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Practical Application
Compass
Comparison
Whenever a ship is under way it is necessary to compare the ship’s
compasses to make sure that they are operating properly. This is
accomplished by using the compass calculations and checking the
compasses against the true course.
Example
The following table represents an excerpt from the Magnetic Compass
Record Book.
Date
Time
Latitude
Longitude
Gyro Compasses
True
Heading
---- Gyro
------Gyro
Gyro
Error
Gyro
Error
Reading
Reading
10Mar94
1000
36°24 W
74°12 W
120
1.0E
121
1012
36 04 W
074 14 W
270
1.0E
271
1025
36 05 W
074 18 W
297
1.0E
In this example the date, time, latitude, and longitude of the observation
are noted. The master gyro is reading 120; the error determined by the
morning azimuth is 1.0 E. Remember, if the compass is least the error
is east; you would add the error to obtain the true heading. Knowing
our true heading, we can now apply our variation and compare the
magnetic compasses.
Variation
Magnetic
MagneticCompasses
DG
Heading
ON/OFF
REMARKS
14 W
14 W
14.5W
135
285
Standard
Steering
Compass
Dev
Compass
Reading
Reading
Dev
136
1W
134
1E
OFF
289
4W
283
2E
OFF
Energized
degaussing at 1022
313
311
ON
As you can see, this is the practical application of your newly acquired
compass calculation skills. Practice by filling in the blanks for the 1025
entry. When under way, the compasses must be compared every
one-half hour and at each course change.
Note: There is an exception; if a ship is in a formation and changing
course frequently, or the ship is alongside another ship, each course
change does not need to be recorded. Use the following statement in the
Remarks column: "Steering various courses while alongside (in
formation)." A comparison must still be made every one-half hour!
2-18
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