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AIS VHF vs AIS Satellite

Ok, what’s the difference and what you should know.

Firstly AIS, Automatic Identification system, that allows other boats to track your position is based on the transmission of a data packets from. your boat via VHF channels 87B (161.975 MHz) and 88B (162.025 MHz).

This means that your AIS location is available to other receivers within the transmission range of your VHF radio, or circa 20Nm tops. NOTE: you can get much better and much worse but this is a good general maximum working distance.

But how do you show up on trackers like MarineTraffic etc? Well the answer is that a shore station (or a satellite connected vessel) picks up your AIS VHF Signal and relays it onto the internet.

But there is a deferent version of AIS called AIS Satellite (S-AIS) which send AIS Data via satellite. I’m pretty sure you’d know if you have this :-).

So AIS is just line of sight VHF and you show up on the internet because of ground based AIS stations relaying your data. So, if you get out far from shore you’ll only show up if the QE2 relays your data… which happened to us just recently.

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  1. There are satellites with VHF AIS receivers. This is what S-AIS is all about. There is no different hardware on ships or boats for S-AIS. See . See also . Line of sight (LoS) is great, buy physics due to r-squared attenuation is not on our side, so you can expect a handful of Class A (commercial) position reports from a commercial vessel and one or two from a Class B (recreational) vessel.

    Generally you have to be extra to a provider (like MarineTraffic) for the satellite data feed. That’s for access to the data. There is no different equipment on the vessel.

    There are certainly satellite trackers (e.g. Garmin inReach) but they have nothing to do with AIS.

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