AIS Class B

A lower-power AIS transponder for vessels not required to carry Class A, typically fishing boats, workboats, and pleasure craft. Class B transmits at 2 W on a CSTDMA (or SOTDMA in B/SO units) access scheme and reports position less often than Class A, usually every 30 seconds underway. It carries MMSI, position, course, and speed but not rate of turn or full voyage data, and Class A units give Class B traffic lower display priority. It is not SOLAS-mandatory.