All international voyage ships over 300 tonnes and all passenger ships are required by law to have an AIS (Automatic Identification System) transceiver fitted. This transceiver transmits on the VHF band with information such as position, heading and speed. All you need to listen in on these messages is a VHF antenna to pick up the signals and an AIS receiver to decode the messages. The dAISy AIS receiver made by Wegmatt LLC works with Windows, Mac, Linux and Android devices. You’ll also need a clear view of the sea, as most AIS transmissions from ships only be detected between 10-20 nautical miles away.
Screenshot of MarineTraffic website
Due to the fact that you can only pick up the signal from ships in a 10-20 nautical mile range, there are services out there that aggregate the data from receivers from all over the world and plot them on a map. MarineTraffic is one such example. You can view ships all over the world that are in range of an AIS receiver connected to the network which is very cool. It’s fun to check out nearby ships, they send out status’ like “engaged in fishing” or whatever it is they happen to be doing.
The dAISy receiver works by using the Si4362-C chip which is a low current receiver IC made by Silicon Labs and an MSP430 microcontroller. The design is open source, you can view the source code and PCB design files over on GitHub
