CHAPTER 6 MAGNETIC COMPASS ADJUSTMENT GENERAL PROCEDURES FOR MAGNETIC COMPASS ADJUSTMENT 600. Introduction f. Alignment of magnets in binnacle. g. Alignment of heeling magnet tube under pivot This chapter presents information and procedures point of compass. for magnetic compass adjustment. Sections 601 and 613 h. See that corrector magnets are available. cover procedures designed to eliminate compass errors satisfactorily. Refer to Figure 607 for condensed infor- 2. Physical checks of gyro, azimuth circle, and peloruses. mation regarding the various compass errors and their a. Alignment of peloruses with fore-and-aft line of correction. ship (section 610). The term compass adjustment refers to any change of b. Synchronize gyro repeaters with master gyro. permanent magnet or soft iron correctors to reduce normal c. Ensure azimuth circles and peloruses are in good compass errors. The term compass compensation refers to condition. any change in the current slupplied to the compass compen- sating coils to reduce degaussing errors. 3. Necessary data. a. Past history or log data which might establish 601. Adjustment Check-Off List length of Flinders bar (sections 610 and 623). b. Azimuths for date and observer’s position (section If the magnetic adjustment necessitates (a) movement 633 and Chapter 17). of degaussing compensating coils, or (b) a change of c. Ranges or distant objects in vicinity if needed (lo- Flinders bar length, check also the coil compensation per cal charts). section 646. d. Correct variation (local charts). Expeditious compass adjustment depends on the appli- e. Degaussing coil current settings for swing for resid- cation of the various correctors in an optimum sequence ual deviations after adjustment and compensation designed to minimize the number of correction steps. Cer- (ship’s Degaussing Folder). tain adjustments may be made conveniently at dockside, simplifying the at sea adjustment procedures. 4. Precautions. Moving the wrong corrector wastes time and upsets all a. Determine transient deviations of compass from previous adjustments, so be careful to make the correct ad- gyro repeaters, doors, guns, etc. (sections 636 and justments. Throughout an adjustment, special care should 639). be taken to pair off spare magnets so that the resultant field b. Secure all effective magnetic gear in normal seagoing about them will be negligible. To make doubly sure that the position before beginning adjustments. compass is not affected by a spare magnet’s stray field, c. Make sure degaussing coils are secured before be- keep them at an appropriate distance until they are actually ginning adjustments. Use reversal sequence, if inserted into the binnacle. necessary. d. Whenever possible, correctors should be placed A. Dockside tests and adjustments. symmetrically with respect to the compass. 1. Physical checks on the compass and binnacle. 5. Adjustments. a. Remove any bubbles in compass bowl (section a. Place Flinders bar according to best available infor- 610). mation (sections 610, 622 through 625). b. Test for moment and sensibility of compass nee- b. Set spheres at mid-position, or as indicated by last dles (section 610). deviation table. c. Remove any slack in gimbal arrangement. c. Adjust heeling magnet, using balanced dip needle d. Magnetization check of spheres and Flinders bar if available (section 637). (section 610). e. Alignment of compass with fore-and-aft line of B. Adjustments at sea. Make these adjustments with the ship ship (section 610). on an even keel and steady on each heading. When using 81 82 MAGNETIC COMPASS ADJUSTMENT the gyro, swing slowly from heading to heading and check Fore-and-aft and athwartship magnets Quadrantial spheres Flinders bar Deviation Easterly on east Westerly on east Deviation E. on NE, W. on NE, Deviation change E. on E. and W. on W W. on E. and E. on W and westerly on and easterly on E. on SE, E. on SE, with latitude when sailing toward when sailing toward west. west. W. on SW, W. on SW, change equator from north equator from north and andE. on NW. latitude or away from Spheres latitude or away from Magnets (+B error) (-B error) W. on NW. (-D error) equator to south Bar equator to south latitude. (+D error) latitude. No fore and aft Place magnets red Place magnets red No spheres on Place spheres Place spheres fore Place required of bar Place required amount magnets in forward. aft. binnacle. athwartship. and aft. No bar in holder. forward. of bar aft. binnacle. Fore and aft Raise magnets. Lower magnets. Spheres at Move spheres toward Move spheres Increase amount of bar Deacrease amount magnets red athwartship compass or use outwards or remove. Bar forward of binnacle. forward. of bar forward. forward. position. larger spheres. Fore and aft Lower magnets. Raise magnets. Spheres at fore and Move spheres Move spheres toward Decrease amount of Increase amount of magnets red aft. aft position. outward or remove. compass or use Bar aft of binnacle. bar aft. bar aft. larger spheres. Deviation Easterly on north Westerly on north Deviation E. on N, W. on N, W. on E. and E. on W. E. on E. and W. on W. and westerly on and easterly on W. on E, E. on E, when sailing toward when sailing toward south. south. E. on S, W. on S, Bar equator from south equator from south Magnets Spheres and and latitude or away from latitude or away from (-C error) W. on W. E. on W. Deviation change equator to north equator to south latitude (+C error) (+E error) (-E error) with latitude latitude. change No athwartship Place athwartship Place athwartship No spheres on Place spheres at port Place spheres at Heeling magnet magnets in magnets red magnets red port. binnacle. forward and starboard starboard foreward (Adjust with changes in magnetic latitude) binnacle. starboard. aft intercardinal and port aft If compass north is attracted to high side of ship when rolling, raise positions. intercardinal the heeling magnet if red end is up and lower the heeling magnet if blue positions. end is up. Athwartship Raise magnets. Lower magnets. Spheres at Slew spheres Slew spheres If compass north is attracted to low side of ship when rolling, lower magnets red athwartship clockwise through counter-clockwise the heeling magnet if red end is up and raise the heeling magnet if blue starboard. position. required angle. through required end is up. angle. NOTE: Any change in placement of the heeling magnet will affect the Athwartship Lower magnets. Raise magnets. Spheres at fore and Slew spheres counter- Slew spheres deviations on all headings. magnets red port. aft position. clockwise through clockwise through required angle. required angle. Figure 601. Mechanics of magnetic compass adjustment. gyro error by sun’s azimuth or ranges on each heading to half of any observed deviation by moving the ensure a greater degree of accuracy (section 631). Be sure C magnets. gyro is set for the mean speed and latitude of the vessel. The cardinal heading adjustments should now be Note all precautions in section A-4 above. Fly the “OSCAR complete. QUEBEC” international code signal to indicate such work 6. Come to any intercardinal magnetic heading, e.g., is in progress. Section 631 discusses methods for placing northeast (045°). Correct any observed deviation the ship on desired headings. by moving the spheres in or out. 7. Come to the next intercardinal magnetic heading, 1. Adjust the heeling magnet while the ship is rolling e.g., southeast (135°). Correct half of any ob- on north and south magnetic headings until the os- served deviation by moving the spheres. cillations of the compass card have been reduced to an average minimum. This step is not required The intercardinal heading adjustments should now be if prior adjustment has been made using a dip nee- complete, although more accurate results might be ob- dle to indicate proper placement of the heeling tained by correcting the D error determined from the magnet. deviations on all four intercardinal headings, as discussed 2. Come to a cardinal magnetic heading, e.g., east in section 615. (090°). Insert fore-and-aft B magnets, or move the existing B magnets, to remove all deviation. 8. Secure all correctors before swinging for residual 3. Come to a south (180°) magnetic heading. Insert deviations. athwartship C magnets, or move the existing 9. Swing for residual undegaussed deviations on as C magnets, to remove all deviation. many headings as desired, although the eight car- 4. Come to a west (270°) magnetic heading. Correct dinal and intercardinal headings should be half of any observed deviation by moving the sufficient. B magnets. 10. Should there still be any large deviations, analyze 5. Come to a north (000°) magnetic heading. Correct the deviation curve to determine the necessary MAGNETIC COMPASS ADJUSTMENT 83 corrections and repeat as necessary steps 1 the unlike poles will attract each other. through 9 above. Magnetism can be either permanent or induced.A 11. Record deviations and the details of corrector positions bar having permanent magnetism will retain its magnetism on the deviation card to be posted near the compass. when it is removed from the magnetizing field. A bar hav- 12. Swing for residual degaussed deviations with the ing induced magnetism will lose its magnetism when degaussing circuits properly energized. removed from the magnetizing field. Whether or not a bar 13. Record deviations for degaussed conditions on the will retain its magnetism on removal from the magnetizing deviation card. field will depend on the strength of that field, the degree of hardness of the iron (retentivity), and also upon the amount The above check-off list describes a simplified method of physical stress applied to the bar while in the magnetiz- of adjusting compasses, designed to serve as a workable ing field.