Compass Examples

To convert from Compass to True : subtract differences to the West (variation or deviation)
To convert from True to Compass: add differences to the West

1. In 2004 the magnetic variation was 03 45' W (9'E) .When will the variation become 02 15'W ?

2. The magnetic variation is 4W and the compass heading is 188 (M). (Since the course has been given as (M) there is no deviation on this ship!) What is the true heading?

3.The magnetic variation is 6E . The compass heading is 067(M). What is the true heading?

4. The magnetic variation is 7W . From your chart you require a course 154 (T) What is the compass heading (M) ( no deviation on this ship)

5. The magnetic variation is 4W and the ship deviation table is shown below. The compass course is 135(C) what is the true course? (T)

6. From your chart you require a course 263(T). Magnetic variation is 7W and the ship deviation table is shown below. What is the compass course? (C)

Solutions

1. Difference in variation = final - initial value = 02 15' - 03 45' = - 01 30' = -90'
Annual change = 9'E = -9'
Time difference = total change/annual change = -90/-9 = 10 years
New value obtains 2004 + 10 = 2014

2    Heading = 188(M)
          - variation 4W
      Heading = 184(T)

3    Heading = 067(M)
         + variation 6E
      Heading = 073(T)

4.   Heading = 154(T)
         + variation 7W
      Heading = 161(M)

5.   Heading = 135(C)
         +deviation 6E
      Heading = 141(M)
          -variation 4W
      Heading = 137(T)

6.   Heading = 263(T)
          +variation 7W
       Heading = 270(M)
          +deviation 4W
       Heading = 274(C)

Leeway and Compass Course

1. The boat is running before a southerly breeze. To what extent is the course affected by leeway?

2. The wind is  NEbyE ; leeway is 5 degrees  boat heading is 000 (T). What is the true course?

3.The wind is from the North; leeway is 10 degrees and the boat heading is 090 (T). What is the true course?

4. Given the circumstances of question 3, what would be the course to steer in order to prevent the leeway from taking place?

5. Magnetic variation is 4 W. The wind is SW F4 and and the course is 280 (M). Given 6 degrees leeway what is the true course?

6. Magnetic variation is 4 W. The wind is W F5 and the course is 190 (M). Given 10 degrees  leeway what is the true course?

7. Magnetic variation is 6 E. The wind is E F6 and the course is 000 (C). Given 8 degrees leeway and the deviation table then what is the true course?

Solutions

1. Wind astern, no leeway.

2.  Heading 000(T)
     Wind to starboard, leeway is -5
     Heading is 000 - 005 = 355(T)

3. Heading 090(T)
    Wind to port, leeway is +10
    Heading is 090 + 010 = 100(T)

4. In order to prevent this leeway turn into the wind by an amount equal to the leeway angle.
    Heading is 090(T). Wind to port; turning into the wind by 010 gives a heading 090 - 010 = 080(T) in order to prevent the leeway.

5. Heading 280(M)
   -Variation 4W
    Heading 276(T)
    Wind to port, leeway is +6
    Heading 282(T)

6. Heading 190(M)
   -Variation 4W
    Heading 194(T)
   Wind to starboard, leeway is -10
   Heading 184(T)

7. Heading is 000(C)
   -Deviation 4W
  +Variation 6E
    Heading is 002(T)
    Wind to starboard, leeway is -8
    Heading is 002 - 008 = 354(T)

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