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What is an EPIRB and how does it work?
Well, let’s start with what it stands for, EPIRB stands for Emergency Position Indicating Radio Beacon. It’s an emergency radio beacon that typically transmits a signal on a radio frequency of 406MHz when it’s activated. They’re commonly carried by sailors and mariners as a means of calling for help and indicating their location to rescue services in an emergency. Should you carry one on your boat? And how do they work? Let’s find out.
Here’s an example of a larger EPIRB, more modern devices have become more compact.
So how do EPIRBS really function? Let’s keep it simple and follow the chain of events:
Your sailing yacht strikes a shipping container in the Bay of Biscay and begins to sink. You activate your EPIRB.
The EPIRB starts sending out a radio signal on a frequency of 406MHz. This radio signal is picked up by a set of satellites that are part of the COSPAS – SARSAT system (an international program for managing satellite-based search and rescue).
The satellites essentially send on the signal to a ground based station known as a LUT (Local User Terminal). This is typically a government owned dish antennae.
The LUT processes the signal using powerful computers and sends it on to a MCC (Mission Control Centre). The MCC is basically a centre with people that route the information to two places:
1. The closest Search and Rescue authorities to your location.
2. The authorities of the country of origin of the EPIRB (typically where it was registered or bought).
The Search and Rescue authorities then have information on your location and can begin their rescue efforts.
If your EPIRB is registered then they’ll also be able to access additional information like your vessel type, name and the emergency supplies you have. They do this by searching the Beacon registration databases. This is why it’s really important that you register your EPIRB correctly. The website https://www.406registration.com/ allows you to register your EPIRB (Site managed by COSPAS-SARSAT).
Many EPIRBs also transmit an additional weaker signal on a frequency of 121.5 MHz to help rescue services home into the device’s location when they are nearby.
A French rescue helicopter uses the information to find you and rescues you and your crew from the Bay of Biscay. On the flight back to shore you make a mental note to leave a good review for your EPIRB.
So there’s the basic overview of what happens when you activate your EPIRB. Now we’ll have a quick look at the more technical side of how it works, feel free to skip past this section if you aren’t interested in this aspect.
The Satellites used by EPIRBs
So we mentioned already that the program managing satellite-based search and rescue is called COSPAS-SARSAT. This program uses two sets of satellites to receive the distress radio signals from EPIRBS.
LEOSAR is a set of low altitude satellites orbiting around the earth whereas GEOSAR is a set of geostationary satellites (basically they stay in one position). There’s also a new set called MEOSAR (Medium altitude orbiting satellites) being introduced that will improve the system’s effectiveness.
The thing is there may not be a satellite in the right position to receive your distress signal right away. At mid-latitudes the typical waiting time is less than an hour (Source: COSPAS-SARSAT). At higher latitudes it could take longer than this before a satellite is in a position where it can receive your signal. Then once the satellite receives your signal it stores it in a memory module until it’s in sight of a LUT. At this point it broadcasts your signal on to the LUT.
This is known as ‘global mode’ and it’s the reason why EPIRBs are able to function around the world even when hundreds of miles from land.
How do EPIRBs find your location?
There’s two types of EPIRBS; standard and GPS-Enabled. GPS enabled EPIRBs cost about 50% more but they transmit your GPS location along with the distress signal. This allows for location to be determined to within about half a nautical mile. It also means that your location can be determined quickly (about 3-5 minutes). Check out this article by Boat US Foundation for in depth info on GPS EPIRBs.
Now for the standard EPIRBs, here’s how they find your location:
Imagine you’re standing on the street and an ambulance speeds by you. Listen to the noise of the siren as it passes. The pitch of the sound from the siren changes as the ambulance’s position relative to where you’re standing changes. If you haven’t noticed this before, watch out for it next time an ambulance passes you by.
This is known as the Doppler Effect and basically it says that the frequency of sound, light or other sources changes as the source or receiver move relative to each other.
So now we’re back on our sinking yacht in the Bay of Biscay and our EPIRB is sending out a distress radio signal. Overhead, one of the satellites in the LEOSAR set is speeding around on it’s orbit of earth. Imagine the satellite is ‘listening’ for your signal. As the satellite speeds past; just like the ambulance did, the frequency ( ‘sound’ ) of your signal changes. Then, since the exact location of the satellite is known, it can calculate the position of your sinking yacht based on the changes in frequency of your signal caused by the Doppler Effect. They use a complex mathematical equation to calculate this but we don’t need to know it.
So that’s how the satellites find the location of your EPIRB when you send a distress signal! Then the location is passed on to the LUT and eventually reaches the search and rescue authorities so they can find you and rescue you.
How to use an EPIRB
Note: Consult your product manual when you buy your EPIRB, or if you already own one, do a google search for your model’s product manual. This is the best place to find specific instructions for your EPIRB.
There is typically two ways to activate an EPIRB:
- Automatic activation, many modern EPIRBS will activate automatically on contact with water and begin sending their distress signal.
- Manual activation, the process is different for varying EPIRB models but the typical process involves opening a safety covering and then holding down a button for a period of seconds.
There are two categories of mounts for EPIRBS, CAT I and CAT II.
CAT I mounts release the EPIRB automatically when it is 4-13 feet underwater. It’s important that the mount is placed somewhere that the EPIRB can float free and not be trapped in the event of sinking or inverting.
CAT II simply holds the EPIRB until it is taken out of the mount manually.
It’s important to mount the EPIRB somewhere that it’s not as risk of being caught in a fire or being bumped with doors or used as a handle.
Here’s a good article from the US Coastguard on mounting your EPIRB.
What is the range and battery life of an EPIRB?
Note: Refer to your EPIRB’s product manual or specifications sheet for exact information, if you are purchasing an EPIRB, this information will be available from the manufacturer.
The battery life for a stored EPIRB should be in the range of 4-10 years. There should be a battery expiration date on your EPIRB when you buy it. After that date you’ll need to get the battery replaced professionally.
When transmitting a distress signal, the minimum battery life is 24 hours but some models may transmit for up to 48 hours.
In terms of range, let’s look at two aspects:
Where can the EPIRB distress signal be picked up?
It can be picked up globally thanks to the fact that a passing satellite can store the information about your signal until it comes into sight of a LUT (Ground station). This means that even in the middle of an ocean, your distress signal can be passed onto a ground station and onwards to search and rescue authorities.
How accurate is the location that the EPIRB indicates in the distress signal?
For GPS enabled EPIRBs it can be as accurate as 100 metres. For standard EPIRBs it should be around 3-4 nautical miles.
What is the difference between EPIRB and SART?
Let’s start with what SART stands for; Search and Rescue Transponder. So how does it differ from an EPIRB?
Well an EPIRB is an emergency radio beacon, it transmits a radio signal to communicate it’s distress message. A SART is a small, battery powered device that when turned on, creates a distinctive series of 12 blips on the radar screens of ships or aircraft that come into range of the device. It is only able to do this when it is ‘interrogated’ by a radar system.
They’re typically used on liferafts of large ships but could be useful on a distressed sailing vessel also. A ship will typically be close enough to see the device on their radar at about 8km away while an aircraft will see it at about 48km away. Source: The Complete Sailing Manual, Steve Slight.
There’s also a new variety of SART called an AIS SART. AIS (Automatic Identification System) is a global system for tracking ships and smaller vessels that voluntarily carry it. These types of SARTs are GPS enabled and transmit their location on AIS which allows for their location to be more easily determined.
Should you get an EPIRB for your boat?
Short answer: If you sail outside of VHF range, it’s essential. If you sail within VHF range it’s optional but still recommended.
The major advantage of EPIRBs over other methods of calling for help is that they have global coverage. You don’t need to be within range of a VHF tower or depend on someone spotting your flare.
Even if you normally sail close enough to the coast to be within VHF range, if you were to have a dismasting or an electrical failure your VHF would suddenly be out of the picture. Also, because VHF is a ‘line of sight’ technology, there’s a good chance you could sail in places where no tower or vessel is within a line of sight to hear your VHF mayday call.
The RYA say “Put quite simply an EPIRB could mean the difference between surviving an incident at sea and losing your life”.
If the cost is a barrier then you could consider hiring an EPIRB just for your extended trips further from shore. Here’s a UK based EPIRB rental and a US based EPIRB rental. In another country? Try googling “EPIRB rental + “your country” and see if there’s any options near you.
Relate Read: The 4 Best Flexible Solar Panels for Boats
What price is an EPIRB?
They range in price from about €350 (£315/$420) – €800 (£720/$920) for a brand new unit. It’s not a small sum of money but for the safety net they provide, I personally consider it to be an entirely worthwhile investment.
If you purchase an EPIRB second hand, make sure to update the information registered for the EPIRB so that in the event of an emergency, the correct info is available for rescue services. This is critically important as otherwise they could be looking for a boat that looks completely different to yours. Here’s a guide on changing ownership of EPIRBS.
Conclusion
Well, hopefully that addressed all your questions on EPIRBs. You should now understand the basics of how they work and why it’s a great idea to carry one onboard. If you choose to buy one remember to: a. Register it! and b. Read the product manual, the information here is just a guideline, for the most up to date information consult your product manual or ask the manufacturer / supplier of your EPIRB.
If you’ve any questions on EPIRBs or any suggestions for improving this article, please leave a comment below! Best of luck on your voyages and safe sailing.