Determining the Ships Position Using Sextant Angles
Horizontal sextant angles give fixes of great accuracy that are not
affected by any error of the compass. A fix by horizontal sextant angles
is labeled the same as a visual fix with a small circle around the position
and the time of the fix close to the fix symbol.
Horizontal sextant angles used in conjunction with a computer-assisted
positioning program are the most common method used by the Coast
Guard to position aids to navigation.
Horizontal sextant angles should be taken as nearly simultaneously as
possible, preferably by two people on a predetermined signal. However,
one person can obtain both angles if the ship is not moving quickly.
Rule: To obtain a fix using sextant angles, you must have three fixed
visual objects, and those objects must be identifiable on the chart.
Follow these steps to obtain horizontal sextant angles:
Hold the sextant horizontally with your right hand.
View the left object directly through the telescope.
Release the index arm with your left hand on the release
levers and swing the arm so that the index mirror reflects the
center object in the horizon glass below the left object.
Rotate the micrometer drum to fine adjust the reflected
object in line with the object viewed directly.
Take a reading of the angle.
Do you have two people taking angles?
If yes, both angles are ready to be plotted.
If no, repeat steps 1 through 5 using the center object viewed
directly and the right object viewed reflected.