Will AIS help ships avoid sailboats?

One of the biggest issues that any sailboat driver has to face is keeping an eye out for other traffic, especially big ships, to avoid collisions. Now a new program called the automatic identification system (AIS) is emerging that should substantially improve the ability of sailboats both to be seen by ships and to keep track of ship movements.

According to International Maritime Organization (IMO) rules under the SOLAS convention, AIS will be required on merchant vessels of more than 300 gross tons built after July 1, 2002. AIS will be phased in year by year until 2008 when most commercial vessels large and small will be required to have them aboard. Eventually, vessels of all kinds, including voyaging sailboats, will presumably have AIS packages on board.

GPS, of course, tells you where you are. It also allows other vessels in your area to calculate their positions. Since everyone already knows their position, what if there was a way to automatically communicate positions to each other? An automatic system that shared information among vessels would allow all ships and boats in a given area to know the position of every other vessel in the vicinity. And more than position could be displayed; each vessel could also display its name, course, speed, heading, vessel type, cargo on board, and more. The information for each vessel could then be displayed on an electronic chart plotter or a radar screen, or on an electronic chart running on a laptop. In addition to knowing a great deal about other vessels, such a system would have the capability to display short text messages sent from one vessel to another or to all vessels in the surrounding area.

This type of AIS setup links vessels into a local area network, providing a great deal of useful information to each vessel about the boats and ships surrounding it. At first glance, this system might seem to be merely replicating the ability of radar, especially radar equipped with an automatic radar plotting aid (ARPA), to display the situation around a vessel. In its fullest implications, however, AIS offers a great deal more capability than an ARPA. For professional mariners, who often operate large, heavy vessels at high speeds, any extra knowledge about other large vessels is certainly welcome. Not only that, but a stream of GPS position data from another vessel can be used to calculate a raft of information about another vessel, such as rate of turn, leeway, whether the vessel is accelerating, or decelerating, etc. And while radar does provide collision avoidance information, the quality of the radar data is dependent on the quality of the radar set, whether it’s in tune, and whether it is being interpreted by a properly trained operator. The information on other vessels provided by an AIS setup is standardized, every vessel with AIS-capable equipment will send and receive the same data.

Not only can vessels all share the same information, but shore stations, like a Coast Guard vessel traffic service (VTS) office, will be able to use AIS information to track all the vessels in an area. The Coast Guard’s previous VTS efforts were radar based. This meant that multiple radar sites had to be set up to provide complete radar coverage for a harbor. It also meant that only the VTS watchstanders could see the complete situation of vessels in a harbor. With an AIS-based VTS, the officers and pilot on each ship know as much about the traffic situation as the VTS crew. This reinforces the traditional independence (and responsibility) of each vessel’s captain to navigate his or her vessel safely.

GPS or DGPS is the position-finding anchor of this system, although other nav aids can be used if desired. But AIS doesn’t work unless there is a way for each vessel to automatically communicate its position and other nav data to other vessels in the vicinity. This is where VHF DSC radio comes in. AIS units have one channel designated for transmitting and three for receiving. All AIS data transfer takes place on these frequencies. But what about busy harbors? How can a few channels handle the message traffic for all the vessels typically found in a harbor like New York or Rotterdam, for example?

The developers of AIS have devised a clever communications protocol for AIS that allows multiple radios to use the system without a central control station. The protocol allows stations to cooperatively work out time slots for sending and receiving AIS data. The software that runs this cooperative networking is reportedly very robust. “It can handle tremendous capacity,” said Joe Hersey, chief of spectrum management for the Coast Guard. “We have a simulator for testing [AIS equipment] and we’ve found you can’t overload it.”

Without the need for a central control station, an AIS-equipped vessel can automatically become part of local wireless networks as it travels along a busy coast. As it comes within range of other vessels, it will become part of that local group. When a vessel moves out of range, it drops out of the local network and joins another one as it encounters new vessels. The AIS setup is inherently local and uses the line-of-sight nature of VHF signals to be self-limiting.

The IMO requirement for ships to carry AIS gear is also a benefit for coastal nations. AIS-equipped shore stations can automatically obtain information about ships and cargoes as they transit coastal waters. This information can aid rescue forces in an emergency. And SAR aircraft may carry their own AIS packages so they can be visible to vessels engaged in surface search. There is also discussion of a AIS units that can be placed on nav aids like buoys or daymarks to make them actively visible to mariners. The one downside to AIS is compliance. “Everyone needs to carry it,” said Hersey. “Otherwise, they’re invisible.”

Clearly, the advantage of AIS to shipping and to coast guards around the world is substantial. But this technology may ultimately benefit sailors even more. After all, one of the biggest worries of the average sailing voyager is that large, fast-moving ships pay no attention to small vessels like sailboats. And this fear that merchant ship officers are not paying particularly close attention to sailboats is reinforced by experience and by evidence like Don Dykstra’s recent article written from the point of view of the ship’s watch officer (“A view from the bridge,” Issue No. 110, Nov./Dec. 2000). In his piece, Dykstra outlines some of the reasons why a watch officer on the bridge of a ship may not see your boat and why, even if he does, he may not be able to do much about it. The theme of Dykstra’s piece is chillingly simple: “Since you can’t expect a ship to pick you up visually or on radar, you’d better stay out of the way.”

AIS technology has the potential to change the sometimes deadly interaction between ships and sailboats. Several manufacturers, such as Ross Engineering in Largo, Fla., have expressed interest in producing a modified AIS package, called a class B unit, for use on smaller vessels like sailboats. A sailboat equipped with an AIS setup suddenly is an equal to every ship surrounding it. By exchanging position data with ships, a sailboat is visible on the electronic chart displays of every ship within range. Sailors no longer will have to worry about whether their radar reflector is on the “catch rain” position, and whether they are showing up on an approaching ship’s radar screen. AIS acts as a sort of smart radar. Ships know there is a sailboat nearby (provided someone on the bridge is actually looking at the electronic chart screen), and more important, the sailors know the position, course, speed, etc., of all the ships in VHF range. Thus, AIS gives sailors a powerful tool to help be seen by ships and to aid both parties in collision avoidance.

“It’s even better than a radar,” said Larry Simpson, sales manager at Ross Engineering. “When do you need a radar? When there’s a storm and radar doesn’t work very well. This system works even in a storm.” VHF signals are not affected by heavy rain like microwave radar signals.

How soon will AIS gear be available for use on sailboats? According to Simpson, Ross has plans to produce a class B AIS unit. “We’re going to do it,” said Simpson. According to company president Ross Norsworthy, class A and class B units will both be available by the fourth quarter of this year. However, since the FCC hasn’t set up rules for type acceptance, there is question about whether these units will be on sale by then.

By Ocean Navigator