NS100

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NS100

• Fundamentals of
• Naval Science

Gyro Compass
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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.
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(No Transcript)
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Gyro Compass Theory
Mechanics - A spinning wheel which is held
by two gimbals (Electronically
Stabilized) Physics - A gyro will always
point in one direction (Aligned to point
to True North) Precession - Apply a force to a
gyro and it will move, the earths
rotation causes a force that points a Gyro
toward True North .
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Gyro Applications

• Shipboard Use - There are usually two gyros
  which are 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.

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Gyro Applications(cont)

• Bridge - gyro repeaters are located on the
  bridge wings, navigation table, captains chair
  center line which is refereed to as centerline
  pelorus.
• CIC - repeaters located near the navigation
  table, TAOs chair, and DRT.
• Weapons - gyro inputs (i.e.. pitch/roll, heading
  yaw) are used by fire control computers

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First Gyro

• The first serially Gyro compass was installed
  aboard USS UTHAH on November 13, 1911

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True, Relative PGC Bearing

• True vs. Relative - Relative bearings cant be
  plotted on charts so they must be converted.
• Relative bearing Ships Head True Bearing
• True vs. PGC - Repeaters give a reading that does
  not account for Gyro Error
• Gyro Bearing Easterly Error True Bearing

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000 T
270 T
090 T
270 R
180 T
000 R
180 R
090 R
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True North
The target is due south of the ship (180T), but
is off the starboard beam, so the relative
bearing is 090 R.
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Ships head 090 T 000 R
True North
Ships head Relative Bearing True bearing 090
T 090 R 180 T
Relative Bearing 090 R
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True North
The target is still due south of the ship (180T),
but now it is off the port quarter, so the new
relative bearing is 225 R.
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True, Relative PGC BearingCont.

• Gyro Error - is the difference between the gyro
  reading and the true bearing.
• If Gyro is Least, Error is East
• If Gyro is Best, Error is West
• Example If Your are on a range bearing 089oT
  and the centerline pelorus reads 090o pgc, what
  is the gyro error?

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True, Relative PGC BearingCont.

• Gyro 090o and True 089o, Gyro Best F
  Error West
• 090o - 089o 1o
• Answer 1o Westerly Error

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Gyro Error in Navigation

• Causes of Error
• Friction
• Ships Motion
• Electronic Malfunctions
• Power Fluctuations
• Gyro Error - A gyro compass is a mechanical
  device with inherent error, the key is
  knowing the error and adjusting for it.

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Gyro Error in Navigation Cont.

• Determination of Error
• Visual Range.
• Adjusting Three LOPs (triangulation).
• Comparing a PGC bearing with a know true
  bearing.
• Celestial Azimuths and Amplitudes.
• Comparison with a Gyro of Known Error.

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Repeater Error

• GET Formula - The same type of correction
  applies as with Gyro Error.
• Repeater Error- The difference between a gyro
  repeater and the master gyro compass.
• Example The port bridge wing repeater reads
  187o and the master reads 190o with 2o
  East gyro error, what is the true bearing?

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Repeater Error Cont.

• Repeater 187o and Master 190o,
• Gyro Repeater Least FError East
• 190o - 187o 3o East
• True Gyro Error
• True 187o (3o E 2oE )
• True 187o 5o
• Answer 192o T

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Gyro Failure

• In the event gyro failure, the magnetic compass
  must be used. LOPs are taken in relative
  bearings. Then add the relative bearings to the
  magnetic heading to get a magnetic bearing.
• Rel. BearingMag. Ships HeadMag. Bearing
• Then the magnetic heading can be converted to
  true bearing by using CDMVT _at_ E formula.

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Review Questions
1. How does a gyro compass work ? 2. Convert
285o pgc to true bearing if gyro error is
5o E? 3. List three different methods of
determining Gyro Error? 4. Name three
users of gyro inputs?