Course, Heading, and Bearing

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Course, Heading, and Bearing

“Course,” “heading,” and “bearing” describe related but non-interchangeable directions. Heading is the vessel’s orientation: it indicates where the bow is pointing. A course is the intended horizontal direction of travel, stated relative to a reference direction such as true north, magnetic north, compass north, or grid north. Course over ground (COG), by contrast, describes the vessel’s instantaneous direction of movement over the Earth’s surface. Wind and current can cause the vessel’s actual path to differ from the direction it is pointing.

An example with a cross-current

If the bow points east while a lateral current sets the vessel toward the south, the COG is south of the heading. There is no contradiction: heading describes orientation, while COG describes movement over the ground. The effect of the current depends on its strength and direction as well as the vessel’s speed through the water, so it cannot be expressed as a universally applicable fixed angle. Speed over ground and speed through the wateralso refer to different measurement references.

A planned course is a desired direction intended to achieve the required travel. In a cross-current, this desired direction may differ from the desired direction over ground. A route, on the other hand, is the intended path or a sequence of waypoints; it is not the same as a single course angle. In navigation, these terms are therefore clear only when it is specified whether they refer to a planned steering direction, the vessel’s orientation, or its actual movement.

Key terms at a glance

• Heading: The vessel’s orientation, or the direction in which the bow points; the reading may be referenced to true or magnetic north.
• Course: The intended horizontal direction of travel, measured from a clearly stated reference direction.
• Course over ground (COG): The instantaneous direction of movement over the Earth’s surface. A recorded track line, by contrast, connects successive positions to show the path traveled.
• Bearing: The angular direction of an observed object from a specified position, measured relative to a reference direction. A true bearing is referenced to true north; a relative bearing is measured clockwise from the bow to the object.

If a lighthouse lies northwest of the vessel, the bearing describes the direction from the observer’s position to the lighthouse. On its own, it says neither which way the bow is pointing nor the direction in which the vessel is moving over the ground. A relative bearing changes with the vessel’s orientation; the observer’s position and the time of observation also matter when determining the relationship to the object. The terms port, starboard, bow, and stern help describe a relative direction aboard a vessel.

To find a true bearing from heading and relative bearing, the angles can be added: true bearing = true heading + relative bearing, then normalized to the range from 0° to less than 360°. If the sum is exactly 360°, it is equivalent to 000°. This calculation applies only if the heading is referenced to true north; a magnetic or compass value would first need to be converted to the same reference. A bearing is therefore always understood together with its reference. Learn more about position relative to the wind in windward and leeward.