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 differently and address 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 these differences can help you decide which combination of equipment and procedures fits 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 AIS equipped vessels | Alert Search & Rescue authorities |
What the person carries | Dedicated beacon, commonly fitted to a lifejacket | Dedicated personal distress beacon | |
Does it activate automatically? | Yes. Any sustained loss of connection between the phone / watch and DataHub Pro triggers MOB alert. | On some compatible models / installations, commonly when an inflatable lifejacket deploys. | Generally manual. |
Alerts your own crew onboard | Yes. Alerts activate on all phones / watches onboard with MOB app open or active in the background. | Yes. When received by compatible AIS / DSC equipment aboard. | No. Normally not directly. |
Audible warning aboard | Yes. All connected phones / watches with the app installed receive a loud, persistent alert. DataHub Pro triggers a MOB alert on MFD. | Typically yes when supported by the receiving AIS/MFD/DSC equipment. | Not inherently. |
MOB shown on chartplotter | Yes. | Yes, on compatible AIS equipment as an AIS MOB target. | Not with a conventional 406 MHz PLB. |
MOB position source | DataHub Pro GPS source, i.e. the boat's most precise GPS. Position set at the location where the device first lost contact with the DataHub Pro/Boat. | 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 VHF radio range; some devices also support DSC. | Not directly. |
Alerts shore contacts | Yes. Email and SMS alerts sent 120s after loss of contact to all Emergency Contacts set up via any available Internet connection to the DataHub Pro. No limit to how many Email / SMS contacts can be set. SMS sent to contacts in 80+ countries. | Not normally. | Alerts are handled through the international Search & Rescue system rather than personal email/SMS contacts. |
Alerts a Rescue Coordination Centre | No. | No. | Yes. This is the PLB's key role. |
Alert Type | Onboard contacts via DataHub Pro Wi-Fi. Shore contacts via Email / SMS through the internet. | 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 for all crew carrying a phone or watch with the app installed and in use. | Broadcasting the casualty's own position locally to equipped vessels. | Direct access to the international Search & Rescue system. |
Key trade-off | Sends a false alarm to all crew onboard with monitoring active if the DataHub Pro or crew device loses power. | Requires the person carrying the beacon and its signal being received within VHF radio range. | Normally requires the person to activate it and may not alert your own boat immediately. |
Where DataHub Pro Man Overboard fits
DataHub Pro Man Overboard is designed around the first critical problem in an MOB emergency: Do all the crew aboard know 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 after 10 seconds.
After ~ 30 seconds, all devices connected to DataHub Pro alert.
After ~ 60 seconds, the MOB event activates onboard via NMEA2000 (N2K). This triggers the MOB alert function on all onboard MFDs/chartplotters and places an AIS target on their chart as a waypoint.
After ~ 120 seconds, MOB Alert Contacts are alerted by email and SMS text message.
This means:
A phone or watch may also be carried by all crew throughout normal life aboard, providing peace of mind while the crew on watch have set their device and MOB app to active monitoring.
A crew member does not need to manually press a distress button for the DataHub Pro to detect that their monitored device has disappeared from the boat's Wi-Fi network.
Crew do not need to activate the MOB function of the MFD / chartplotter to create an AIS MOB target.
Crew can focus on immediate recovery and response coordination, not alerting fellow crew members to the MOB emergency event.
Where an AIS MOB beacon fits
An AIS MOB beacon travels with the person and transmits their position over AIS. Your yacht and other AIS-equipped vessels within VHF range may then see the casualty’s position.
Some models can activate automatically when an inflatable lifejacket inflates.
Where a 406 MHz PLB fits
A PLB alerts Search & Rescue via the Cospas-Sarsat satellite system. GNSS-equipped PLBs can also transmit the casualty’s position.
Unlike AIS MOB, a conventional PLB does not normally show the casualty as an MOB target on your yacht’s chartplotter.
What about combined AIS and 406 MHz beacons?
Some personal beacons combine both systems, providing local AIS MOB alerting and a 406 MHz satellite distress alert to Search & Rescue.
Check the individual beacon for activation method and lifejacket compatibility.
What about range?
They work differently, so there isn’t one useful range comparison:
DataHub Pro MOB: Detects when the monitored device loses connection with DataHub Pro.
AIS MOB: Broadcasts the casualty’s position over VHF/AIS to suitably equipped vessels within radio range.
PLB: Uses the 406 MHz satellite system to alert Search & Rescue.
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, watch keeping 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 well documented and practised 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 crew member.
Recovery — have a well documented MOB 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 departure. 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?