Dead Reckoning

Dead Reckoning, basic method of navigation in which the position of a ship or aircraft is determined by calculation from a previous position of the craft, the direction of travel from the previous position, the speed of the craft, and the time travelled. It is difficult to plot the position of a vessel accurately solely by dead reckoning, because many unpredictable factors can affect the vessel's course, such as the effects of ocean currents and winds, the inaccuracy of the course steered, and the inaccuracy in the measurement of speed. Under the best conditions, a position determined by dead reckoning is subject to some error, and in storms or turbulent weather the error is greater. As a result, vessels navigating by dead reckoning must check their position periodically using celestial observation or electronic navigation systems to correct errors. Dead-reckoning positions can be calculated entirely by arithmetical methods, but they can also be determined by plotting the various distances involved on a chart and finding the position graphically by vector addition. These types of dead-reckoning calculation, however, are becoming obsolete with the advent of computers, and electronic and satellite navigation systems.