Why carry a locating device/beacon?

Having a locating device could be the difference between being recovered or being lost at sea. Once in the water, there is only a 40% chance of being recovered. Any device that will increase the chance of survival is strongly advisable.

Personal Locator Beacons (PLBs)

Personal Locating Beacons (PLBs) are effectively a smaller portable EPIRB and transmit on 406MHz distress alert via the COSPAS-SARSAT satellite network. Once activated the signal is sent to a Mission Rescue Control Centre where it is decoded and forwarded to the nearest local Rescue Coordination Centre. This centre will then attempt to contact the registered details to determine the nature of the distress situation. Once the alert has been verified a rescue plan is formulated and the aircraft and/or vessels are dispatched.

PLBs Pros and Cons

This verification process takes on average up to 45 minutes. PLBs are available with or without integral GPS. Integrated GPS significantly reduces the search area to within 100m. Units without GPS (or where the GPS is unable to get a fix due to an obstructed view of the sky), then initial location will be performed by orbiting satellites. This could take up to a number of hours depending on location and with a typical accuracy of 2-5 km.

A PLB does not rely on a vessel being within VHF range to receive the emergency distress signal. It simply relies on the beacon being activated, functioning and being registered correctly.

PLBs, however, are only manually activated therefore if the man overboard is not conscious the PLB is ineffective. Also if the visibility is restricted the casualties own vessel, or vessels in the vicinity will not be able to locate the person if they lose sight of the casualty.

However, for vessels that regularly operate outside reliable VHF range, a 406MHz beacon should be considered an essential piece of equipment, rather than a desirable extra, particularly for long-range cruising boats.

AIS locating device

AIS locating devices are the most accurate tracking and locating technology available. They can be combined with satellite systems, such as GPS, providing a continuously updated position, COG and SOG up to eight times a minute. The AIS alert signal is transmitted to all AIS receivers and AIS enabled chart plotters up to an 8-mile radius, depending on the height of the antenna. AIS locating devices are both manually and automatically activated.


AIS locating devices are now also available with an open-loop VHF DSC alerting function using a DSC Distress alert Mayday All Ships Alert. Each locating device has an individual MMSI number for fast identification and enabling tracking of multiple Man Overboard (MOB) casualties. It works within a line of sight radius from where the signal is activated and communicates with all existing VHF DSC radios on board any vessel. If it is, however, closed-loop DSC it will only alert on pre-programmed VHF DSC radios. The GPS coordinates are displayed on the VHF and updated frequently to give you constant pinpoint tracking functionality.

AIS locating devices combined with DSC provides the quickest chance of recovery, in an area where there are other vessels carrying AIS receivers. This is mandatory for all vessels over 300gt and a high percentage of leisure craft have opted to do carry them too.


A distress alert will provide a good initial location to search for the survivors, especially if it has integrated GPS.  All PLBs, and some AIS locating devices, incorporate additional transmitters operating on 121.5MHz. This frequency, however, requires Direction Finding (DF) equipment that is typically carried by SAR helicopters and lifeboats. The DF equipment homes in on the frequency aiding detection of smaller targets. However, this DF equipment is not typically carried by commercial or leisure vessels who may be the first at to the scene.

The key considerations when choosing between AIS or a PLB :

  1. The type of sailing/fishing you do – offshore, coastal, single-handed, in busy or remote areas
  2. PLB with, or without, integral GPS
  3. Multiple technologies to increase the chance of recovery, 121.5MHz, DSC closed loop of open-loop for full all ships alert
  4. The battery life (how long the beacon will transmit after it is activated)
  5. Manual or automatic activation

The Weatherdock AIS safety range has been designed to meet the international safety standards and uses a combination of AIS GPS, VHF DSC and 121.5MHz technologies to give your crew the greatest chance of survival in the event of a Man Overboard situation.

Click here to view our locating devices