Getting rescued at sea requires two things working in sequence: someone knowing you are in trouble, and someone knowing where you are. Modern electronic distress beacons have transformed both of these problems. A properly registered, properly maintained EPIRB can put a rescue-capable asset at your location within hours from virtually anywhere on the ocean. But the system has requirements, failure modes, and dependencies that sailors who rely on it must understand.
Electronic beacons are not a replacement for seamanship or passage planning. They are a last resort that is dramatically better than every previous last resort. Understanding how they work — and what undermines them — is as important as simply having one aboard.
EPIRB vs. PLB vs. SART: What Each Device Does
These three devices are frequently confused, and the confusion matters because they serve different purposes and have different operational profiles.
An EPIRB (Emergency Position-Indicating Radio Beacon) is the vessel's distress beacon. It is registered to the boat, it is larger than a PLB, and — in its Category I form — it is designed to automatically activate and float free if the vessel sinks. EPIRBs are the primary distress alerting device for offshore vessels. They transmit on 406 MHz to the Cospas-Sarsat satellite network and include an integrated GPS receiver that allows the system to report your position to rescue coordination centers with an accuracy of approximately 100 meters.
A PLB (Personal Locator Beacon) is the individual's beacon. It is smaller — some PLBs are genuinely pocket-sized — uses the same 406 MHz Cospas-Sarsat network, and is registered to a person rather than a vessel. PLBs must be manually activated; they do not auto-release. For offshore sailing, a PLB worn on your person means that if you go overboard and your boat sails on (or sinks with everyone else aboard), you still have a distress signal capability. A PLB on the boat's EPIRB bracket, not on a crew member's body, provides no benefit if the crew is separated from the vessel.
A SART (Search and Rescue Transponder) is a different device entirely: it is a radar transponder that, when activated, responds to the radar pulses of aircraft and vessels engaged in the search. On their radar screens, SAR assets see a distinctive line of dots leading to your position. SARTs are not connected to the satellite network and provide no initial alert — they are a homing device for SAR assets who already know roughly where you are. A SART is used in conjunction with, not instead of, an EPIRB or PLB. AIS-SARTs (which also transmit an AIS target) are increasingly common and provide the same homing function visible on AIS chartplotters aboard nearby vessels.
How the Cospas-Sarsat System Works
When your 406 MHz beacon activates, it transmits a coded signal that includes your beacon's unique 15-digit hex ID (and, with GPS enabled, your precise position). This signal is received by Low Earth Orbit (LEO) satellites and Medium Earth Orbit (MEO) satellites in the Cospas-Sarsat constellation. The satellite network relays the signal to ground stations, which forward it to Mission Control Centers (MCCs), which in turn notify the appropriate Rescue Coordination Center (RCC) for your region — in the United States, that is one of the U.S. Coast Guard's district coordination centers.
The time from activation to first fix varies with satellite geometry and GPS availability. With GPS integrated and functioning, a modern 406 MHz beacon can provide a position fix accurate to 100 meters within approximately 45 minutes, often faster. Without GPS (GPS failure, or older non-GPS beacons), the Doppler positioning process takes longer and is less precise — accuracy drops to 2–5 km. This is the practical argument for ensuring your beacon's GPS is functional before departure.
Once the RCC has your position and beacon registration data, they can immediately look up your vessel name, type, home port, emergency contacts, and the description of your boat. This information dramatically accelerates the dispatch and identification of the appropriate SAR response. An RCC that receives an alert from an unregistered beacon has none of this — they dispatch resources to a position they cannot confirm is a real emergency, burning aviation fuel and risking rescue crews based on incomplete information.
Registration: Not Optional
EPIRB and PLB registration is free, takes minutes online, and is among the most consequential safety steps you can take before an offshore passage. In the United States, register your beacon at the NOAA Beacon Registration database (beaconregistration.noaa.gov). In Canada, register with the National Search and Rescue Secretariat. Update the registration when your vessel information changes — different boat, different home port, different emergency contact.
Unregistered beacons are a serious problem for the SAR system. The USCG reports that a substantial proportion of 406 MHz alerts it receives come from unregistered beacons — meaning SAR assets are dispatched to investigate alerts where they have no vessel information, no emergency contact to call to confirm the situation, and no way to determine quickly whether the activation is real or accidental. Every unnecessary SAR response uses resources that may be needed for an actual emergency.
After registration, test your beacon periodically using the self-test function (which transmits a test signal detectable by the beacon itself but does not transmit to the satellite network). Do not activate your beacon for live testing outside of the designated first five minutes of the first hour of each UTC hour — that is the official test window for brief real transmissions, though self-test is preferred.
Category I vs. Category II EPIRBs
This distinction matters and must be understood before departure.
A Category I EPIRB is mounted in a hydrostatic release bracket designed to automatically release the beacon when submerged to 1–4 meters. If the vessel sinks with the EPIRB in its bracket, the beacon floats free, activates automatically, and begins transmitting. This provides distress alerting even if the crew is incapacitated or the sinking is sudden. Category I is the appropriate choice for offshore and blue-water sailing.
A Category II EPIRB must be manually activated. It can be mounted in a bracket or stored below, but it will not activate automatically. If you are unable to reach it — incapacitated, swept overboard, trapped below — it will not transmit. Category II is appropriate for coastal use where the crew has time to act; it is a compromise for offshore passages.
Battery and hydrostatic release mechanism replacement schedules are printed on the device and must be followed. An EPIRB with an expired battery or a fouled hydrostatic release is a false confidence item — it looks like protection and provides none. Check the expiration dates before every offshore season.
The MAYDAY Protocol
A MAYDAY call on VHF Channel 16 is your primary distress communication for situations involving imminent danger to life. The sequence is fixed. Knowing it before you need it means you can transmit it clearly when you are frightened, injured, or watching your boat sink.
The standard MAYDAY format:
MAYDAY MAYDAY MAYDAY — three repetitions, unambiguous.
THIS IS [vessel name] [vessel name] [vessel name] — three repetitions of your vessel name.
MAYDAY [vessel name] — one more time, to begin the message body.
MY POSITION IS [position] — GPS coordinates in degrees and decimal minutes, or a bearing and distance from a known landmark. Be as precise as possible.
I AM [nature of distress] — sinking, on fire, man overboard, medical emergency.
I HAVE [number] PERSONS ABOARD — total souls aboard.
I REQUIRE IMMEDIATE ASSISTANCE.
[Brief description of vessel] — type, length, color of hull, any distinguishing features.
OVER — indicate you are releasing the transmit button and listening for a response.
Transmit on Channel 16, which is monitored continuously by the U.S. Coast Guard and most commercial vessels. If no response after two minutes, repeat. A DSC (Digital Selective Calling) distress button on a properly connected VHF radio sends a digital MAYDAY alert with your MMSI and GPS position automatically — press and hold the DSC distress button for five seconds, then follow up with a voice MAYDAY on Channel 16.
Pan-Pan: Urgency Without Immediate Danger
Not every emergency requires a MAYDAY. The PAN-PAN call (pronounced pahn-pahn) is the urgency signal — it declares that you have an urgent situation that requires assistance but does not yet represent an immediate threat to life. A significant engine failure, a medical situation requiring guidance but not evacuation, a vessel taking on water but not in immediate danger of sinking — these are Pan-Pan situations. The format mirrors MAYDAY: PAN-PAN PAN-PAN PAN-PAN, vessel name, position, nature of the urgency, souls aboard, OVER. Pan-Pan gets attention and assistance without the full SAR mobilization of a MAYDAY.
Visual Distress Signals
Electronic systems can fail. Visual signals are the backup and the complement to electronic alerting, and they are specifically effective once a SAR asset is in the vicinity and searching for you.
Parachute flares (rocket flares): SOLAS-approved parachute flares burn at 300 meters altitude for approximately 40 seconds and are visible for up to 30 miles in good visibility. They are the most effective visual signal for establishing initial contact with a searching aircraft or distant vessel. The minimum offshore kit is three. They expire — check dates before passage.
Handheld red flares: Burn for one minute at close range. Most useful when a SAR asset is nearby and you are providing a precise homing signal. Minimum kit offshore is three. Handle with care — they are extremely hot and burn through gloves.
Orange smoke signals: Handheld or floating; daylight use only. Orange smoke is highly visible from aircraft and effective in low-wind conditions. In strong wind, the smoke disperses quickly. Standard kit includes two floating orange smoke signals.
Orange distress flag: Required on recreational vessels as part of the visual distress signal kit in some jurisdictions. Visible by aircraft in daylight; passive and requires no activation.
Mirror signaling: A heliograph or signal mirror can reflect sunlight visible to aircraft at up to 10 miles in good conditions. They require sun and clear sky, cost nothing, have no expiry, and require practice to aim effectively. Carry one and know how to use it.
Effective distress signaling combines layers: activate the EPIRB immediately, get on Channel 16 with a MAYDAY, fire parachute flares when you hear or see an aircraft, use handheld flares when the SAR asset is close, and have orange smoke ready for the final approach. No single signal is sufficient; the combination is what gets you found.