The DR Plot
The importance of maintaining an accurate dead reckoning plot cannot
be overemphasized. Since other means of fixing your ships position
may not always be available, a navigator must rely on a DR plot.
If a ship made good the exact course and speed ordered, and there was
no wind or current, dead reckoning would, at all times, provide an
accurate indication of the ships position. A navigator must know the
position, or approximate position, to determine when to make changes in
course and/or speed, to predict the time of sighting lights or other aids to
navigation, and to identify landmarks.
When maintaining a DR plot, there are six rules that govern what
actions the QM should take. These rules are not subject to
interpretation, they are hard and fast. Often, when the ship is changing
course it becomes tedious to maintain the DR plot. This is a given and
known fact; however, the importance of keeping the plot up to date cant
be stressed enough.
These rules specify when a DR position shall be plotted:
A DR position shall be plotted each hour on the hour.
A DR position shall be plotted at the time of every course
A DR position shall be plotted at the time of every speed
A DR position shall be plotted at the time of a fix or running fix.
A DR position shall be plotted at the time of obtaining a single
A new course line shall be plotted from each new fix or running