After a couple of hours of having disappeared from Marine Traffic whilst crossing the shipping lanes, my partner who was up in the early hours following my progress panicked and called Falmouth coastguard telling them she was concerned. They were very pleasant and reassuring and told her they could see me plodding along at 6 knots towards Falmouth so she shouldn't worry. They called me on VHF shortly after
Anyone following a boat via MarineTraffic or similar apps needs to be aware that it isn't 100% reliable. You can easily "vanish" from it because you simply aren't in range of any land base stations; I had a quick look at a few, and they seem to have rages of 10-20 nm mostly; you'd need a very high antenna to get much more than that. This will inevitably be true if you're doing an offshore passage, unless you pay for satellite data, which costs £46 a month, at least! I used it to follow a friend who is training as a ship's officer, and her ships always disappeared a few miles offshore, only to reappear a few days later near the destination.
Yes, but MarineTraffic also includes data from their phone app as pseudo AIS. I'm reasonably sure that it's someone using that. It never moves, so it's a matter of interest rather than a serious worry.
My boat was shown on Marine Traffic as being in Trinidad and Tobago for about 6 months. (It was actually in North Wales). Even now, although the location is corrected, it appears to be on an unending voyage back to Trinidad & Tobago! I gather that it’s possible to masquerade under any identity with the right equipment. Military craft on covert missions might want to appear as civilian traffic for example. But whether these misplaced AIS data are simple data corruption or something more nefarious, I’ve no idea. There doesn’t seem to be any way of correcting erroneous info in the system.
The problem is simply that MarineTraffic doesn't just include real AIS installations, but also includes "fake" ones that are generated by the phone app. Of course, they don't show up on a real AIS system, but they do show up in the app or on the website. In fact, I don't have an AIS transponder and was in fact using it in that mode - but I did enter the correct MMSI! As I'm installing a transponder later this year, I'll be interested to see what happens.