AIS Basics: Automatic Identification System, Explained

What is AIS exactly, and why should boaters care?

22nd July 2012.
By Lenny Rudow

If you haven’t heard about AIS (Automatic Identification System) yet, you’ve been missing out on one of the really useful technological gems to have emerged for boaters in recent years. The system is now mandated in large commercial cargo and passenger ships, and while it isn’t required for a recreational boater to have AIS onboard, knowing where all of those ships are going can be an extremely helpful collision-avoidance tool.

Want to give yourself a safety boost the next time you set out across the bay? Then consider adding AIS. With electronic nav gear like this on board, there’s no doubt you’ll be a better-informed boater.

So, how does AIS work? Ships are fitted with a transponder, which broadcasts a wide range of information via VHF frequencies (161.975 MHz and 162.025 MHz). This info includes data about the ship itself, such as the MMSI number, its name, size, type, cargo, and draft. It also includes data about the ship’s movements, including speed, destination, ETA, and COG. This info is available to anyone who has an AIS receiver, and can also be tapped by accessing the Internet on websites like Liveships.

AIS transponders come in two flavors: Class A, and Class B. Class A units are more powerful (12 watts) and include a display, while Class B units are weaker (two watts) and don’t necessarily have a display screen. What’s far more interesting to the average recreational boater, however, is an AIS receiver. Without broadcasting any information about your own boat, a receiver will let you see all of the AIS-equipped ships around you. Many receivers have collision alarm settings, or warn you of ships that are travelling in a direction and speed such that they have the potential to become a collision problem.

Having all of this AIS info is great, but as you might imagine, in a crowded harbor or shipping lane it can create a data overload. Many systems project this data right onto your chartplotter screen, which can cause a confusing swarm of targets to appear and make navigation nearly impossible. That’s why most serious mariners prefer a stand-alone dedicated AIS unit with its own screen. This increases cost significantly—adding AIS to an existing NMEA 0183 system can be done for as little as a few hundred dollars, while stand-alone units can cost thousands—but in most cases will be well worth the added expense. And some of the latest and more advanced systems, like the Vesper Marine Watchmate Vision—which won the 2012 NMMA Innovation award for Safety and was a Boats.com 2012 Top New Electronics Pick— can be programmed to clear the screen of vessels that don’t present a collision threat. (FCC approval is pending, so pricing for the Watchmate Vision hasn’t been set yet, but the original Watchmate retails at just over $1,000).

The latest in dedicated AIS units, like this Watchmate Vision from Vesper Marine, can filter out unwanted targets.

If you only need the AIS basics and you boat in waters close to populated areas, you can even access AIS by smartphone. One new app, called Boat Beacon, brings the data up right on your phone. The app provides collision detection out to 60 miles, CPA calculations, basic GPS data, and MMSI numbers so you can hail nearby vessels directly. Boat Beacon is available for iPhones only, and it goes for $9.99 on the iTunes store.

AIS technology has also proven helpful in ways no one expected, as well. Again, the purpose is safety. Just this past spring, Kannad Marine introduced the Safelink R10 SRS, a personal AIS—or PAIS—which takes advantage of AIS for personal search and rescue. This unit clips onto a life jacket, and once activated, it broadcasts your exact GPS position. You’ll then appear on the AIS screen on any vessel within its range of about four miles. Kannad also makes an AIS equipped SART (search and rescue transponder).

- Lenny Rudow


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About the author:

Lenny Rudow

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Lenny Rudow is Senior Editor for Dominion Marine Media, including boats.com and YachtWorld.com. With over two decades of experience in marine journalism, he has contributed to publications including Boating Magazine, Marlin Magazine, Boating World, Saltwater Sportsman, Texas Fish & Game, and many others. Lenny is a graduate of the Westlawn School of Yacht Design, and he has won numerous BWI and OWAA writing awards.
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