A DR plot is started from a previous established position. For our example, the last known electronic fix was at 04:00:00 UT, at location 38° 08.0' N, 053° 52.2' W. Ordered course and speed are 315°, 6 knots. Here, Chief Sheedy plots the last known electronic fix and the DR position up to 0800 UT.
A Navy navigator’s major concern is the accurate determination of the ship’s position. But it is not enough to know only the present position; equally important is calculating the ship’s position for a desired time in the future. For this, the navigator obtains the ship’s approximate present or future position by using a Dead Reckoning Plot.
In the U.S. Navy, a DR plot is always started from an established position; that is, an estimated position or a fix. In the U.S. Navy, only ordered courses and ordered speed are used to determine a DR plot. The effect of current is not considered in determining a DR position.
Although some of the details of dead reckoning are beyond the scope of this module, let’s look at our navigator making a DR plot.