"The automatic identification system (AIS) is an automatic tracking system used on ships and by vessel traffic services (VTS). When satellites are used to detect AIS signatures, the term Satellite-AIS (S-AIS) is used. AIS information supplements marine radar, which continues to be the primary method of collision avoidance for water transport." — Automatic Identification System
rtl_ais, a simple AIS tuner and generic dual-frequency FM demodulator OS: Linux, Windows, OSX. Hardware: RTLSDR
Run:
$ sh /ais.sh
This script will download and install the rtl-ais, opencpn, and necessary libraries. (88 MB total downloads)
There are a range of AIS decoders to experiment with.