Clearing the AIS Log Jam
Once skeptics thought AIS wasn’t worth the bother. Now they worry the technology is working too well.
For about the same price as a pair of midrange binoculars, an Automatic Identification System (AIS) receiver can alert you to the presence of approaching vessels and tell you their names, courses, speeds, and closest points of approach (CPAs) while they are still beyond the horizon or a headland. Add in the cost of a decent radar reflector, and you could have an AIS B “transponder” that will give other ships’ watchkeepers nearly the same information about you as you are receiving from them. So what’s not to like?
For one thing, as AIS gains popularity and more and more AIS products appear at boat shows, in ship’s stores, and in catalogs, the technology is in danger of becoming a victim of its own success. The skeptics and cynics who once told us that AIS wouldn’t work are now telling us that it works too well, that navigation displays and radar screens are in danger of becoming so overloaded with AIS information that vital chart detail and radar contacts are being lost in the clutter. Whether the situation ever gets as bad as some people suggest is a matter of opinion. And if it does, it will certainly affect the small, overcrowded navigation displays used by recreational craft long before it poses a serious problem for the much bigger displays used on ships.
There are several possible solutions. One is to use a dedicated display to separate AIS data from the chartplotter or radar altogether. There are plenty of small chartplotters around that can handle AIS data. Why not use one as an AIS display, showing AIS information against a base map that displays coastlines and a maybe a few contours and place names?
Another solution is to filter what appears on the display. It sounds self-defeating: Why bother with AIS at all if you’re going to ignore it or at least parts of it? And the possibility that ships might filter out small craft from their bridge displays is one of the most powerful arguments in the cynics’ and skeptics’ armory.
But filtering is something we do instinctively, every time we go to sea. Navigating through a busy harbor, you may see hundreds of other boats but only take notice of the few that are of particular significance to you. You probably don’t pay much attention to vessels on moorings, for instance, until one of them lets go of its mooring ball and starts racing you to the fuel dock. And no matter how keen you are to avoid a close encounter with 50,000 tons of container ship, you’re unlikely to be panicking if you are looking at its stern rather than its bow.
Vesper Marine’s Watchmate AIS displays offer what are probably some of the best filtering options in the business, allowing you to pick one of four operating profiles: offshore, coastal, harbor, and anchored. Within each profile, you can customize the filters to suit your own preferences. In the system’s harbor mode, for instance, you might set the speed filter to 0.5 knots so that the display isn’t too cluttered with stationary vessels. Around the coast, on the other hand, you are probably just as interested in stationary vessels as moving ones (no one wants to hit a boat that has anchored up to go fishing), but you might set a CPA filter to a couple of miles to remove ships and boats that aren’t coming anywhere near you and set the TCPA (time to CPA) filter to half an hour to hide the ones that might come close at some stage but that you don’t need to worry about for the present moment.
These aren’t alarm settings. The Watchmate has those too, though they serve a completely different purpose, nor do they mean that you are ignoring vessels that have been filtered out. The system still electronically monitors every AIS message it receives and calculates the CPA and TCPA of every AIS target in range. If one of the filtered vessels does something that makes it interesting—like the moored boat letting go of its ball and starting to move—then it will reappear on the screen.
But filtering doesn’t mean forgetting, either. It simply means focusing on the things that matter most.
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This article originally appeared in the April 2011 issue of Power & Motoryacht magazine.