COEFFICIENT D

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

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

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

Induction into Continuous F & A Horizontal Soft iron WESTERLY DEVIATION

Induction into Continuous Athwartships Horizontal Soft iron EASTERLY DEVIATION

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

? SE heading What’s the deviation?

I nduced C ontinuous H orizontal A thwartships S oft iron

COEFFICIENT +D NE EASTERLY DEVIATION

COEFFICIENT +D WESTERLY DEVIATION SE

COEFFICIENT -D NE WESTERLY DEVIATION

COEFFICIENT -D EASTERLY DEVIATION SE

COEFFICIENT - D NE WESTERLY DEVIATION

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

Effect of Flinders Bar NE WESTERLY DEVIATION

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

Swing to find Coef’s A, B, C & D

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

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°

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

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

Comm’s VTS Coast Guard Owner Charterer Flags - OQ

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

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

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

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