AIS is an acronym for the shipboard Automatic Identification System, an autonomous VHF radio linked vessel position reporting transponder system. The Maritime Transportation Security Act of 2002 requires many commercial vessels to be equipped with AIS. At present there is no requirement for AIS on any U.S. recreational vessel, unless perhaps your yacht is the size of an ocean going ship (and there are some of those around). However, the benefits of installing part of the AIS system is spurring the sale of AIS receivers to recreational boaters.

AIS is a transponder, or a device that automatically receives and transmits information. The reporting function of an AIS is similar to the radar transponders used in almost all aircraft, where it tells air traffic control who you are, where you are and where you are going at that moment. Signals from a vessel's AIS transmitter can be heard by any other AIS system (or any AIS receiver) in VHF radio range. The information sent includes: the vessel?Ĵs position; course; speed; name and Maritime Mobile Service Identity (MMSI) number; length; beam; draft; classification (type of vessel); maneuvering information (underway / at anchor); destination, and whether the vessel is carrying hazardous cargo. (Don't worry too much margarita mix doesn't qualify as hazardous material.) In short, it provides more information than you, the recreational mariner, will likely require.

A complete AIS system costs somewhere between $4,000 and $8,000, plus the cost of installation (which includes the two required VHF antennas). Many large yachts are voluntarily equipped with AIS and enjoy the advantage of being full participants in the system, ensuring that all AIS equipped vessels in range will know what the yacht is up to. However, there can be overwhelming value in knowing what the other guy is doing, even if you don't tell him where you are and what you are doing. Install an AIS receiver / display system on your boat and you will have access to virtually all of the benefits of AIS, at a fraction of the cost of a full transponder system. Not informing the other vessel of your position and movement is not as un-seaman like as it may sound. A large ship won't likely be able to alter his course and speed to avoid a close passage situation, its up to you to stand clear.

The AIS signal is broadcast on VHF radio channels 87B and 88B, therefore existing marine receiver technology can be used without alteration. The decoding is done with a specially programmed chip set. A "blind" receiver that provides a NMEA 0183 output can be purchased for as little as $200. A wide number of chart plotters and radars are able to accept the data stream from the AIS receiver and will display the information transmitted from any AIS equipped ship in VHF range. The details of the data display vary somewhat depending on the specific chart plotter or radar being used.

How would AIS effect your day on the water? Well, a large ship converging on your port bow would know who you are and would likely have called you on your VHF/DSC radio, warning you to stand clear. (Don't ever assume that anyone larger than you will give way, especially ships constrained by their draft, a common occurrence in most harbors.) However, your AIS receiver provides you with the other vessel's MMSI and name. Entering his MMSI into your VHF/DSC radio and pressing the "enter" or "send" key will immediately establish communication. His response to your call won't depend on the setting of the volume control on his VHF set. Your DSC call to his MMSI will be clearly and loudly announced by his radio, which will automatically switch to the working channel you have selected. The result is low pucker-factor voyaging, especially in crowded waters. And to me, the less pucker, the better.

The value of the AIS data extends well beyond the last minute call to a close-by vessel. Depending on the software in the AIS display system it may be able to predict possible close encounters with AIS reporting vessels, showing the distance, location and time of the closest approach. In other words, the system is anticipating possible problems.

The advantage provided by an AIS receiver is especially dramatic when used in conjunction with radar. The converging radar target two miles off your starboard bow is now positively identified as an AIS target. You know his name, MMSI, course, speed, size, type of vessel and based on the prediction made by the system's software that it will safely pass at a distance no closer than a half mile, (provided both vessels hold their current course and speed).

Until recently it was possible to view almost real-time AIS reports from ships in many of the world's ports by logging on to www.AISlive.com. However, the content of the "public" portion of the web site has been restricted due to "security" concerns. This seems odd since subscribers can apparently access this almost real-time data. We doubt that anyone with malicious intent would be deterred by having to pay a modest annual subscription fee. For a complete listing of companies who offer AIS equipment, log onto www.boatdigest.com.