Marine Emergency Electronics Explained

EPIRB, PLB, Garmin inReach

We get asked a lot of questions about marine emergency electronics systems, so as I am sailing around the Grenadines, I thought I would try to explain the different systems in simple, understandable terms.

There are lots of buzzwords and acronyms in use, and to add to the confusion, the technology has rapidly evolved over the last 50 years — first with satellite communications, then with GPS, and later with digital navigation systems.

Understanding the different types of marine safety electronics is essential for anyone sailing offshore or in remote areas.

VHF Marine Radio: The Foundation of Marine Safety Communication

Probably the most common safety electronics in use is the Marine VHF radio. They are robust, relatively low cost, and provide safety communications not only coastally but also offshore.

Technology

Marine VHF channels operate in the frequency range of 156.000 MHz to 162.050 MHz, utilizing 25 kHz channel spacing. They are divided into international, USA, and Canadian channel sets.

The channels are simplex (one directional) — hence the familiar “over” protocol — and now use vertically polarized FM modulation.

These frequencies travel only line-of-sight distances, so with a high Coast Guard tower and a large sailboat mast, the maximum range is about 30 nautical miles.

A good approximation for visual line-of-sight distance in nautical miles is: 1.2 × √ height of antenna (in feet)

For radio transmissions, we increase this slightly: 1.4 × √ antenna height

To determine range between two stations (for example a tower and a vessel), calculate each antenna height and add the two distances together.

Key VHF Channels for Safety

Important VHF channels every sailor should know include:

• Channel 16 (156.800 MHz) – International calling and distress channel monitored by all vessels

• Channel 70 (156.525 MHz) – Dedicated to Digital Selective Calling (DSC)

• Channel 13 (156.650 MHz) – Inter-ship navigation safety (bridge-to-bridge)

• Channel 06 (156.300 MHz) – Inter-ship safety communications

• NOAA Weather Channels (162.400–162.550 MHz) – U.S. weather broadcasts

• Channels 68, 69, 71, 72, 78 – Recreational communications

History of Marine VHF

Marine VHF radios evolved from World War II vessel-to-vessel communication systems operating in the UHF/VHF spectrum.

In 1947, the 156–157 MHz frequency band was standardized for maritime use and widely adopted in the 1950s.

During the 1960s, communication switched from AM to FM modulation, producing clearer sound and reducing interference. The number of available channels was also doubled to accommodate increasing maritime traffic.

AM communication for marine radio was finally discontinued in 1977.

Digital Selective Calling (DSC) and AIS

Digital Selective Calling (DSC) was introduced in the 1980s as a faster and more reliable way to send distress alerts than voice communication.

Channel 70 became the dedicated digital hailing channel, and all new VHF radios sold after June 1999 were required to include DSC capability.

Automatic Identification System (AIS)

AIS was developed in the 1990s to overcome limitations of radar, which can detect vessels but cannot identify them.

AIS allows vessels to broadcast:

• Position

• Identity

• Course and speed

• Navigational status

AIS uses dedicated channels:

• 161.975 MHz (87B)

• 162.025 MHz (88B)

These continuously transmit navigation information to other vessels.

AIS and Satellite Integration

In the 2000s, AIS became mandatory for SOLAS (Safety of Life at Sea) vessels.

Lower-cost Class B AIS radios were later introduced for recreational boats, while Class A systems can relay signals via satellite.

This means that if a recreational vessel is within 20 miles of a commercial ship, its AIS information can be automatically relayed to satellites — allowing AIS tracking even in mid-ocean.

Modern DSC and AIS systems are now part of the Global Maritime Distress and Safety System (GMDSS) used for distress alerts, vessel tracking, and emergency coordination.

EPIRBs: Emergency Position Indicating Radio Beacons

An EPIRB (Emergency Position Indicating Radio Beacon) is one of the most critical pieces of safety equipment on a vessel.

History of EPIRBs

The first EPIRB was developed in 1970, transmitting on 121.5 MHz and 243 MHz to alert nearby aircraft of vessels in distress.

However, these early models lacked precise satellite positioning.

In the 1980s, the Cospas-Sarsat satellite search and rescue system began detecting EPIRB signals globally, although accuracy was limited to about 20 kilometers.

The introduction of 406 MHz EPIRBs in the 1990s greatly improved detection and reliability.

By 1992, the International Maritime Organization required commercial vessels to carry 406 MHz float-free EPIRBs.

How Modern EPIRBs Work

Modern EPIRBs contain several technologies:

• 406 MHz transmitter (5 watts) for satellite detection

• 121.5 MHz transmitter (0.25 watts) for homing signals

• GPS receiver to provide precise location data

• AIS transponder to broadcast position to nearby vessels

Once activated — manually or automatically by water immersion — the EPIRB transmits a signal detected by satellites approximately 24,000 miles above Earth.

The signal includes the beacon’s serial number and GPS coordinates, allowing the Coast Guard to quickly identify the vessel and its location.

Rescuers can then home in on the signal using 406 MHz, 121.5 MHz, or AIS broadcasts.

Be aware, that if you have an older EPIRB without a GPS transmitter, it may take a lot longer for the emergency services to respond, leading to several incidents where the captain would have taken a different course of action if he knew that his distress signal was not being responded to immediately.

Personal Locator Beacons (PLBs)

Personal Locator Beacons (PLBs) are similar to EPIRBs but are designed for individual use rather than vessels.

PLBs have evolved from simple emergency transmitters into multi-function satellite safety devices.

Modern PLB Technology

Today’s PLBs typically include:

• 406 MHz transmitter connected to the Cospas-Sarsat satellite network

• GNSS/GPS receiver for accurate location transmission

• 121.5 MHz homing signal for precise rescue operations

• AIS broadcast so nearby vessels can see the distress signal

• Return Link Service (RLS) confirming that the alert has been received

• NFC smartphone connectivity for testing and diagnostics

• Automatic activation with life jackets

• Infrared and visible strobes to assist rescuers at night

• Battery life of up to six years

History of Personal Locator Beacons

PLBs evolved from Emergency Locator Transmitters (ELTs) developed for military aircraft in the 1950s.

Commercial adoption for maritime use began in 1979, although early devices relied on aircraft detection and could take hours to locate.

The shift to 406 MHz satellite detection in the 1980s and 1990s dramatically improved global coverage.

In the 2000s, PLBs incorporated GPS technology, improving position accuracy to within 100 meters.

Modern devices such as the ACR ResQLink AIS and Ocean Signal PLB3 combine satellite distress signals with AIS and return-link technology for faster rescues.

Satellite Communication Devices

Two popular satellite communication systems for sailors are:

• Garmin inReach

• Iridium GO!

Both use the Iridium satellite constellation, providing global coverage far beyond cellular networks.

Garmin inReach

• Text and email messaging

• Location tracking

• Emergency SOS alerts

• Rugged, handheld design

Iridium GO!

• Functions as a WiFi hotspot

• Supports voice calls, emails, and data

• Can download weather GRIB files

Starlink for Marine Internet

In some ways these systems are now complemented by Starlink marine internet, which provides high-speed satellite data connections worldwide.

Starlink uses thousands of low-Earth-orbit satellites, delivering speeds up to 500 Mbps.

Although it is not designed specifically as an emergency system, it enables voice calls and high-bandwidth communication at sea.

However, marine plans can be expensive, and Starlink charges higher rates when operating offshore.

Summary: Which Marine Emergency Electronics Should You Carry?

Each system serves a different safety purpose:

• EPIRB – Emergency beacon registered to the vessel

• PLB – Personal safety beacon registered to an individual

• Garmin inReach / Iridium GO! – Two-way satellite communication

• Starlink – High-speed internet offshore - great for weather

• VHF radio – Essential short-range marine emergency communication

Assuming you already have a VHF radio with AIS, the satellite communicator is a good low cost addition; if you can afford it, take all of them - what price is safety?

Ready to become a safer, more confident sailor? Explore our sailing courses and hands-on training opportunities at Satori Sailing.