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Lesson 10 Gyro And Magnetic Compass

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Lesson 10 Gyro And Magnetic Compass

  1. 1. NS100 Gyro and Magnetic Compass
  2. 2. 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.
  3. 3. 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.
  4. 4. Gyro Compass Theory <ul><li>North-seeking gyroscope </li></ul><ul><li>two gimbals Electronically Stabilized </li></ul>
  5. 5. Gyroscope
  6. 6. Gyro Compass Theory <ul><li>North-seeking Gyroscope </li></ul><ul><ul><li>Gyroscopic Inertia </li></ul></ul><ul><ul><li>Gravity </li></ul></ul><ul><ul><li>Precession </li></ul></ul>
  7. 10. 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.
  8. 11. Gyro Applications Bridge - 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
  9. 12. Gyro repeater
  10. 13. Gyro Error in Navigation <ul><li>Causes of Error </li></ul><ul><li>Friction </li></ul><ul><li>Ship’s Motion </li></ul><ul><li>Electronic Malfunctions </li></ul><ul><li>Power Fluctuations. </li></ul>A gyro compass is an electronic/mechanical device with inherent error…. the key is knowing the error and adjusting for it
  11. 14. Gyro Error in Navigation <ul><li>Determination of Error </li></ul><ul><li>Visual Range ( The most accurate ). </li></ul><ul><li>Adjusting Three LOP’s (triangulation). Used before getting underway. </li></ul><ul><li>Comparing a “PGC” bearing with a known true bearing. </li></ul><ul><li>Celestial Azimuths and Amplitudes. </li></ul><ul><li>Comparison with a Gyro of known error. </li></ul>
  12. 15. A 5 º westerly error VA bears 090 º T. With reference to the Gyro compass it would bear 90 º+5º= 95 º pgc VA
  13. 16. A 5 º Easterly error VA bears 090 º T. With reference to the Gyro compass it would bear 90 º-5º=85º pgc VA
  14. 17. 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 East If Gyro is Best , Error is West G yro bearing + E asterly Error = T rue bearing
  15. 18. Gyro error If you are on a range bearing 089 o T and the centerline pelorus reads 090 o pgc,what is the gyro error? <ul><li>Gyro = 090 o and True = 089 o , </li></ul><ul><li>Gyro = Best  Error = West </li></ul><ul><li>090 o - 089 o = 1 o </li></ul><ul><li>Answer : 1 o Westerly Error </li></ul>
  16. 19. Summary <ul><li>pgc (per gyro compass) </li></ul><ul><ul><li>Gyro error  diff. True and Gyro norths </li></ul></ul>
  17. 20. 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. Bearing Then the magnetic heading can be converted to true bearing.
  18. 22. 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)
  19. 23. Summary <ul><li>pgc (per gyro compass) </li></ul><ul><ul><li>Gyro error  diff. True and Gyro norths </li></ul></ul><ul><li>M (magnetic) </li></ul><ul><ul><li>Variation  diff. True and Magnetic norths </li></ul></ul>
  20. 24. Deviation Ship’s Magnetic Field
  21. 25. Deviation Degaussing
  22. 26. Compass Deviation table
  23. 27. Magnetic Compass Error Deviation + Variation = Compass Error If observed bearing is Least , Error is East . If observed bearing is Best , Error is West . Example: Deviation is 2 o West & Variation is 13 o East, what is compass error? Answer: 13 o - 2 o = 11 o East Error
  24. 28. Applications of Compass Error Scenario: The USS Boxer just lost it’s gyro compass while steering 125 o T . The conning officer needs to give a magnetic compass course. What course do you recommend? Given: Variation is 8 o West from the compass rose on the chart, annual increase was added to the variation. Deviation is 2.5 o East from the ship’s compass card for course 133 o M.
  25. 29. Applications of Compass Error <ul><ul><ul><ul><ul><li>Truly True Course </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Valiant Variation </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Marines Mag. Mer. </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Don’t Deviation </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Cry Compass </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>@ Add </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Weddings West </li></ul></ul></ul></ul></ul>
  26. 30. Applications of Compass Error <ul><ul><ul><ul><ul><li>T = 125 o T </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>V = 8 o West </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>M = 125 + 8 = 133 </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>D = 2.5 o East </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>C = 133 + (- 2.5) </li></ul></ul></ul></ul></ul>Ans = 130.5 o pstgc
  27. 31. Summary <ul><li>pgc (per gyro compass) </li></ul><ul><ul><li>Gyro error  diff. True and Gyro norths </li></ul></ul><ul><li>M (magnetic) </li></ul><ul><ul><li>Variation  diff. True and Magnetic norths </li></ul></ul><ul><li>pstgc (per steering compass) </li></ul><ul><ul><li>Deviation  diff. Mag and steering compass norths </li></ul></ul>

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