AIS CPA and Limitations

AIS broadcasts a vessel's identity, position, course, speed, and other data. Plotters can calculate CPA and TCPA from AIS targets, making AIS extremely useful for identifying ships and planning early avoiding action.

AIS has limitations. Not all vessels carry it, not all units transmit accurate data, small craft may use lower-power Class B units, and data can be delayed or filtered. AIS is GPS-derived, so it shares GNSS vulnerabilities. It must complement lookout and radar, not replace them.