Zanshin I EPIRB (Emergency Position Indicating Radio Beacon)

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<em>Zanshin I</em>'s EPIRB The EPIRB (Emergency Position Indicating Radio Beacon) above the navigation station on Zanshin I, next to the mandatory ship plaque (well, mandatory for U.K. registered vessels).
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Zanshin I's EPIRB

In recent years modern electronics and satellite systems have gone a long way towards making offshore sailing (and motoring as well as flying) a lot safer. GPS has become so ubiquitous that many cell phones have built in receivers and it is hard for us to imagine that, until very recently, it was very difficult to know where on the earth one was.

The use of magnetism in compasses stretches back a long way, the Chinese knew of them as far back as 200 B.C. and they were in common use in vessels from the 11th century A.D. Europeans adopted the dry compass for navigation around the 14th century. But a compass alone doesn't tell you where you are, it just tells you in which direction the magnetic north pole is.

Celestial navigation is the art of using heavenly objects to determine location. Determination of one's latitude (how far north or south of the equator one is) was achieved quite early, but being able to accurately determine one's Longitude was impossible until the late 18th century! And now we know, to within a couple of feet, exactly where we are on the earth's surface using just our phone or a hand-held GPS device. Plus, if the satellite coverage is good, we can also get a pretty accurate altitude reading.

EPIRB Registration document EPIRB Registration document
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EPIRB Registration document

Back to safety. Before the advent of GPS a sinking ship would have to radio their position and status using a MAYDAY call, hoping that someone is within range and listening to their radio on the right frequency. Since boats tend to sink less often in good weather and calm conditions, it was difficult to give an accurate position. Getting an accurate fix mean using a sextant to measure the angle between the horizon and a celestial object such as the sun, moon or a known star as well as the exact time of the measurement. With this information one could consult a thick almanac full of tables to determine a positional fix, but this is hard to do when you cannot see the horizon or any stars during a storm or when the boat is sinking away from underneath you. How much simpler it is to read your Latitude and Longitude from a GPS, or better yet to have it transmitted automatically with your emergency signal.

The GMDSS system is an international set of systems that optimize the notification and rescue of people in ships at sea. There are several important and interconnected components to the system but I will just touch upon the EPIRB. This beacon is registered to a single vessel by whatever national authority is responsible for the country of the boat's registry. When activated in an emergency, it transmits the distress signal, the EPIRB's unique identifier and the GPS coordinates of the device on 406MHz. This signal is picked up by various satellite systems and then forwarded to the nearest SAR authority. Since 97% of all beacon alerts are false alarms, the SAR (Search-and-Rescue) authority will usually use the registration details to call the contact number and thereby cross-check if the vessel is actually in use. EPIRBs will also broadcast on the old emergency frequency of 121.5 MHz, but this functionality is slowly being phased out.

While an EPIRB is a way of notifying authorities that a vessel is in trouble, it doesn't mean much if you are 2000 miles away from land in the south Pacific ocean; on land a 911 call will be acted upon promptly and you can assume that medical or other assistance will be dispatched quickly. At sea the authorities will do what they can, but chances remain very high that it will take days for some ship to be diverted to your EPIRBs coordinates to check. If you are drifting in a life raft with your EPIRB then chances are that you will be found; but at least someone, somewhere will know that something has gone awry when the EPIRB goes off and alternate communication ceases.

Downloadable Manuals page - EPIRB Manuals

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