Download - Gyro and Magnetic Compass 1029
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NS100
Gyro and Magnetic Compass
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Objectives:1. Discuss gyrocompass theory and
shipboard application.
2. Describe the differences and relationshipsof true bearings, relative bearings and ³per gyro compass´ (PGC) bearings.
3. Discuss and describe gyro error and themethods used to determine gyro error.
4. Demonstrate how to determine and correctfor gyro error.
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Objectives:
5. Describe the purpose and operation of the magnetic compass.
6. Discuss magnetic theory and application.
7. Define, identify, and solve forvariation, deviation, compass error,magnetic bearings and true bearings.
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Gyro Compass TheoryNorth-seeking gyroscopetwo gimbals Electronically
Stabilized
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Gyroscope
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Gyro Compass Theory
North-seeking Gyroscope
Gyroscopic Inertia
GravityPrecession
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Gyro ApplicationsShipboard Use - two gyros placeddeep in the ship on the centerline.
Primary- (Master gyro) orientedto north/south, used for
navigation & shiphandling.
Auxiliary- (Back up gyro) oriented
east/west, used for combatsystems.
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Gyro ApplicationsBridge - gyro repeaters are locatedon the bridge wings, navigation
table, captain¶s chair & center linewhich is referred to as ³centerline
pelorus.´
CIC - Command and ControlSystem.
Weapons - gyro inputs (i.e..pitch/roll), are used by fire control
com uters
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Gyro repeater
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Gyro Error in Navigation
Causes of Error
Friction
Ship¶s Motion
Electronic Malfunctions Power Fluctuations.
A gyro compass is an electronic/mechanicaldevice with inherent error«. the key is
knowing the error and ad justing for it
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Gyro Error in Navigation
Determination of Error Visual Range ( The most accurate).
Ad justing Three LOP¶s (triangulation).
Used before getting underway.
Comparing a ³PGC´ bearing with a known true
bearing.
Celestial Azimuths and Amplitudes.
Comparison with a Gyro of known error.
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A 5º westerly error
VA bears 090ºT.With reference to the Gyro compass it would bear
90º+5º=95º pgc
VAVA
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A 5º Easterly error
VA bears 090ºT.
With reference to the Gyro compass it would bear90º-5º=85º pgc
VAVA
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Gyro errorGyro Error - is the difference between the gyro
reading and the true bearing.
We can have a West or East Gyro error.If Gyro is Least, Error is East
If Gyro is Best, Error is West
Gyro bearing +Easterly Error =True bearing
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Gyro error If you are on a range
bearing 089oT and the
centerline pelorus reads
090opgc,what is the gyro
error? Gyro = 090o and True =
089o,
Gyro = Best Error = West 090
o- 089
o= 1
o
Answer : 1o
Westerly Error
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Summary
pgc (per gyro compass)
Gyro error diff. True and Gyro norths
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Gyro FailureIn the event of gyro failure LOP¶s are taken in
relative bearings.
The magnetic compass can be used to knowyour ship¶s head.
Rel. Bearing+Mag. Ship¶s Head=Mag. Bearing
Then the magnetic heading can be convertedto true bearing.
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The variation information is contained in the compassrose closest to the ship¶s DR position
True Bearing = Magnetic Bearing + Variation(add East Variation or subtract West Variation)
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Summary
pgc (per gyro compass)
Gyro error diff. True and Gyro northsM (magnetic)
Variationdiff. True and Magnetic norths
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DeviationShip¶s Magnetic Field
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DeviationDegaussing
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Compass
Deviation table
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Magnetic Compass ErrorDeviation + Variation = Compass Error
If observed bearing is Least, Error is East.
If observed bearing is Best, Error is West.
Example: Deviation is 2o West & Variation
is 13
o
East, what is compass error?Answer: 13o - 2o = 11o East Error
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Applications of Compass ErrorScenario: The USS Boxer just lost it¶s gyro
compass while steering 125o T. The conningofficer needs to give a magnetic compass
course. What course do you recommend?Given: Variation is 8o West from the compassrose on the chart, annual increase was added to
the variation.
Deviation is 2.5o
East from the ship¶scompass card for course 133o M.
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Applications of Compass Error
Truly True Course
Valiant Variation
Marines Mag. Mer.
on¶t Deviation
Cry Compass
@ A
ddWeddings West
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Applications of Compass Error
T = 125o T
V = 8
o
West M = 125 + 8 = 133
D = 2.5o East
C = 133 + (- 2.5)Ans = 130.5o pstgc
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Summary
pgc (per gyro compass)
Gyro error
diff. True and Gyro norths M (magnetic)
Variationdiff. True and Magnetic norths
pstgc (per steering compass)
Deviation diff. Mag and steering compass norths