Skip to main content

AIS: the electronic eyes of navigation

The collision avoidance tool allows vessels to ‘see’ each other in all conditions, among other functions

AIS is especially useful at night or in fog, providing a snapshot of vessel traffic and such information as position, course and speed.

AIS is perhaps one of the most significant developments in navigation safety since the introduction of radar, depth sounders and GPS. Mandated aboard most commercial vessels since November 2003, AIS is now readily available for recreational boaters.

AIS, which stands for Automatic Identification System, is a standardized navigation safety system originally developed as a collision avoidance tool to enable commercial vessels to electronically “see” each other in all conditions and improve the helmsman’s information about the surrounding environment. AIS data can be overlaid on radar and chart plotters, providing a combined view and critical safety data with its ability to “see around corners,” where radar may have limited functionality.

The first steps in collision avoidance are seeing and being seen. This is where AIS comes into play. For vessels equipped with the system, AIS provides such information as vessel position, course, speed and navigational status (under way, at anchor, etc.), as well as its name and type (sail, power, tug, ferry, etc.). The system continuously transmits this information to all other AIS-equipped vessels within range.

A vessel with AIS also receives this information from other AIS-equipped stations, providing it to the skipper in a number of different ways. The data can be viewed on stand-alone displays that provide “text only” listings, or it can be integrated with chart plotters, radar displays and computerized navigational software run on a PC.

Class B AIS, such as ACR's Nauticast B, both transmits and receives vessel data.

Chuck Hawley, a longtime sailor with some 40,000 miles under sail, is vice president of product development for West Marine. We discussed AIS, where it is today, and how it fits into the recreational boater’s navigation and safety package.

Earlier this year, Hawley hosted a series of seminars at the Oakland (Calif.) Boat Show and found that most of the attendees had come to find out about AIS, which West Marine sells. “With the changes in technology, about 20 percent of the people that I spoke with truly understood AIS,” says Hawley. “We’re moving from Class C receive-only into true AIS Class B transmit and receive, where you show up on somebody else’s vessel display screen. AIS is real and, therefore, easy to understand. You can look at a display, then look at the area and see the same things.

“Small vessels in limited visibility or on night passages with commercial vessels in waters will find AIS extraordinarily useful,” he adds. “On the open ocean or foggy runs, AIS provides a great defensive aid, because you can see large vessels around you.” Class B AIS is a powerful navigation tool, and the information it receives from other AIS-equipped vessels, especially when combined with radar, provides a range of benefits not limited to collision avoidance. AIS also facilitates clear bridge-to-bridge communications on VHF radio. And friends and family can locate an AIS-equipped boat simply by using a computer with an Internet connection.

Although AIS data can be displayed on radar screens, Hawley says it’s easier to interpret than radar. “AIS is involved at the simplest point; radar is never easy,” says Hawley. “When an AIS vessel transmits its location, there is no wondering what the blip on the radar screen might be. All the data you need is right there.”

The Web site tracks AIS-equipped vessels in ports around the world.

In researching AIS, I corresponded with Capt. Robert Forbes, who has more than 50 years of sailing experience. Forbes and his wife equipped their 46-foot sloop with an ACR Nauticast Class B AIS in early 2008 for a passage from Mexico to the South Pacific and through French Polynesia and the Cook Islands.

“Given the low cost of current Class B systems, no offshore boat should be without one, particularly near commercial shipping lanes and harbors,” says Forbes.

Forbes documented several close encounters with container ships and other commercial traffic while cruising to the Marquesas, but we can experience similar issues just crossing Long Island Sound. “Having lived with our unit across the Pacific for over a year, I consider Class B AIS to be lifesaving equipment,” he says.

Forbes has a background in aviation and says that Class B AIS is “simply the long-awaited, low-cost marine equivalent to the air traffic radio transponders legally required in all aircraft operating over and between major cities throughout the world.”

Capt. Marty Golden is employed by Reinauer Transportation as captain of the 4,000-hp ATB (articulated tug/barge) Ruth Reinauer, based out of New York Harbor. With an LOA of 116 feet, a beam of 35 feet, draft of 16 feet and weighing 743 tons, this is one vessel you’ll want to keep track of if you’re cruising in the area.

Following his 1981 graduation from Massachusetts Maritime Academy, Golden sailed both ocean and harbor tugs and held an 11-year position aboard the 100-foot hawser boat Jill Reinauer. As captain of the Ruth Reinauer, Golden works with a Furuno FA150 Class A AIS interfaced with two Furuno FAR2117 radars with 20-inch LCDs. He says AIS is the best invention he has seen as a professional mariner, but adds that it can be a double-edged sword.

Golden believes regulations should limit both commercial and recreational vessels under a certain tonnage to having receive-only Class C AIS. His concern stems from working in areas that can be crowded with recreational boats. “If everyone has Class A or B AIS, it would be very difficult to quickly sort through the displayed data,” he says. “Another variant on that could be to provide selective layers or filtering options for the received data.”

Locate New York Harbor at, and you’ll begin to understand Golden’s thoughts regarding filtering and limits. There were 180 AIS targets in the harbor when I recently visited the site.

AIS is growing in popularity as more boaters experience it and understand it. “There is a stable price point right now of $500 to $1,000, although there may eventually be some deterioration,” says Hawley.

He says installation is relatively simple and can be done by someone with average skills. “With AIS there are no concerns about weight aloft, power consumption or windage, as there would be with a radar installation,” he says.

I have found Class B AIS transponders starting at $399 and priced as high as $3,500. I recommend searching the Web for “AIS transponders” and spending some time reviewing the options. I’ll address installation, setup and accessories in a future Tech Talk.

My West Marine AIS-1000 has a “silent” button that allows the unit to receive, but not transmit. There is no reason that the tug captain pulling a barge in Long Island Sound needs to know that I’m motoring around West Neck Harbor.

Although AIS technology and the regulations regarding its use are still evolving, I believe the system will be a valuable adjunct on many recreational boats. It’s relatively easy to install, requires no real “operation,” and provides important navigation information. Of course, like all of the tools at our disposal, it needs to be understood and used sensibly to be of value.

Frank Kehr is a technical writer for Soundings.

See related articles:

- The carriage regulations for AIS

- Breaking down the ABCs of AIS

This article originally appeared in the August 2009 issue.