacon tracks the person in the water. | GNSS/GPS-equipped PLBs transmit their position through the 406 MHz distress system. |
Alerts nearby boats | Not directly. | Yes. AIS transmissions can be received by vessels within radio range; some devices also support DSC. | Not directly. |
Alerts shore contacts | Yes. Email and SMS can be sent when Internet and required services remain available. | Not normally. | Alerts are handled through the international Search & Rescue system rather than personal email/SMS contacts. |
Alerts a Rescue Coordination Centre | Not inherently a 406 MHz distress alert. | Not inherently. | Yes. This is the PLB's key role. |
Communication dependency | Local connection between monitored devices and DataHub Pro. Internet is additionally required for services such as email/SMS. | VHF/AIS radio range between the beacon and receiving vessels. | 406 MHz Cospas-Sarsat satellite system. |
Typical response | Your crew is alerted and can begin the MOB response. | Your boat and potentially nearby vessels can locate and respond to the MOB. | Search & Rescue authorities coordinate a response. |
Key strength | Crew awareness and automatic separation detection, including crew carrying a monitored phone/watch. | Broadcasting the casualty's own position locally to equipped vessels. | Direct access to the international Search & Rescue system. |
Key trade-off | Depends on DataHub Pro, monitoring, power, local connectivity and correct configuration. | Depends on the person carrying the beacon and its signal being received within radio range. | Normally requires the person to activate it and does not inherently alert their own boat immediately. |
Where DataHub Pro Man Overboard fits
DataHub Pro Man Overboard is designed around an important first problem in an MOB emergency: does the crew aboard know that someone has become separated from the boat?
Each monitored phone or watch maintains a continuous connection with DataHub Pro. Both the device and DataHub Pro monitor that connection.
With the current beta behaviour:
The disconnected device alerts immediately.
After approximately 10 seconds, other monitored devices still connected to DataHub Pro alert.
After approximately 30 seconds, the MOB event activates.
Beta timing: Exact alert and activation timings may change while Man Overboard is under development.
When the required dependencies remain available, DataHub Pro can also send MOB information onto NMEA 2000 for a compatible chartplotter, and email and SMS notifications can be sent.
This means a crew member doesn't need to manually press a distress button for DataHub Pro to detect that their monitored device has disappeared from the boat's network. A phone or watch may also be carried throughout normal life aboard, providing monitoring whenever the device is supported, connected and monitoring is active.
Where an AIS MOB beacon fits
An AIS MOB beacon travels with the person in the water. Compatible models contain their own GNSS receiver and transmit the casualty's position over AIS. Your yacht's compatible AIS/MFD equipment can then show the MOB position, while other suitably equipped vessels within radio range may also receive the transmission.
Some AIS MOB devices can be installed inside an inflatable lifejacket so the beacon activates when the lifejacket inflates.
Its major strength is therefore different from DataHub Pro Man Overboard: the beacon can transmit the casualty's own position from the water.
AIS MOB range depends on VHF radio propagation, antenna height, sea conditions and receiving equipment, so a fixed range should not be assumed.
Where a 406 MHz PLB fits
A PLB is primarily designed to call Search & Rescue. When activated, a 406 MHz PLB sends a distress signal through the Cospas-Sarsat satellite system. That alert is passed through the international Search & Rescue network to the appropriate Rescue Coordination Centre, which can coordinate a rescue. A GNSS-equipped PLB can include the person's position in that distress information.
This makes a PLB particularly valuable when assistance is required beyond the person's own vessel or nearby vessels.
The trade-off is that conventional PLBs are generally manually activated. They also do not inherently make the casualty appear as an MOB target on the yacht's chartplotter or immediately alarm every crew member aboard.
What about devices that combine AIS and 406 MHz?
Some modern personal beacons combine AIS local alerting and 406 MHz satellite distress alerting in one device. These can broadcast the casualty's position to suitably equipped nearby vessels while also transmitting a 406 MHz distress alert through the Cospas-Sarsat system.
Check the specifications, activation method and lifejacket compatibility of the particular beacon you are considering.
What about range?
The three systems shouldn't be compared using one simple range figure because they communicate in fundamentally different ways.
DataHub Pro Man Overboard detects the loss of connectivity between the monitored device and DataHub Pro. Moving beyond the boat's DataHub Pro connectivity can therefore become the event that triggers separation detection. Its purpose isn't to maintain a long-range radio link to a person in the water.
AIS MOB broadcasts from the casualty over VHF/AIS. Its useful range depends on radio conditions, antenna height and receiving equipment.
PLB uses the international 406 MHz satellite distress system and is intended to alert Search & Rescue beyond local vessel radio range.
Which should I choose?
A useful way to think about the technologies is to consider the problem you want each one to solve.
"I want everyone aboard to know quickly that a crew member has become separated from the boat."
DataHub Pro Man Overboard is designed around crew awareness and automatic separation detection.
"I want the person in the water to transmit their own position to my boat and nearby vessels."
An AIS MOB beacon is designed around local position transmission.
"I want the person in distress to be able to summon Search & Rescue through the international satellite distress system."
A registered 406 MHz PLB is designed for this.
These capabilities can overlap, particularly with newer combined beacons. A skipper may choose one or several technologies according to the vessel, type of sailing, crew, watchkeeping arrangements and risks they want to manage.
MOB safety is more than the alert
Whichever MOB technology you choose, it works best as part of a complete onboard MOB plan. Four things are worth considering.
Prevention — don't go overboard
The best MOB outcome is preventing it from happening. Continue to use appropriate lifejackets, harnesses, tethers, jackstays and safe onboard procedures for your vessel and conditions.
Findability — make the person easier to locate
A person in the water can be extremely difficult to see, particularly at night or in waves. AIS MOB devices can provide an electronic position, while appropriate lifejacket lights, strobes and whistles can also help the crew locate the casualty.
Recovery — have a plan to get them back aboard
Finding the person is only part of the problem. Consider how your crew would manoeuvre back to them and physically recover an injured, exhausted or unconscious person onto your particular boat.
Testing — make sure it actually works
Test your equipment and practise MOB drills before you need them. With DataHub Pro Man Overboard, confirm that crew devices alarm and that your expected chartplotter, email and SMS alerts work. Test other MOB devices according to their manufacturers' instructions.
For shorthanded crews, make the test realistic: will the MOB alarm actually wake the off-watch crew member below?