Schedule a demo to enter to win free SeaKits Essentials


Taking The “Search” Out Of Search & Rescue


Connecting to a constellation of satellites and rescue assets, today’s modern, highly accurate GPS-equipped EPIRBs and PLBs could be your lifesaver in an emergency. Here’s how they work.

Today’s GPS-equipped Personal Locator Beacons (PLBs) and Emergency Position Indicating Radio Beacons (EPIRBs) are accurate, fast, and portable. Since 1982, EPIRBs and PLBs have helped to save more than 35,000 lives around the world. That’s how rescue can work today, with the right equipment and the right information.

Here’s how a modern GPS-equipped emergency beacon reduces search time. Once activated (see “What You Need To Know About EPIRBs & PLBs” below), an EPIRB or PLB broadcasts a 406-MHz message, with your vessel’s unique identification code, to two different satellite systems. The first, and original, array is the Low Earth-Orbiting Search And Rescue (LEOSAR) system, which can detect and locate 406-MHz alerts worldwide as its satellites pass over the Earth’s surface. The satellite’s equipment also transmits your information to special land-based terminals as soon as it comes within range (around 2,500 miles). Even if your emergency beacon does not transmit your GPS position, these satellites, in conjunction with their terminals on land, can determine your location by measuring the Doppler shift of your signal (see “Frequently Asked Questions”). The initial Doppler shift position can be off by many miles, but with each pass of the satellite over your distress signal, about once every 100 minutes, your position is refined. Obtaining a reliable position for a distressed vessel can take two hours or more, and that position is only accurate to a mile or more, resulting in a 4.5-square-mile search zone.

Personal Locator Beacon (PLB) with GPS can
dramatically reduce rescue times.

What You Need To Know About EPIRBs & PLBs

When there’s a life-threatening problem aboard your boat, an EPIRB can be your lifesaver. Intended for marine use only, EPIRBs are even required for some fishing tournaments and sailboat races. All EPIRBs are required to float in an upright transmitting position, have both a manual- and automatic-activation feature, and have a battery that is required to signal for at least 48 continuous hours. Depending on features, EPIRBs start at around $600.

In some ways, a PLB is like a small EPIRB and uses the same satellite network to dispatch appropriate SAR agencies. PLBs have no requirement to float or to have a strobe light, but many do. They, like EPIRBs, have a homing signal to help SAR teams zero in on your position, and are required to signal for no less than 24 hours. Some boat owners have an EPIRB registered to the boat, and PLBs available for the crew, which also should be registered with boat information given. Also great for people on small boats or kayaks, the PLB’s compact size makes them ideal to attach to your life jacket, or belt, place in your pocket, and go anywhere you go.

PLBs must be activated manually so you must be conscious to use them. A PLB may be more likely than an EPIRB to miss “seeing” a satellite and getting a GPS fix because it may be in the water with the user who may not position it properly, at least temporarily. However, an EPIRB, even if in an automatically releasing bracket, may go down with the boat in a severe emergency. Prices for PLBs start at about $250. At least one manufacturer will email you self-test results and a limited number of location-confirmation messages to five personal contacts. Both EPIRBs and PLBs are now available with an invaluable GPS-equipped feature.

— Ted Sensenbrenner

The other satellite system at work is the Geostationary Orbiting Search and Rescue (GEOSAR), whose satellites orbit with the Earth and remain in fixed positions over it. As long as you’re between about 70 degrees N and 70 degrees S, these satellites receive your beacon’s information and transmit it to a ground terminal almost instantaneously. They can’t calculate a position using Doppler shift, however, because they’re not moving. The only way they can provide your position information is if your emergency signal includes your GPS position.

Your Beacon Matters

Older beacons — and many models still sold today — are unable to transmit a vessel’s GPS coordinates, leaving the Doppler shift as the only way to determine a position. Instead of two hours and a position accurate to a bit over a mile using the LEOSAR Doppler shift calculations, today’s GPS-equipped beacons can transmit your position within five minutes directly to the satellites with an accuracy of 100 meters — just over the length of a football field. Considering visibility from search aircraft can be less than a mile in severe weather conditions, that’s a significant improvement.

Using older emergency beacons, not equipped with GPS, it took a long time to come to a relatively inexact location; plus, older beacons were expensive. Two decades ago, their use was limited to boats heading out to cross oceans. But today’s GPS-equipped beacons cost as little as $250, and their impressive accuracy can assist with rescue anywhere. Of the 644 emergency signals worldwide in 2011, only half came from boats. The rest were almost equally divided between aircraft and shore-based beacons carried by hikers, snowmobilers, off-roaders, and other back-country adventurers. Of the marine-distress signals in U.S. waters in 2011, three-quarters occurred within 50 miles of shore; one-third were 10 miles or less from shore. In a half-dozen emergency situations in 2011, victims already in radio contact with the Coast Guard were asked to turn on their EPIRB or PLB to assist in locating them.

Frequently Asked Questions

What is Doppler shift?

Imagine hearing a siren on an approaching police car. The pitch sounds higher as the car gets nearer, and lower as the siren passes — all due to sound waves. The equipment on the LEOSAR satellite senses the wave shift from the beacon’s signal as the satellite moves closer to farther from the beacon, then utilizes this shift to calculate its distance from the beacon.

Can’t I just use my cell phone to send emergency info?

Cell phones are no substitute for modern GPS-equipped 406 EPIRBs or PLBs. They must be within range of a tower, often are not waterproof, and don’t give a continuous signal that will be picked up by an RDF on a rescue vessel. However, if you have a signal, and the circumstances allow cell phone use, do it. A better alternative may be to use your properly connected, programmed, and registered VHF if in range, which will tell the Coast Guard who you are, and what boat you are on. Depending on the nature of your distress, the Coast Guard may have you shift communications to a cell phone, or activate your EPIRB or PLB, to assist in locating you and to be sure they don’t lose contact if your cell phone or VHF dies or you lose the signal.

How do different countries work together on a rescue?

The entire SAR system is an international program called Cospas-Sarsat. When a distress signal is received, it’s relayed to the Mission Control Center nearest to the activated beacon, regardless of the nationality of that center. The center then coordinates with the beacon’s country of registry to verify the signal.

What if a commercial ship is closer to my position?

Through the worldwide Automated Mutual-Assistance Vessel Rescue System (AMVER), Coast Guard personnel will ascertain if an AMVER-participating commercial ship is in the vicinity of the distress situation, look at the ship stats, and determine if it should be dispatched to help.

Are false activations of EPIRBs a big problem?

The registration requirement allows rescuers to verify a signal before putting people and equipment at risk. Over 90 percent of 406-MHz signals are not emergencies; 85 percent of these are resolved using registration information before any search is undertaken. Most of these false signals result from accidental activation or water triggering an automatic EPIRB, as when a vessel sinks at the dock; a few involve hoaxes. Any false signal can lead to serious injury and loss of life of rescue personnel, and draw assets away from truly distressed boaters. The FCC prosecutes misuse. Unlike cell phones and other devices, you don’t “activate” your beacon until the emergency; beacons have a test feature so you can make sure they are functioning.

Meanwhile, Back On Land

The land terminal (or terminals) to which the satellites transmit your information is essentially a big antenna with a special computer that transmits the distress information to the network of Mission Control Centers around the world (for typical U.S. situations, the MCC is in Maryland). Computers at the appropriate MCC collect and process the distress data and transmit it to the closest Rescue Coordination Center to you that has assets to handle the rescue. Coast Guard personnel assess the information, determine if it’s an actual emergency, then call for the launch of a plane, helicopter, or boat.

Whenever any information changes or you’re traveling beyond your normal home waters, make sure to update your contact person with your itinerary, the crew aboard, and any other details that might be helpful if rescue personnel are called in an emergency situation. Also, update the “Comments” block on the NOAA beacon registration website (it takes about 10 minutes) with the same information. You might submit, for example, that between certain dates you’ll be traveling between Narragansett Bay and Delaware Bay. When Coast Guard personnel get your distress message, they’ll go to the info you’ve posted online and try to reach your emergency contact. If the distress info coming from the beacon puts the boat in the same area described in your comments and/or confirmed by your emergency contact, they’ll know the emergency is real and — possibly within minutes — dispatch a boat or plane.

New Ways Of Zeroing In

As the rescue aircraft or vessel nears your vicinity, the rescue crew begins looking for your boat, or for people in the water. But even the “football-field radius” information from your beacon’s GPS still covers a lot of area in which to find a tiny target, especially in waves or poor visibility. 406-MHz EPIRBs also transmit a signal on a frequency of 121.5 MHz, and once in the vicinity, searchers home in on that using a Radio Direction Finder (RDF) to locate the vessel. But the 121.5-MHz signal is far less powerful and has a much shorter range than the 406-MHz transmission.

An hour and a half after activating his EPIRB, Kevin Savage and his cat were rescued by the USCG off the coast of Georgia, after their sailboat began taking on water. (Photo: U.S. Coast Guard)

The U.S. Coast Guard began equipping its search-and-rescue planes with 406 MHz Radio Direction Finders (RDF), which can home in on the 406-MHz signal from your beacon, a few years ago. Retired USCG Captain Dave McBride has flown dozens of missions in search of distressed vessels in the U.S. rescue area, which extends 600 nautical miles from shore. “I could direction-find off a 406-MHz signal from 120 miles out,” he said. “But with 121.5-MHz, I might not be able to find it until I was five miles away.”

Rowers Adam Kreek, Jordan Hanssen, Patrick Fleming, and Markus Pukonen were rescued after their 29-foot rowboat capsized, ending their trans-Atlantic attempt. (Photo: Erin J. Hale)

That capability turns a needle-in-a-haystack search into a surgical extraction. Last year, a 29-foot boat powered by four rowers attempting a record-breaking journey from Senegal in Africa to Miami, Florida, was capsized by two large waves 850 miles short of its destination. At 6:30 a.m., Coast Guard Station San Juan detected four signals, one from each rower’s ACR ResQLink PLB, about 380 miles north of Puerto Rico, confirmed the boat’s location through the registration information, and coordinated the launch of two aircraft to search for survivors. An HC-144 Ocean Sentry flying out of Clearwater, Florida, picked up the 406-MHz signal from more than 70 miles out and, just four-and-a-half hours after the EPIRB had been activated, located the life raft with all four men safely onboard. Shortly before sunset, the men were taken onto an AMVER-participating commercial vessel (see “Frequently Asked Questions”). Though the capsize occurred hundreds of miles from shore, only a third of the time from beacon activation to rescue had been spent on the search.

A Peek At The Near Future

The number and type of satellites, equipment onboard, and other phases of the system are improving continuously. For example, SAR packages are being placed on newly launched GPS satellites called MEOSARs (mid-Earth orbiting SAR satellites). The combined MEOSAR paths will look more like a web around the world compared to the relatively narrow bands of coverage of the LEOSAR and GEOSAR satellites. This development will result in near-instantaneous position fixing and alerting because of the number and placement of orbits, and other advancements. MEOSAR is scheduled to be operational in 2018. Standards for the next generation of beacons are set to be updated by 2015, and beacons being sold today will continue to work with newer systems, according to the USCG Office of Search and Rescue.

The beacons we carry aboard and the satellite systems that detect and transmit their emergency signals continue to evolve, as state-of-the-art GPS-equipped EPIRBs and PLBs, and the registration information that goes with them, allow rescuers to skip the search and focus in on the rescue, hopefully shortening that harrowing wait when an emergency strikes.

Want To Rent One?

The BoatUS Foundation, in partnership with the Coast Guard and NOAA, rents GPS-equipped PLBs and EPIRBs for $45 and $65 a week, respectively, plus shipping. To date, through our program, there have been 30 emergency activations with more than 60 boaters rescued. The BoatUS Foundation collects vessel description, itinerary, and emergency contacts as part of the rental agreement, and shares this with the USCG in the event of an activation. To rent, visit or call (888) 663-7472.

Tom Neale

Technical Editor, BoatUS Magazine