1. Week 4

2. Rules 1 to 10 – confirmation questions Wk 4 – Ex 1 1940 The Compass
Expected Learning Outcomes
At the end of the session, the students:
Will have confirmed their knowledge of IRPCS Rules 1- 10
Have learnt about Variation, Deviation and Compass Error
Time
Topic
Activity
Resources
1900
Introduction
Welcome
Tonight’s programme
Exercise 1 – progress
1910
ROR
Rules 1 to 10 – confirmation questions
Wk 4 – Ex 1
1940
The Compass
Types
Positioning
Variation
Deviation – including compass swing and adjustment
Compass Error
Presentation:
Compass
2030
Exercise
CTS and EP with deviation
Exercise sheet
Wk 4 – Ex 2
2055
Conclusion
Summarise today’s session
Work for next week:

3. AND COMPASS CORRECTIONS
COMPASSES
AND
COMPASS CORRECTIONS

4. Steering Compass

5. Handbearing Compass

6. Sources of Compass Error
Compass close to:
Magnets, iron or steel.
Current carrying wires.
Loudspeakers.
Mobile phones.

7. VARIATION Magnetic North True North Easterly Variations Westerly
South

8. MAGNETIC BEARINGS 8° 63° 71° BEARING Magnetic Bearing 071°
True
North
BEARING
Magnetic Bearing 071°
Variation °W
True Bearing °
Magnetic
North 8°
63°
71°

9. DEVIATION Similar in application to variation
Varies with boat's heading
Need a current Deviation Chart for each fixed
compass on board
Not used with handbearing compass
(but need to check for gross errors)
Need to swing compass annually and check
deviation occasionally

10. EFFECT OF COMPASS DEVIATIONW E N S W E N S W E N S W E

11. DEVIATION CHECK Transit bears: True 305° Variation 8°W Magnetic 313°
North
Transit bears:
True °
Variation °W
Magnetic °
Compass °
DEVIATION °E
Magnetic
North 8° N
305°(T) W E S

12. Deviation Card

13. Compass Corrections
Steering compass corrected for VARIATION and DEVIATION.
Handbearing compass corrected for VARIATION only.

14. COMPASS CORRECTIONS
Variation is the angle between TRUE NORTH and MAGNETIC NORTH
Deviation is the difference between the COMPASS BEARING and MAGNETIC BEARING
Conversions -
CADET
Compass  Add East  True
CADBURYS DAIRY MILK VERY TASTY
Compass +/- Deviation  Magnetic +/- Variation  True
Compass Error is the combined effect of Variation and Deviation

15. Using the Portland Plotter
Mark variation as an error of 7 °W
Handbearing Compass
Compass Brg = 154°M
Variation = 7°W
True Brg = ?

16. Using the Portland Plotter
Handbearing Compass
Compass Brg = 154°M
Variation = 7°W
True Brg = ?
Set 154M against the 7W error mark
Read True Brg at 0 error mark

17. Deviation and Variation
Compass Course = 215 C
Deviation for 215 (from curve) = 3E
Variation = 7W
Compass error = 4W

18. Solve with the Plotter
Course from Compass = 215 C
Deviation for 215 (from curve) = 3E
Variation = 7W
Compass error = 4W
Read the True course at the 0 error mark
Set the compass course against the 4W error mark

19. CTS – From Chart to Helm T True Course From Chart Apply variation
Magnetic Course
Apply deviation for the magnetic course
Compass course
Correct for expected leeway V
+ W
- E M D C

20. Dip Error
The lines of force of the Earth’s magnetic field are horizontal at the Equator.
As you move towards the magnetic poles the lines are angled (the Dip angle) towards the Earth.
This causes additional friction on the card pivot.
Presents a greater problem to aircraft than boats.

21. Wk 4 – Q 3 & 4
CTS