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Origins and Primary Areas of Navigation, Continued
Dead Reckoning
Dead reckoning (DR) can be defined as projecting an intended course
and speed from a known point. As our early navigators ventured further
from land, they needed a method to estimate position. With no visible
landmarks to use as a reference, early navigators estimated course and
speed on the chart. Dead reckoning does not consider the effects of
wind or current.
Figure 1-1 illustrates a sample DR plot. From the 0800 fix the ship’s
course and speed is plotted. A DR plot is maintained on board naval
vessels under way at all times.
It is the best estimate of where the ship
should be at any given time.
The DR plot also gives the navigator a
visual sign of whether the ship is steering towards danger or not. The
DR plot will be covered in greater detail in chapter 8.
Figure 1-1. Example of a DR track.
Celestial
Navigation
Celestial navigation may be defined as the practice of observing celestial
bodies (the Sun, Moon, stars, and planets) to determine the ship’s
position.
The early navigators recognized the need to overcome the shortcomings
of dead reckoning.
They soon developed techniques to observe the
heavenly bodies to determine their position. Although the instruments
used first were crude, they have steadily improved. An experienced QM
may now obtain a celestial fix within one-tenth of a mile of the ship’s
position.
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