AIS Class B coverage limits

I’m very interested in the use of AIS on yachts, and not just as an aid to navigation, but also as a way of tracking boats. There is now a proliferation of websites which “aggregate” AIS transmission from boats and plot their position on a map. Probably the most popular of these is, which I have written about earlier. At first glance, that would make a terrific way of tracking cruising yachts along our coast. But is it?

Last weekend’s Sydney to Gold Coast race provided an opportunity to see the difference between class A (commercial shipping) and class B (leisure vessels, work boats) versions of AIS as a couple of the boats in the race carried AIS transponders. Here is what I found….

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