Lesson 10 Gyro And Magnetic Compass
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Transcript of Lesson 10 Gyro And Magnetic Compass
Objectives:1. Discuss gyrocompass theory and shipboard application.
2. Describe the differences and relationships of true bearings, relative bearings and “per gyro compass” (PGC) bearings.
3. Discuss and describe gyro error and the methods used to determine gyro error.
4. Demonstrate how to determine and correct for gyro error.
Objectives:
5. Describe the purpose and operation of the magnetic compass.
6. Discuss magnetic theory and application.
7. Define, identify, and solve for variation, deviation, compass error, magnetic bearings and true bearings.
Gyro Compass Theory
•North-seeking GyroscopeGyroscopic InertiaGravityPrecession
Gyro Applications Shipboard Use - two gyros placed deep in the ship on the centerline.Primary- (Master gyro) oriented to north/south, used for navigation &
shiphandling.
Auxiliary- (Back up gyro) oriented east/west, used for combat
systems.
Gyro ApplicationsBridge - gyro repeaters are located
on the bridge wings, navigation table, captain’s chair & center line which is referred to as “centerline
pelorus.”
CIC - Command and Control System.
Weapons - gyro inputs (i.e.. pitch/roll), are used by fire control
computers
Gyro Error in Navigation
Causes of Error• Friction
• Ship’s Motion• Electronic Malfunctions
• Power Fluctuations.
A gyro compass is an electronic/mechanical device with inherent error…. the key is knowing the error and adjusting for it
Gyro Error in Navigation Determination of Error
• Visual Range ( The most accurate).
• Adjusting Three LOP’s (triangulation).
Used before getting underway.
• Comparing a “PGC” 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 bear 90º-5º=85º pgc
VAVA
Gyro error
Gyro 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 EastIf Gyro is Best, Error is West
Gyro bearing +Easterly Error =True bearing
Gyro errorIf you are on a range bearing 089
oT and the
centerline pelorus reads 090
opgc,what is the gyro
error? Gyro = 090o and True = 089o,
Gyro = Best Error = West
090o - 089
o = 1
o
Answer: 1o Westerly Error
Gyro Failure
In the event of gyro failure LOP’s are taken in relative bearings.
The magnetic compass can be used to know your ship’s head.
Rel. Bearing+Mag. Ship’s Head=Mag. BearingThen the magnetic heading can be converted
to true bearing.
The variation information is contained in the compass rose closest to the ship’s DR position
True Bearing = Magnetic Bearing + Variation(add East Variation or subtract West Variation)
Summary
pgc (per gyro compass)Gyro error diff. True and Gyro norths
M (magnetic)Variation diff. True and Magnetic norths
Magnetic Compass Error
Deviation + Variation = Compass ErrorIf observed bearing is Least, Error is East.If observed bearing is Best, Error is West.
Example: Deviation is 2o West & Variation is 13o East, what is compass error?
Answer: 13o - 2o = 11o East Error
Applications of Compass Error
Scenario: The USS Boxer just lost it’s gyro compass while steering 125o T. The conning
officer needs to give a magnetic compass course. What course do you recommend?
Given: Variation is 8o West from the compass rose on the chart, annual increase was added to
the variation.Deviation is 2.5o East from the ship’s
compass card for course 133o M.
Applications of Compass Error Truly True Course Valiant Variation Marines Mag. Mer. Don’t Deviation Cry Compass @ AddWeddings West
Applications of Compass Error
T = 125o T V = 8o West M = 125 + 8 = 133 D = 2.5o East C = 133 + (- 2.5) Ans = 130.5o pstgc