Navcom Passes

8/3/2019 Navcom Passes

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Navigation

Compasses

Navigation

Compasses



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



Gyr ocompass

Gyr oscope

3 axes

± Spin ± Torque

± Pr ecession

Gyr or epeater s

Spin axisSpin axis

Precession axisPrecession axis

Torque axisTorque axis



Compasses - A bbr eviations

Gyr ocompass PGC

Magnetic Compass

±Steer ing Compass PSTC

±Standar d Compass PSC



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.



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



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





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



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



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



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



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)







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



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



A pplying Var iation

Var iation is found by r efer encing the compass

r ose closest to the ship¶s position







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



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



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





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



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



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



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



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?



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.



Sample Pr oblem #2

C D M V T AE



Sample Pr oblem #2C D M V T AE

030




030 (-3)




030 (-3)

027




030 (-3)

027

Reinter polate - We assumed that the magnetic

head was 030, we now see it was 027



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



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)




030 (-3)

027

Reinter polate

027




030 (3)

027

Reinter polate

027

(11)




030 (3)

027

Reinter polate

027

(11)

016



Questions? Homewor k ± Read Chapter 8 pg. 129-147

1st Homewor k due Tuesday

2nd due Next Thur s

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