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Ship's AIS


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AIS has been of great interest to all of us but I feel there is a bit of misunderstanding about it. This is my impression from an extended use. The underlines are for the TLDR crowd.


Origin -radar shows a ship where others are around them. AIS was nothing more than the idea of adding a little VHF radio that would tell the other guy what that blip on his radar screen is about. The starting point is your name so he can call you directly on his radio instead of saying "hey, ship on my left, which way do you want to turn?". Your direction, speed, size and ship type also help him understand what you are doing and the best way to fit that with what he wants to do. The VHF signal only reaches about 10-20 miles but that is enough for dealing with other ships in your path.


MarineTraffic.com -is the 2007 project of a shipping enthusiast originally in conjunction with a Greek maritime university. The founder realized that if onshore volunteers coupled VHF receivers with their home PC they could send their area's data over the internet to a central site and then it could be overlaid on a map made available on a web site. This has been a great resource and works well, its main limit however is that it only provides data when the ships are within range of a shore side volunteer.


Satellite era -MarineTraffic was a success with the industry as well as individuals, to the point where port authorities and others also put up receivers. Then the expanding satellite services on ships solved the problem of ships out of range. Once or twice a day they would send a satellite position message to a central service and MarineTraffic could subscribe to the data and distribute it.


The very important point here is that the last position shown by a shore radio receiver continues to be shown even when it is one hour to three days out of date because it's the best they've got. The satellite info can be newer than that but first it might only be hourly or once or twice a day and second it usually takes a paid subscription to see it. MarineTraffic does show these but they blank the ship details on their free service. If my cruise ship is the only one in the area going in my direction at my time then I can make a good guess but otherwise I'm out of luck.


Clones -there are a number of ship location websites. They may have some cosmetic differences and sometimes they are actually more friendly to cruise users. But their core data has likely come from a subscription to MarineTraffic's data. They may also be buying the satellite data. A key issue with some of them, especially the one from the travel agency in Germany, is that with his programming skill he has been able to take the schedules and place the ship's future travels on the maps. This is very nice for presenting a future cruise but when we are looking for right now it can fall down because if real data is not available he will default to the originally scheduled data. There is a box below the map that shows this.


Ship's data -the constantly changing speed, direction and position information is likely automatically put into the AIS information. The ship's name, type, origin, destination, ETA and other fixed data however is likely manually entered into the transmitter and thus depends on human upkeep. I have seen an "info for the day" chalkboard on several ship bridges and some have included that manual AIS info. That catch is that occasionally the destination seen was not up to date, unsurprisingly showing the ship you are passing today your correct destination for tomorrow is not very important. If you doubt that, we once had the Skybar clock out of whack for 3 days until a new CD boarded and asked us barflies what gives. It took her influence to get it reset. I have also seen cases where the AIS information was consciously incorrect. In one case the position data was offset by 4000 miles, the ship was actually in a pirate zone and didn't want to advertise. In another the ship type was changed to obscure it, perhaps because too many people onshore were likely tracking a seriously late arrival for turnaround that day and were liable to jump the gun about arriving at the terminal.


So do enjoy the AIS data but pay attention to the "received" time and don't be surprised if the destination data is wrong, especially during itinerary changes.



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