Course Over Ground (COG)

The actual path a vessel follows over the surface of the Earth, as opposed to its heading or intended course.

Course Over Ground (COG) is a critical concept in navigation, representing the true direction in which a vessel is moving relative to the Earth’s surface. It is often measured in degrees from true north, and it accounts for the combined effects of various external forces, such as wind, current, and tide, which can push a vessel off its intended heading. While a vessel’s heading is the direction in which the bow is pointing, the COG reflects the actual trajectory the vessel is following. For example, if a boat is pointed due north (heading 0°) but a strong current is pushing it towards the east, the COG might show a course of 030° or more, depending on the strength of the current.

COG is typically determined using GPS systems, which track the vessel’s movement over time and calculate the resultant direction. It is an essential parameter for mariners to monitor, especially when navigating in challenging conditions, as it helps ensure that the vessel is on the correct path to its destination. By comparing the COG with the intended course (Course Made Good or CMG), mariners can make necessary adjustments to their heading to compensate for any drift or external forces affecting their journey. Understanding and monitoring COG is crucial for safe and efficient navigation, particularly in coastal or congested waters where precision is key.