Gyro and Magnetic Compass 1029

8/3/2019 Gyro and Magnetic Compass 1029

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NS100

Gyro and Magnetic Compass



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.



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.



Gyro Compass TheoryNorth-seeking gyroscopetwo gimbals Electronically

Stabilized



Gyroscope



Gyro Compass Theory

North-seeking Gyroscope

Gyroscopic Inertia

GravityPrecession



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.



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



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



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.



A 5º westerly error

VA bears 090ºT.With reference to the Gyro compass it would bear

90º+5º=95º pgc

VAVA



A 5º Easterly error

VA bears 090ºT.

With reference to the Gyro compass it would bear90º-5º=85º pgc

VAVA



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



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



Summary

pgc (per gyro compass)

Gyro error diff. True and Gyro norths



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.



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)



Summary


Gyro error diff. True and Gyro northsM (magnetic)

Variationdiff. True and Magnetic norths



DeviationShip¶s Magnetic Field



DeviationDegaussing



Compass

Deviation table



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



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.



Applications of Compass Error

Truly True Course

Valiant Variation

Marines Mag. Mer.

on¶t Deviation

Cry Compass

@ A

ddWeddings West



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



Summary


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

Gyro and Magnetic Compass 1029

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