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Navigation
Compasses
Navigation
Compasses
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Gyr o Theory
A Gryr o compass is a Nor th Seeking
Gyr oscope
A spinning wheel held by two GIMBALS
Has 3 axies of angular f r eedom
± Spin Axis
± Hor izontal Axis
± Ver tical Axis
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Gyr ocompass
Gyr oscope
3 axes
± Spin ± Torque
± Pr ecession
Gyr or epeater s
Spin axisSpin axis
Precession axisPrecession axis
Torque axisTorque axis
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Compasses - A bbr eviations
Gyr ocompass PGC
Magnetic Compass
±Steer ing Compass PSTC
±Standar d Compass PSC
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Gyr o Theory
Physics ± A Gyr o Scope will always point in
one dir ection (in this case TRUE NORTH)
Pr ecision ± A pply for ce to the spin axis and the
gyr o scope will r otate, not in the dir ection in
which the for ce was applied but 90 degr ees
f r om that for ce vector.
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Gyr o Compasses
Ships nor mally have 2 gyr o compasses
± Main ± Or ientated N/S used for Navigation
± Auxiliary ± Or iented E/W for combat systems or as
a backup for Navigation.
Located deep within the ship
On the center line
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Gyr o Uses
Gyr o Repeater s
± Located on the br idge wings, Navigation Table,
Dead r eckoning plot
± Ar e used for Fir e Contr ol for gunnery systems ±
Pitch, yaw, and Roll
± Center line Pelor us ± Center of Br idge used as the
most accur ate r efer ence
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Gyr o Err or
Mechanical Device ± has some inher ent err or ±
THE KEY IS TO KNOW WHAT IT IS A ND
HOW TO CORRECT FOR IT
Sour ces of err or
± Mechanical Fr iction
± Ship¶s motion
± Electr onic malfunctions
± Power Fluctuations
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Deter mining Err or
Visual Range
Tr iangulation
± Adjusting thr ee or mor e lines of position to find
location and bear ing .
Compar e cour se with a known tr ue cour se
± Enter ing and exiting por t or in a channel
Celestial Azmiuths and Amplitudes
Compar ison with a gyr o of known err or
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Gyr o Err or
Err or ± the differ ence between the tr ue bear ing and the
Gyr o r eading
Expr essed in degr ees East or degr ees West
Gyr o Least, err or East
Gyr o Best, err or West
Gyr o Bear ing + East Err or = Tr ue Bear ing
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Err or Example
You ar e dead center on a Range Bear ing 173
Degr ees Tr ue and your Gyr o r eads 175
Degr ees PGC what is your Err or?
GYRO = 175 Tr ue = 173
GYRO is BEST ERROR is WEST175 ± 173 = 2 degr ees West
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Shipboar d Compasses
Thr ee pr inciple r efer ences of dir ection
± Ships longitudinal axis RELATIVE BEAR I NG (R )
± Local magnetic mer idian MAG NETIC BEAR I NG (M) ± Tr ue mer idian TRUE BEAR I NG (T)
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Relative Vs. Tr ue
Relative bear ings Can NOT be plotted so
must conver ted
Relative Bear ing + Ship¶s Head =Tr ue Bear ing
090 + 090 = 180
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Magnetic
The Ear th is a cor e of Ir on which acts as a lar ge
magnet with its poles aligned with the ear th¶s axis
NOT located at 090 Nor th Latitude
± Differ ence is VAR IATION
Magnetic Mer idians - Skewed due to
irr egular ities in the Ear th¶s
cor e
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A pplying Var iation
Var iation is found by r efer encing the compass
r ose closest to the ship¶s position
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Deviation
Each ship is made of Steel and Ir on
It has its own magnetic field that can effect changes in
the ship¶s magnetic compass
Deter mined by angle in which the Keel is laid dur inginitial constr uction
Equipment ± electr onics can also cause deviation
Expr essed in Degr ees Eastand West (r ounded to near est
.5 Degr ee)
Changes with the ship¶s heading
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Degaussing
Degaussing system - electr ical installation designed to pr otect ships against magnetic mines and tor pedoes
Pur pose ± counter act the ship¶s magnetic field andestablish a condition such that the magnetic field near theship is, as near ly as possible, just the same as if the ship
wer e not ther e
Degaussing installation consists of per manently installeddegaussing coils wr apped ar ound ship on under side of hull, contr ol unit to contr ol the coil curr ent, and compass
compensating equipment to pr event distur bances to magcompasses ± Coil is a lar ge diameter electr ical wir e
± A, F, L, M, Q Coils
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Compass Err or
Deviation + Var iation =
Compass Err or
Obser ved Bear ing Least =
Err or East
Obser ved Bear ing Best =
Err or West
Ex. Deviation = 3 West
Var iation = 13 West
3 + 13 = 16 West
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Example
USS Pr inceton is on cour se 125 degr ees tr ue
when you lose your gyr o scope. The
Navigation gives you the following:
Var iation = 8 degr ees West
Deviation = 2.5 degr ees East
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Example
Tr uly ± Tr ue Cour se = 125
Valiant ± Var iation = 8 W
Mar ines - Magnetic Cour se = 133 Don¶t - Deviation = 2.5 E
Cry ± Compass ± 133 ±2.5 = 130.5
Because of ADD WEST
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Compass Head What the mag compass r eads
Deviation
Magnetic Head What the magnetic heading is
Var iation
Tr ue Head What the tr ue heading is
AddEast
CanCan
DeadDead
MenMenVoteVote
TwiceTwice
AtAtElectionsElections
A pplication of Compass Err or
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Sample Pr oblem #1
Degaussing is ON
Ship¶s Magnetic Compass r eads 030° PSTC
Var is 11° W Find ship¶s tr ue head
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Inter polation
Bill and Jor ge decide to split a pizza.
The pizza costs $9.00 and has 6 slices.
Bill eats 5 slices Jor ge eats 1 slice
How much should Bill pay?
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Inter polation Eating all the pizza slices costs $9.00
Eating none of the pizza costs $0.00
So Bill has eaten 5/6 of $9.00
5/6 times $9.00 = $7.50
This is inter polation - calculation of an
inter nal value by assuming a linear
r elationship with surr ounding data.
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Sample Pr oblem #2
C D M V T AE
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Sample Pr oblem #2C D M V T AE
030
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Sample Pr oblem #2C D M V T AE
030 (-3)
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Sample Pr oblem #2C D M V T AE
030 (-3)
027
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Sample Pr oblem #2C D M V T AE
030 (-3)
027
Reinter polate - We assumed that the magnetic
head was 030, we now see it was 027
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Sample Pr oblem #2Reinter polate - We assumed that the magnetic
head was 030, we now see it was 027.
Value for 030 = 3.0W
Value for 015 = 3.5W
3.0W-3.5W = -0.5W
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Sample Pr oblem #2030 - 015 = 15 degr ees
027 - 015 = 12 degr ees
So we ar e 12/15 of the way f r om 015-030
12/15 times -0.5 = -0.4
BUT we r ound to the near est .5 so it is -0.53.5W - 0.5W = 3.0W
Or no change (in this case)
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Sample Pr oblem #2C D M V T AE
030 (-3)
027
Reinter polate
027
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Sample Pr oblem #2C D M V T AE
030 (3)
027
Reinter polate
027
(11)
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Sample Pr oblem #2C D M V T AE
030 (3)
027
Reinter polate
027
(11)
016
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Questions? Homewor k ± Read Chapter 8 pg. 129-147
1st Homewor k due Tuesday
2nd due Next Thur s