The document discusses gyrocompasses and magnetic compasses. It describes gyrocompass theory including how gyroscopes maintain orientation to true north. It also discusses gyro error determination and correction. Magnetic compass theory is explained including variation, deviation, and magnetic compass error. Methods to determine gyro error and apply corrections are provided along with examples of solving for true course from other compass readings.

1. NS100 Gyro and Magnetic Compass

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. 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. Gyro Compass Theory North-seeking gyroscope two gimbals Electronically Stabilized

5. Gyroscope

6. Gyro Compass Theory North-seeking Gyroscope Gyroscopic Inertia Gravity Precession

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.

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

12. Gyro repeater

13. Gyro Error in Navigation Causes of Error Friction Ship’s Motion Electronic Malfunctions Power Fluctuations. A gyro compass is an electronic/mechanical device with inherent error…. the key is knowing the error and adjusting for it

14. Gyro Error in Navigation Determination of Error Visual Range ( The most accurate ). Adjusting Three LOP’s (triangulation). Used before getting underway. Comparing a “PGC” bearing with a known true bearing. Celestial Azimuths and Amplitudes. Comparison with a Gyro of known error.

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

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

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

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? Gyro = 090 o and True = 089 o , Gyro = Best  Error = West 090 o - 089 o = 1 o Answer : 1 o Westerly Error

19. Summary pgc (per gyro compass) Gyro error  diff. True and Gyro norths

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.

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)

23. Summary pgc (per gyro compass) Gyro error  diff. True and Gyro norths M (magnetic) Variation  diff. True and Magnetic norths

24. Deviation Ship’s Magnetic Field

25. Deviation Degaussing

26. Compass Deviation table

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

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.

29. Applications of Compass Error Truly True Course Valiant Variation Marines Mag. Mer. Don’t Deviation Cry Compass @ Add Weddings West

30. Applications of Compass Error T = 125 o T V = 8 o West M = 125 + 8 = 133 D = 2.5 o East C = 133 + (- 2.5) Ans = 130.5 o pstgc

31. Summary pgc (per gyro compass) Gyro error  diff. True and Gyro norths M (magnetic) Variation  diff. True and Magnetic norths pstgc (per steering compass) Deviation  diff. Mag and steering compass norths