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EPIRB Rental Program

Boat Tech Guide: 406 MHz EPIRB

Emergency Rescue Beacons - updated February 2009
by Chuck Husick

Marine Emergency Position Indicating Rescue Beacons, EPIRBs came into general use by recreational boaters beginning in the early 1970s. A Federal law was passed requiring that all general aviation aircraft equip with an emergency locator transmitter (ELT). These emergency radio beacons included acceleration (g) sensitive switches intended to automatically activate the beacon in the event of a crash. It was obvious to many that with substitution of a manual activate switch for the "g" switch and appropriate waterproofing these beacons would be useful on boats, especially on the high seas. These ELTs and EPIRBs transmit simultaneously on the international civilian and military VHF /UHF distress frequencies, 121.5 and 243.0 MHz, that are monitored by aircraft in flight. In addition, the COSPAS / SARSAT satellite based monitoring system, a cooperative effort of the United States and the Soviet Union could monitor these emergency frequencies and relay distress signals provided the signal was heard while the satellite was in contact with a ground monitoring station. The satellites could not store received signals for later transmission to the ground. The system worked well, and was credited with numerous rescues. However, the proliferation of EPIRBs and ELTs and their improper storage and use led to an excessive false alarm rate. In addition, the transmitted signals carried no unique identification information, making it impossible to determine if the signal was a genuine call for assistance or the result of accidental activation of the beacon. Further, the monitoring system precluded rapid localization of the origin of the signal, often resulting in protracted search efforts before the beacon was located. Satellite monitoring of 121.5 / 243.0 MHz beacons has been discontinued. Although such beacons may still be used their effectiveness is very limited and should if at all possible be replaced with 406 MHz beacons.

The limitations of the 121.5 / 243.0 MHz system led to the development of today's 406.0 MHz based ELT / EPIRB system. The 406.0 MHz units transmit a much stronger signal that includes the unique serial number built into each device. The signals are monitored by a combination of satellites, including both the polar orbiting satellites of the COSPAS/ SARSAT system and geostationary satellites capable of re-transmitting precise position information incorporated in the message transmitted by EPIRBS containing a GPS receiver or connected to an external GPS or Loran C navigator. An emergency signal from a 406 EPIRB is usually noted within a few minutes of being transmitted. The position of the EPIRB is normally known to within a few miles, greatly simplifying search and rescue efforts. The position of an EPIRB transmitting a GPS derived position is precisely known. In addition to the 406.0 MHz signal, the 406 EPIRB transmits a homing signal on 121.5 MHz for the purpose of guiding nearby search aircraft and vessels to the precise location of the beacon.

The outstanding success of the 406 EPIRB system relies upon world-wide registration of all 406 EPIRBs. Beacons sold in the U.S. must be registered with the SARSAT Beacon Registration office at NOAA. Their web site, provides a wealth of information and includes means for downloading registration forms. Once a beacon is registered you are required to advise the SARSAT office of changes in address or telephone number. The SARSAT office will automatically send registration renewal forms every two years. The importance of the search and rescue system to immediately check on the likely validity of a 406 EPIRB signal cannot be overemphasized. Upon receipt of a 406 EPIRB signal the Coast Guard will check with those persons listed on the beacon registration form to ascertain the location and status of the beacon, ensuring that search assets are directed only to those beacon signals reasonably known to be valid calls for help. The results are more rapid and effective search and rescue work, at lower cost and with less risk to the lives of the rescue teams.

These EPIRBs are available in a number of styles, some with integral GPS receivers, others that connect to an external GPS. Ensuring that the EPIRB can transmit your vessel's position is highly recommended. Some have built-in strobe lights. All are waterproof. All will operate continuously for a minimum of 48 hours at below freezing temperatures and for a considerably longer period of time at the higher temperatures likely to be encountered by recreational boaters. In all events, an EPIRB, once turned on must be left on until a rescue is completed. Do not attempt to prolong battery life by operating the device intermittently. Doing so will reduce the rapidity of a successful search and rescue effort. Small 406 MHz Personal Locator Beacons, "PLB's" are available and will provide a very valuable additional level of security. Although battery life is somewhat shorter than that specified for EPiRBs they transmit the same type of signal and can be equally effective in notifying search and rescue authorities of your need for immediate assistance.

406 EPIRBs are available as manually deployed units or with deployment mechanisms that automatically activate should the vessel sink without warning. It is also common to pack a 406 EPIRB inside a life raft container or in an abandon ship bag or canister. A properly registered 406 EPIRB belongs on every vessel that ventures off shore beyond close-in VHF radio range, about 10 miles or operates in areas not served by Coast Guard VHF radio.

Your responsibility to your guests, crew and yourself does not end with the purchase of the EPIRB. You need to periodically check it, using the built-in test function, not by turning it on! You need to note the expiration date for its battery and ensure that a fresh battery is installed when needed.

The BoatUS Foundation provides mariners a unique and very valuable service, renting EPIRBs for periods of up to two weeks. The availability of this rental program eliminates any excuse for venturing offshore without a 406 EPIRB. This device is likely the most effective, lowest cost life insurance investment any mariner can make.

In addition to the 406 MHz EPIRB a number of personal EPIRBs, transmitting either on 121.5 MHz or on 418 MHz are available for use in possible man overboard situations. These small units are designed to be worn by on deck crew members. Their transmission range is typically limited to a mile or two and are used in conjunction with on-board alarm and direction finding receivers. These EPIRBs are typically designed to automatically begin to transmit if they are submerged or when triggered by the wearer. The on-board monitor receiver will sound an alarm, after which its direction finding capability greatly simplifies locating and homing in on the man in the water. Most sales of this type of system are to ocean voyaging sailors. Regardless of the type of 406 beacon you use it is critically important that once you turn it on you leave it on until assistance arrives or you have established contact with those coming to your aid and they have concurred with your turning the device off.

A Search and Rescue Transponder (SART) is a battery powered radar frequency receiver and transmitter. When operating, the SARTs receiver constantly scans the maritime radar frequencies, listening for a searching radar signal. Upon receipt of a signal, the SART transmits a varying frequency signal that will be received by any searching radar. The SART's signal is many times the strength of any reflection of the searching radar beam from a passive target, greatly enhancing the likelihood of detection. The screen image created by the SART signal is a unique pattern that points to the source of the reply, the SART on your vessel or life raft. Since SARTs may needed to aid a searching surface or airborne radar in locating a vessel they are normally carried as part of an abandon ship bag, not packed in a life raft.

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