Collision avoidance is as important to recreational sailors as it is to the commercial mariner. Both groups therefore benefit from the international effort to implement the Automated Identification System (AIS). Initially mandated by the International Maritime Organization (IMO) for vessels over 300 tons, AIS Class A has spawned a second generation of transceivers (Class B) that serves the needs of the small-craft community.
The system ties together a two-channel VHF communication capability, GPS data and registration information to create a digital location/identification signal that is broadcast to all similarly equipped vessels and stations. The electronic line-of-sight range is a nominal 20 miles in open water, and often quite a bit more. Vessels in the same locale automatically comprise a virtual network, advising each other continually of their location, identity, course and speed.
Class-A transceivers used on commercial vessels are more powerful (12 watts) and employ a more frequently updated and more detailed data stream than the Class-B units (2 watts) used on recreational vessels. The more capable Class-B units have twin receivers and respond to the alternating-channel AIS signals much more quickly. Many of the latest products have alarms that sound when a collision course with another vessel is perceived, or when a vessel has entered a pre-set guard zone.
Some systems allow AIS data to be sent to remote multifunction displays (MFDs) around the boat; others are stand-alone units with independent antennas. AIS data can be displayed as text, as blips on an independent LCD screen, or as an overlay on a digital chart and/or radar display. Stand-alone advocates prefer to see AIS signals displayed separately, and the same rationale goes for their radar and chart displays. The choice is a matter of personal preference, and either approach is valid.
Many sailors who are more suspicious of technology opt for receive-only AIS, a one-way approach to data-handling that does not communicate your position to others. Like Class-B transceivers, a receive-only unit can be used as a stand-alone aid or can be networked with other electronics. These receive-only terminals may not be the complete answer when it comes to collision avoidance, but they are a big step in the right direction. Having information on who to avoid is more than half the battle, and an AIS transponder can always be added later.
A tool, but not a panacea
There are some issues all users should be aware of. First, just because you see a large merchant vessel on your AIS display, doesn’t mean its crew can see your AIS signal. Newer Class-A units do detect and display Class-B signals, but most older units, many of which are still in service, cannot. Merchant ships also may find inshore waters so cluttered with AIS signals that they may intentionally filter out Class-B data.
As charting software becomes ever more sophisticated, there’s been an increased ability to analyze AIS vessel movement. Screen display size and contact clutter can, however, impact user friendliness. In traffic-congested areas where there’s room on a screen to display only the most threatening contacts, bear in mind that an abrupt change in your course will instantly shuffle the deck and can easily present a whole new set of closing contacts to evaluate and keep track of.
Remember, too, that constant bearing decreasing range (CBDR) relationships with other vessels are often just as easily seen on radar. The combined use of AIS and radar is, in fact, a very powerful way to double-check your collision avoidance. Vessels, buoys and all types of other obstructions that don’t broadcast AIS signals usually show up just fine on radar. Radar is also self-contained and does not rely on satellite transmissions or equipment aboard other vessels.
Finally, it’s important never to lose sight of the fact that visual navigation rules are in play most of the time. Watching LCD screens should never be an alternative to keeping a good lookout.
Dancing with Big Brother
Though initially billed as a collision-avoidance aid, the ultimate role of AIS will likely be more multifaceted. The U.S. Coast Guard is now implementing a Nationwide Automatic Identification System (NAIS), a universal vessel-tracking system that eventually will incorporate a satellite array that can detect AIS signals from up to 2,000 miles away. Closer to home, the system will process data from a necklace of sea buoys on the coastline and from shoreside Rescue 21 towers. All this data will be integrated to give the government a “big picture” on vessel movement.
NAIS Phase I is already in play and tower tracking in one sector on the lower Chesapeake Bay is up and running. The stated purpose of the program, according to the Coast Guard, is “vessel-tracking correlation, intelligence processing and anomaly detection.” The Department of Homeland Security, meanwhile, describes the NAIS program as one that “will complement other surveillance and intelligence systems in identifying vessels requiring further investigation and action.”
One obvious upside of this “we always know where you are” system will be expedited responses to calls for help. With increased use of AIS, as well as DSC-VHF radios, less and less precious time will be spent trying to divine the identity and locations of vessels in distress. But there are downsides, too. Already there are advisories about shutting off AIS transponders in waters where pirate activity is an issue. And several queries have been raised about the legality of selling the tracking information garnered by the system.
Right now recreational boaters can still choose how much they want to track others and whether they want to be tracked. AIS capability is mandatory for larger commercial craft and for fast motor vessels over 65 feet, but is still entirely optional for the small-craft community. Whatever else it’s used for, AIS is obviously a very legitimate collision-avoidance tool and is priced to sell. However, some may have concerns about its eventually becoming an extremely effective means of surveillance.
Sailing has always been a soft footprint activity, affording sailors a chance to truly taste freedom and get away from it all. Right now AIS is perceived as a non-intrusive safety asset, but the time may come when we are required to switch it on before leaving the dock. Many, of course, would rather not see that happen. As with all promising technology, it will be how the system is used that tells the final story.