Risk of Collision

A situation in which the available information indicates that two vessels may collide unless appropriate action is taken.

A steady or nearly steady compass bearing with decreasing range is a strong warning, but appreciable bearing change does not always remove risk when approaching a very large vessel, a tow or at close range. All available means appropriate to the circumstances, including systematic radar observation where fitted, must be used.

If there is doubt, risk is treated as existing. Assessment requires adequate time, repeated observations and allowance for measurement and manoeuvre uncertainty; AIS closest-point predictions can assist but depend on transmitted and sensor data and do not replace visual and radar appraisal.