Distrust AIS course and speed data, verify independently, and assess collisions using the full bridge picture. AIS dynamic information includes course over ground (COG) and speed over ground (SOG); COG is supplied when the connected position sensor calculates it, and SOG is supplied by the connected position sensor. COG or SOG may be unavailable, and poorly configured or calibrated position, speed or heading sensors can cause incorrect information to be transmitted.
MCA guidance distinguishes AIS target course and speed over ground from the course and speed through the water relevant to applying the COLREG, and says collision-avoidance decisions should be based primarily on systematic visual and/or radar observations. On a suitable display, received AIS motion data can support target tracking and calculations such as closest point of approach and time to closest point of approach, while remaining supplementary information.
