Ask Ken: Man-Overboard Electronics

Learn how to use marine electronics to save a man overboard.

March 23, 2018
Man-Overboard Electronics
Rescuing a Man Overboard Boating Magazine

Q. What electronics can be used in a man-overboard situation?

A. You can activate the MOB (man overboard) function found on most GPS/chart plotters. It will mark where the incident occurred and automatically plot a course back to that exact location.

Personal AIS (automatic identification system) transmitters like the McMurdo S20 ($249) transmit a signal that triggers an audible alarm on all AIS-equipped boats and ships within a 4-mile radius and places a flashing icon on navigation screens of the MOB incident.


Some newer personal MOB devices like the ACR AISLink MOB ($335) combine both an AIS and DSC (digital selective calling) to signal both AIS sets and DSC-equipped VHF radios.

The Ocean Signal MOB1 ($270) also transmits dual AIS and DSC emergency signals. When fastened to a life jacket, the MOB1 automatically sends emergency alarm signals unassisted when the life jacket is inflated.

Handheld waterproof, floatable VHF radios, such as the Icom M93D ($299) or Standard Horizon HX870 ($249), with built-in GPS can send a Mayday alarm with position coordinates with a push of a button. You also have the added benefit of being able to talk directly to rescuers or any boat in the area.


A PLB is a mini EPIRB and is great in an emergency situation when you are on a boat or raft. If you have a waterproof model and find yourself in the water and attempting to stay afloat, you can alert rescuers. But keep in mind that PLBs, like EPIRBs, cannot notify nearby boats, and it can possibly take up to several hours for first responders to reach you depending on your location.

Smartphone MOB
The CrewWatcher emergency radio beacon from Weems & Plath consists of a wearable MOB device that is water-activated when immersed in water or it senses that the beacon has moved away from the boat.

The CrewWatcher operates through a smartphone or tablet and a free downloadable app. It can also operate as a wireless water-level alarm in your bilge. Since it is water-activated, it can serve as a safety alarm for children and pets should they fall overboard. It can also alert you if a beacon is placed in a towed dinghy should it slip loose and drift away.


A CrewWatcher kit with one beacon costs $90 and $170 with two beacons.

Electronic SOS Beacon Lights
Visual contact in an MOB situation can be quickly lost with darkness and wave action. Weems & Plath has an electronic flare with its SOS Distress Light, Model C-1001 ($100). Operating on three C-cell alkaline batteries, it flashes a bright strobe light in a coded sequence messaging “SOS” in internationally recognized Morse code that can be seen up to 10 nautical miles away. This waterproof, buoyant MOB strobe light floats and marks the spot where the MOB incident occurred. The MOB Distress Light is completely electronic and nonpyrotechnic.

Ocean Signal also has a handheld nonfloatable personal MOB device. The ME MOB1 ($140) transmits AIS and DSC signals simultaneously, produces a bright strobe light for visual identification in the water, and integrates well with life jackets.


While a little large for a personal MOB device in most situations, the McMurdo E8 and the Kannad Safe Pro series of EPIRBs integrate a GPS and AIS beacon that can broadcast a worldwide Mayday to first responders along with an AIS signal to alert nearby boats in the area that an emergency distress exists and also send the coordinates for the MOB location (available first quarter of 2018). You can expect to see combination PLB devices with AIS to be available in the future.

Practice Ahead of Time
Remember that prudent seamanship dictates that you familiarize yourself with the operation of your boat’s safety equipment before an emergency occurs. Refer to you owner’s manual to ensure your understanding of how to activate the device, along with its capabilities and limitations.

Run a simulated MOB situation on your next boat outing. Designate someone aboard to throw a life jacket in the water at a time of their choosing and yell, “Man overboard!” Then see how quickly you can activate your navigation display’s MOB function and return to that position.


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