Navigation and Seamanship

1.1.3.2. Dead Reckoning (DR)

                        

              As man become bolder, he travelled beyond the range of visual reference to natural or manmade land marks. After proceeding to sea beyond visual range to land, the navigator can no longer use the piloting. He must then shift to alternative methods of determining position. He developed procedures to help him to estimate his position. The term is derived from “deduced reckoning” of sailing ships which is renamed as “dead reckoning”. Dead Reckoning (DR) is the fixing of a present position or anticipated (expected) future position, from a previous position using known directions and distances. In dead reckoning, projections are made from planned course and speeds without allowance for wind and current. Courses are determined by the compass, (magnetic or gyrocompass) and speed is taken from a log or count of engine revolutions. The plot of DR positions can be done either manually or by dead reckoning tracer which automatically analyses directions and distances and plot a continuous track. The DR position is only an approximation, because the wind, current, waves and steering errors are not taken to account. If there is no wind, current, waves and steering error then DR provides an accurate indication of position.