Heading versus COG

[Chuck - Raymarine - Moderator]

Heading versus COG

Heading describes the direction that a vessel is pointed at any time relative to the magnetic north pole or geographic north pole. As such, a stationary vessel (ex. a vessel which has been tied to a dock) will have a heading associated with the vessel's orientation. Sources of heading data include magnetic north seeking sensors (ex. an Evolution autopilot's EV-1 Sensor Core, an instrument compass, etc.), gyrocompasses, and GPS compasses (not to be confused with a common GPS sensor (ex. Raystar 130, Raystar 150, the internal GPS receiver of a MFD, etc.). Please click here to view a FAQ addressing features which require heading data. Should one desire to add a source of heading data to the system, then a stabilized heading source supporting 10Hz or greater heading updates is recommended (ex. Raymarine EV-1 CCU, Airmar H2183, KVH AutoComp 1000, etc.). Raymarine's EV-1 CCU has the advantage of being similarly priced to the other sensor alternatives and is a core component of an Evolution autopilot. As such, should the system ever be expanded to include an autopilot, then the EV-1 Sensor Core could be removed from the list of required autopilot components.

Course Over Ground (COG) describes the direction of motion with respect to the ground that a vessel has moved relative to the magnetic north pole or geographic north pole. Accordingly, should a vessel be stationary, it has no COG. Under conditions where a vessel is experiencing leeway (wind, current), a vessel's heading and COG may differ. This difference will typically be largest for vessels moving a slow speeds and in a direction which is not parallel to the direction of the leeway vector. The source of COG for most modern marine electronics sytems is a GPS sensor / receiver, which may internal or external to the vessel's chartplotting system.

While Raymarine product documentation is intended to provide information concerning the procedures for installation and use of its products, this documentation is not designed to teach navigation and seamanship. Information concerning these subjects may be found within publications addressing the subject of navigation (ex. The American Practical Navigator, Chapman Piloting & Seamanship, etc.) and training available from organizations (ex. United States Power Squadron, U.S. Coast Guard Auxiliary, etc.) and private enterprises dedicated to such training (ex. BoatWise, etc.). Many Raymarine dealers will additionally offer training on the use Raymarine products.


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