1. COEFFICIENT D

2. Coefficient ‘D’
It is the mathematical representation of deviations on Intercardinal headings.
There are 2 causes:
Induction into Continuous F & A Horizontal Soft iron
&
Induction into Continuous Athwartships Horizontal Soft iron

3. Coefficient ‘D’ Quadrantal Named in the first quadrant (NE)
Only affected by the Hf component of the earths magnetic field
Only visible when the other coefficients have been removed

4. N NE
Coef ‘B’ E SE
Coef ‘C’ S SW W NW N

5. Induction into Continuous F & A Horizontal Soft iron
WESTERLY DEVIATION

6. Induction into Continuous Athwartships Horizontal Soft iron
EASTERLY DEVIATION

7. Nett effect F & A Horizontal Soft iron – WESTERLY Deviation
Thwartships Horizontal Soft iron – EASTERLY Deviation
DEV.
Small EASTERLY DEVIATION

8. ?
SE heading
What’s the deviation?

9. I nduced
C ontinuous
H orizontal
A thwartships
S oft iron

10. COEFFICIENT +D NE
EASTERLY DEVIATION

11. COEFFICIENT +D
WESTERLY DEVIATION SE

12. COEFFICIENT -D NE
WESTERLY DEVIATION

13. COEFFICIENT -D
EASTERLY DEVIATION SE

14. COEFFICIENT - D NE
WESTERLY DEVIATION

15. Correction Kelvin’s sheres Hollow soft iron
Provide discontinuous soft iron
Correct size of the spheres to match the +D of the ship
Sliding brackets – if there is a small residual +D slide the spheres closer
Spheres will work whatever the dip angle
No change with latitude as forces remain in proportion

16. Effect of Flinders Bar NE
WESTERLY DEVIATION

17. Coef A
Real A
Induction into Asymmetrical horizontal Soft Iron – i.e. binnacle is not on the centre line
Same size and sign on all headings
Apparent A
Azimuth ring/prism
Cockeye observations
Lubberline – i.e. not in the fore & aft line

18. Swing to find Coef’s A, B, C & D

19. Flinders bar in place
Set the spheres half way in
B & C correctors in place
Swing & take bearings on cardinal & inter-cardinal headings
Compile a table of deviations

20. A B C D N 053° NE 052° E 048 ° SE 050° S 058 ° SW 066° W 064 ° NW 057°
HDG
Comp. brg.
Mag. Brg
DEV.
E/W
+/- A B C D N
053° NE
052° E
048 ° SE
050° S
058 ° SW
066° W
064 ° NW
057°

21. Masters checks after a long lay-up
Compass is part of the Safety Certificates
Sight check – pos’n,size & nos of correctors
Semi permanent poles in the soft iron correctors
Anneal (600° straw colour, cool naturally)/ roll around the deck
Gimbal – is it seized up? Clean & vaseline
Deflect test – 90° each way / smooth motion / time it each way
Bubbles in the fluid
Check the binnacle position – on and in f & a line
At sea perform a swing and compile a deviation card

22. Location of swing area Traffic Water depth ( > twice draft)
Bridges, outfalls, underwater cables etc
Magnetic anomalies
Target
Distance from target (>16nm)
Target not on principle bearing
Day / night

23. Comm’s
VTS
Coast Guard
Owner
Charterer
Flags - OQ

24. Full Compensation New ship after trials At the end of 1st voyage
After structural alterations
After serious damage & repairs
After being struck by lightening
After a long lay up
After a serious fire & repairs

25. Tentative swing At least once a year
After routine dry docking or annual survey
After carriage of magnetic cargoes or use of magnetic equipment
Check ‘B’ when crossing the magnetic equator

26. Tentative Swing Direction of swing – turning circle
Start on any cardinal heading
Eg Head & take bearings on E, S & W
Calculate the Magnetic bearing
On WEST remove ALL of the deviation
Head NORTH, take a bearing and remove ALL of the deviation
Head EAST, take a bearing and remove HALF the deviation
Head SOUTH , take a bearing and remove HALF the deviation
Head onto any inter cardinal heading and take a bearing and remove HALF the deviation
Head on the opposite heading, take a bearing and remove HALF the deviation
Make a full swing taking bearing to obtain a Deviation Card

27. Deviation Card Vessels name Date of correction
Position – provides an idea of Hf & Zf
Number and position of correctors
Table with a curve of deviations
Signature of Adjuster