Magnetic compass: The coefficients are the mathematical ... - Rajnav

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29. 15 miles from a conspicuous object Free from traffic / focal point Away from metal structures, outfalls etc Deep water (UKC / Turning circle) No Magnetic anomalies 30. They are correcting for Coefficient E (Induce asymmetrical horizontal soft iron in F/Aft plane). Procedure for compass correction Tentative swing: Decide on the direction of swing Commence the swing (Tight turning circle) Obtain magnetic bearing of a distant object at all cardinals and get the average of this value which is the magnetic bearing. Head East take bearing and remove all deviation using F/A correctors (Bp) Head South take bearing and remove all deviation using Athwartship correctors (cp) Head West take bearing and remove Half of Deviation using F/A correctors Head North take bearing and remove Half of Deviation using athwartship correctors (cp) Head in NE (inter cardinal) heading take a bearing and remove half of the deviation using Spheres Head in SE take bearing and remove half of the deviation using F/A correctors (Bp) Make a full swing and get a deviation curve and see if the deviation observed is symmetrical and of low value. Analysis method: Analysis of the various deviations are carried out and correctors placed. A magnetic bearing is obtained and used as a reference to correct the deviation. If vessel’s position is exactly known the true bearing can be obtained and taken out from the variation gives the Magnetic bearing. A true bearing of the astronomical object should be continuously taken to ascertain the True bearing and subsequently the magnetic bearing can be obtained by taking off the variation. Co-efficient Bi – Flinder Bars Flinder bar is first placed to adjust the Bi. An approximated value is corrected for 3-4 degrees when the compass is heading east or west. On ships with +ve Bi (usually) the Flinder bar is placed Forward of the binnacle. In cases where there is –ve Bi (Funnel /Mast forward of the binnacle) the Flinder bar is placed aft of the Binnacle.
Coefficient D – Kelvin’s spheres Take a bearing on the cardinal heading (all four) and average out the magnetic bearing. Now obtain Bearing on Inter cardinal headings and average out the magnetic bearing. The difference in bearing is the deviation due to D. Correct it by adjusting the Spheres. Move the spheres closer till the deviation is removed. Heeling error correction: Co-efficient J Obtain the value of ships multiplier and adjust the shore to ship Hf ration using the VFI (Vertical force instrument). Use the VFI instrument and adjust the heeling error bucket position to cancel out the heeling error. The VFI is calibrated ashore. Vessel is steadied on the east west course and the bowl removed and replaced with the VFI in the same position as the compass needle would be. The Heeling error magnets are adjusted in number and position of buckets adjusted so as to make the VFI needle horizontal. Thus the heeling error is removed for that latitude. The Larger of the B or C should be corrected first. Permanent Bp – Head the vessel in East west direction obtain the Bearing and compare with the magnetic bearing obtain the deviation and using F/A magnets correct it. Permanent Cp - Head the vessel on North / South heading and obtain Bearing compare with magnetic bearing and obtain deviation. Using athwartship magnets correct it. Now corrections should be made for Ci and E and A if any. These are best left uncorrected and applied for. Carry out a complete swing and obtain deviation card. Confirm the low value of deviation and also the symmetry. Record all the position of the correctors. (Number and color) Position of carrying out the swing. Order of placing magnetic correctors: 1. Flinder bars: These should be placed first since they will correct Bi but create a D error which has to be corrected by the spheres. 2. The Kelvin’s spheres are to be used to correct D and they will also be correcting the 3 rd cause of Heeling Error (Athwartship horizontal). Their presence increase the directive force hence the bearings are better in quality and accuracy. 3. The heeling error corrector bucket for correcting (J) 4. Bp and Cp which ever of them is the largest.
Page 1 and 2: Magnetic compass: The coefficients
Page 3 and 4: Compass adjuster method: With his e
Page 5 and 6: 3. Magnetic bearing of an object is
Page 7: 22. The vessel should be in sea goi

Magnetic compass: The coefficients are the mathematical ... - Rajnav

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