1. Masters Compass - Today’s Lesson
Basic Magnetism & the Earths field
Hf & Zf
Induction
Effect of the Earths’ field on new build vessels
Compass correcting – what are we correcting?
Card System
Coefficients
Coef. ‘B’ – Induced
Coef. ‘B’ – Permanent
Splitting ‘B’
Coef. ‘C’

2. Magnetism

3. LINES OF FORCE
EXIT RED POLE
ENTER BLUE POLE

4. FORCE FIELD RUNS FROM RED to BLUE
RED END ‘EMITS’
BLUE END ‘COLLECTS’

6. N (MAG)
S (MAG)

9. Opposite poles Attract
Like poles Repel
Opposite poles Attract

10. Hf & Zf
F’wood - 68

11. RATIO OF Hf & Zf
ASHORE Hf Hf Zf Zf
HIGH & LOW NORTH LAT.

12. Hf & Zf
@ Freetown Hf =
Zf =
@ NW Canada Hf =

13. Hf & Zf RATIO’s SHIP SHORE

14. Induction

15. WHERE FIELD ENTERS ‘BLUE’ POLE INDUCED
WHERE FIELD EXITS ‘RED’ POLE INDUCED

16. Hard & Soft Iron Ferro-magnetic materials - iron, steel, nickel
Non-magnetic - brass
Hard Iron retains magnetism becoming Permanent magnets
Soft Iron quickly loses it’s magnetism and is then re-induced by another field

17. FLINDERS BAR IS INDUCED SOFT IRON
HAS HORIZONTAL POLES & VERTICAL POLES

18. Effect of Earths field on a New build vessel

19. BUILT HEADING NORTH - NORTH LAT.

20. BUILT HEADING SOUTH - NORTH LAT.

22. Compass correction
What are we correcting?

23. ‘like cures like’
Forces acting on the compass position are practically equal in all directions of the ship’s head
Lost directive force on certain headings have been restored and sluggish action has been eliminated
Compass card has been steadied
Residual deviations are small and symmetrical

24. Card System Driving force? Where will it work best?
Magnet system – needle or ring
Magnet casing – brass
Float - High centre of gravity.
Jewel - sapphire
Pivot - iridium
Liquid - Bayol

25. Coefficients
A coefficient is a mathematical representation of deviations on two opposite headings.
Named by the deviation caused in the 1st sector. East is ‘+ve’. West is ‘-ve’.
Sectors : Semicircular or Quadrantal

26. Semicircular

27. Quadrantal

28. Coefficient ‘B’ BI – ‘B’ induced & BP – ‘B’ permanent
It is the mathematical representation of deviations on EAST & WEST headings.
There are 2 causes:
BI – ‘B’ induced
&
BP – ‘B’ permanent

29. Cause: induction of fore & aft, vertical soft iron near the binnacle
Coef. ‘B’ Induced
Cause: induction of fore & aft, vertical soft iron near the binnacle

30. Vertical iron induced
Northern hemisphere

31. Vertical iron induced
Southern hemisphere

32. ( NORTHERN HEMISPHERE )
INDUCED B
( NORTHERN HEMISPHERE )
What will be the deviation?

33. ( NORTHERN HEMISPHERE )
INDUCED B
( NORTHERN HEMISPHERE )
What will be the deviation?

34. ( NORTHERN HEMISPHERE ) What will be the deviation?
INDUCED B
( NORTHERN HEMISPHERE )
What will be the deviation?

35. ( NORTHERN HEMISPHERE ) COMPENSATION WITH FLINDERS BAR
INDUCED B
( NORTHERN HEMISPHERE )
COMPENSATION WITH FLINDERS BAR
( BLUE POLE )

36. ( SOUTHERN HEMISPHERE ) COMPENSATION WITH FLINDERS BAR
INDUCED B
( SOUTHERN HEMISPHERE )
COMPENSATION WITH FLINDERS BAR
( RED POLE )

37. What about at the Equator?

38. Cause: ships’ fore & aft magnetic field
Coef. ‘B’ Permanent
Cause: ships’ fore & aft magnetic field

45. COEFFICIENT +B E
EASTERLY DEVIATION
( BLUE BOW )

46. COEFFICIENT +B W
WESTERLY DEVIATION
( BLUE BOW )

47. Calculate the value of Coef ‘B’
When heading East the deviation was 10W
When heading West the deviation was 8E
E is +ve W is -ve
Change the sign on West, find the sum of the values and divide by 2

48. Calculate the value of Coef ‘B’
When heading East the deviation was 10W
When heading West the deviation was 8E
-10 -8
-18 divided by 2
= Coef. ‘B’ combined

49. Bp - Correction

50. Splitting ‘B’ Magnetic Equator method 2 different latitudes method
Adjusters method
Home coast method

51. Magnetic Equator method - example voyage
Compass corrected in Liverpool. Adjuster estimated the amount of Flinders Bar and corrected the remainder of Coef. B with permanent correctors
Ship sailed for Argentina
How is ‘B’ split?

52. Which ships don’t need a Flinders Bar?

53. Coefficient ‘C’
It is the mathematical representation of deviations on NORTH & SOUTH headings.
Cause: ships’ athwartship permanent magnetic field

54. COEFFICIENT +C N
EASTERLY DEVIATION
( BLUE STARB’D )

55. COEFFICIENT +C
WESTERLY DEVIATION
( BLUE STARB’D ) S

56. C - Correction

57. Obtaining a Magnetic bearing & calculating the value of Coef’s B & C

58. A B C D E N 052° NE 049 ° SE S 058 ° SW W 062 ° NW HDG Comp. brg.
Mag. Brg
DEV. A B C D E N
052° NE
049 ° SE S
058 ° SW W
062 ° NW

59. A B C D E N 051° 055° 4°E +4 NE 049 ° 6°E +6 SE S 058 ° 3°W -3 SW W
HDG
Comp. brg.
Mag. Brg
DEV. A B C D E N
051°
055°
4°E +4 NE
049 °
6°E +6 SE S
058 °
3°W -3 SW W
062 °
7°W -7 NW
13/2
=+6½
7/2
=+3½