Knowra Dead reckoning Dead reckoning Dead reckoning estimates a vessel’s current position by advancing its last known position according to its course and speed over elapsed time. Its accuracy declines as measurement errors and unaccounted environmental forces accumulate.
Course over ground : The direction a vessel moves across Earth’s surface, measured relative to true or magnetic north. Dead reckoning needs the vessel’s actual direction of travel, not merely its heading.
Latitude : A geographic coordinate measuring angular distance north or south of the Equator. It is one coordinate used to record the starting and estimated positions.
Celestial navigation : A navigation method that determines position from observations of celestial bodies and time. Celestial observations can provide position fixes that correct dead-reckoning error.
Marine navigation : The planning and conduct of a vessel’s movement across waterways and oceans. Dead reckoning has long provided a way to maintain an estimated position between observations.
Speed over ground : A vessel’s speed relative to the ground beneath it, incorporating the effects of currents. Multiplying this speed by elapsed time gives distance traveled for a position estimate.
Longitude : A geographic coordinate measuring angular distance east or west of the Prime Meridian. Together with latitude, it specifies the location advanced by the estimate.
Satellite navigation : Navigation using signals from satellites to determine position, velocity, and time. Satellite-derived positions can replace or update an estimate based on prior motion.
Log (nautical) : An instrument or record used to measure a vessel’s speed or distance traveled. Log readings supply the speed or distance input for a dead-reckoning calculation.
Heading (navigation) : The direction a vessel’s bow points, measured relative to a reference such as true north. When course over ground is unavailable, heading can guide the estimate but may differ from the track.
Nautical mile : A unit of distance equal to 1,852 meters, corresponding approximately to one minute of latitude. Navigation commonly expresses the distance traveled during a dead-reckoning interval in nautical miles.
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