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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.

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.

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

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

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

“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.

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.