Week 4

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:

AND COMPASS CORRECTIONS COMPASSES AND COMPASS CORRECTIONS

Steering Compass

Handbearing Compass

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

VARIATION Magnetic North True North Easterly Variations Westerly South

MAGNETIC BEARINGS 8° 63° 71° BEARING Magnetic Bearing 071° True North BEARING Magnetic Bearing 071° Variation 8°W True Bearing 063° Magnetic North 8° 63° 71°

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

EFFECT OF COMPASS DEVIATION W E N S W E N S W E N S W E

DEVIATION CHECK Transit bears: True 305° Variation 8°W Magnetic 313° North Transit bears: True 305° Variation 8°W Magnetic 313° Compass 308° DEVIATION 5°E Magnetic North 8° N 305°(T) W E S

Deviation Card

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

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

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

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

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

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

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

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.

Wk 4 – Q 3 & 4 CTS