IT'S NOT EVERY DAY THAT YOU SEE A SHIP HOVERING ABOVE THE SEA. Of course, it's also not every day that you find yourself sailing from Ketchikan, Alaska, to Seattle under warm and sunny solstice skies-but there I was. And there was the gravity-defying ship.Just as I began to question my watch-standing skills, Erden, my friend and shipmate, explained that fata morgana is an atmospherically triggered optical illusion that can make distant objects appear to hover. We checked the AIS, and our mirage was an actual ship plying actual brine.Given that we had hundreds of miles to go, there was time aplenty to ponderwhether AIS could also experience situational-awareness hiccups. The answer is yes, and the solution is already being developed. The VHF Data Exchange System (VDES), once operational, should make boating a better, safer and even more information-rich experience than it is today. To understand why, we need to start with AIS. On March 24,1989, the Exxon Valdez found the bricks in Alaska's Prince Williams Sound, triggering one of history's worst environmental disasters. A year later, as part of the Oil Pollution Act, lawmakers tasked the U.S Coast Guard with creating a vessel-tracking system (VTS) for tankers operating in the U.S Coast Guard Vessel Traffic Service in Alaska. The resulting system was based on VHF radio communications, as well as shore-based monitoring and polling systems. This system evolved into what became global AIS. By 2000, the International Maritime Organization began mandating that most sea-bound ships carry Class AAIS transmitters for collision-avoidance purposes and as a VTS tool. These transmitters broadcast information-including the vessel's name, position, course, speed, navigational status and unique MMSI number-on dedicated VHF channels 87B and 88B every two to 10 seconds, depending on vessel speed, while also listening for incoming AIS transmissions. In 2006, the AIS standards committee released specifications for a Class B-CS AIS system, which is a "polite" system that's interoperable with Class A AIS on a non-interference basis, for voluntary users. The Class B-CS employs the same two VHF channels, but it broadcasts every 30 seconds.In 2013, Class B-SO transmitters arrived. These operate on the same self-organizing bandwidth scheme as Class A systems; however, they transmit every five to 30 seconds. Overall, while there are many differences between Class A and Class B AIS transmitters, all AIS transmissions operate on just the two VHF channels: 87B and 88B. Given the amount of critical data that flows across these channels on crowded waters, bandwidth emerges as AIS' limiting factor.Enter VDES. The VHF Data Exchange System bundles existing technologies into one communications hub. VDES is composed of four key components: AIS, VDE Satellite, VDE Terrestrial and ASM channels. Much like modern smartphones that seamlessly tackle roaming and multiple frequencies, an onboard VDES box (once the system is operational, circa 2025 to 2035) should be able to listen to 12 different frequencies. These include two frequencies for satellite-based long-range AIS, two frequencies for sending and receiving AIS-based messages, six channels for receiving terrestrial or satellite-based data, and six channels for transmitting satellite data."The goal with VDES is to move non-ship-to-ship traffic off AIS so that AIS is primarily for collision avoidance, and for other marine-safety information to migrate to the other VDES channels," says Jorge Arroyo, a U.S Coast Guard program-and-management analyst. While all AIS devices will continue to work, unchanged, the overall system will be more efficient, robust and broader. "What I'm talking about today will hopefully be seamless in the future," he adds.While the ability to send updated navigational chart corrections or certain marine safety notifications via VDES offers a glimpse at the future, Arroyo envisions bigger dividends. "Real-time weather could be the killer app," h
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