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Navigation

Compasses

Navigation

Compasses

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Gyro Theory

AGryro compass is a North Seeking

Gyroscope

A spinning wheel held by two GIMBALS

Has 3 axies of angularfreedom

Spin Axis

Horizontal Axis

Vertical Axis

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Gyrocompass

Gyroscope

3 axes

Spin Torque

Precession

Gyrorepeaters

Spin axisSpin axis

Precession axisPrecession axis

Torque axisTorque axis

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Compasses - Abbreviations

Gyrocompass PGC

Magnetic Compass

Steering Compass PSTC

Standard Compass PSC

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Gyro Theory

Physics AGyro Scope will always point in

one direction (in this case TRUE NORTH)

Precision Apply force to the spin axis and the

gyro scope will rotate, not in the direction in

which the force was applied but 90 degrees

from that force vector.

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Gyro Compasses

Ships normally have 2 gyro compasses

Main Orientated N/S used forNavigation

Auxiliary Oriented E/W forcombat systems oras

a backup forNavigation.

Located deep within the ship

On the centerline

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Gyro Uses

Gyro Repeaters

Located on the bridge wings, Navigation Table,

Dead reckoning plot

Are used forFire Control forgunnery systems

Pitch, yaw, and Roll

Centerline Pelorus CenterofBridge used as the

most accurate reference

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Gyro Error

Mechanical Device has some inherent error

THE KEY IS TO KNOW WHAT IT IS AND

HOW TO CORRECT FORIT

Sources of error

Mechanical Friction

Ships motion

Electronic malfunctions

PowerFluctuations

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Determining Error

Visual Range

Triangulation

Adjusting three ormore lines of position to find

location and bearing .

Compare course with a known true course

Entering and exiting port orin a channel

Celestial Azmiuths and Amplitudes

Comparison with a gyro of known error

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Gyro Error

Error the difference between the true bearing and the

Gyro reading

Expressed in degrees East ordegrees West

Gyro Least, errorEast

Gyro Best, errorWest

Gyro Bearing + East Error= True Bearing

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ErrorExample

You are dead centeron a Range Bearing 173

Degrees True and yourGyro reads 175

Degrees PGC what is yourError?

GYRO = 175 True = 173

GYRO is BEST ERROR is WEST175 173 = 2 degrees West

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Shipboard Compasses

Three principle references of direction

Ships longitudinal axis RE LATIVE BEARING (R)

Local magnetic meridian MAGNETIC BEARING (M) True meridian TRUE BEARING (T)

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Relative Vs. True

Relative bearings Can NOT be plotted so

must converted

Relative Bearing + Ships Head =True Bearing

090 + 090 = 180

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Magnetic

The Earth is a core ofIron which acts as a large

magnet with its poles aligned with the earths axis

NOT located at 090 North Latitude

Difference is VARIATION

Magnetic Meridians - Skewed due to

irregularities in the Earths

core

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Applying Variation

Variation is found byreferencing the compass

rose closest to the ships position

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Deviation

Each ship is made of Steel and Iron

It has its own magnetic field that can effect changes in

the ships magnetic compass

Determined by angle in which the Keel is laid duringinitial construction

Equipment electronics can also cause deviation

Expressed in Degrees Eastand West (rounded to nearest

.5 Degree)

Changes with the ships heading

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Degaussing

Degaussing system - electrical installation designed toprotect ships against magnetic mines and torpedoes

Purpose counteract the ships magnetic field andestablish a condition such that the magnetic field neartheship is, as nearly as possible, just the same as if the ship

were not there

Degaussing installation consists of permanently installeddegaussing coils wrapped around ship on underside ofhull, control unit to control the coil current, and compass

compensating equipment to prevent disturbances to magcompasses

Coil is a large diameterelectrical wire

A, F, L, M, Q Coils

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Compass Error

Deviation + Variation =

Compass Error

Observed Bearing Least =

ErrorEast

Observed Bearing Best =

ErrorWest

Ex. Deviation = 3 West

Variation = 13 West

3 + 13 = 16 West

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Example

USS Princeton is on course 125 degrees true

when you lose yourgyro scope. The

Navigation gives you the following:

Variation = 8 degrees West

Deviation = 2.5 degrees East

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Example

Truly True Course = 125

Valiant Variation = 8 W

Marines - Magnetic Course = 133 Dont - Deviation = 2.5 E

Cry Compass 133 2.5 = 130.5

Because ofADD WEST

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Compass Head What the mag compass reads

Deviation

Magnetic Head What the magnetic heading isVariation

True Head What the true heading is

AddEast

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Application of Compass Error