《航海学》课程参考文献（地文资料）CHAPTER 06 MAGNETIC COMPASS ADJUSTMENT

CHAPTER 6MAGNETICCOMPASSADJUSTMENTGENERALPROCEDURESFORMAGNETICCOMPASSADJUSTMENT600.Introductionf.Alignment of magnets in binnacleAlignment of heeling magnet tube under pivotg.This chapter presents information and procedurespointofcompass.for magneticcompass adjustment.Sections601and613See that corrector magnets are available.hcover procedures designed to eliminate compass errorssatisfactorily.Refer toFigure 607 for condensed infor-2.Physical checks ofgyro,azimuth circle,and pelorusesAlignmentof peloruses withfore-and-aft line ofmation regardingthe various compass errors and theira.correction.ship (section610).Theterm compass adjustmentreferstoanychangeofb.Synchronize gyro repeaters with master gyro.permanent magnetorsoft iron correctorsto reducenormalc. Ensure azimuth circles and peloruses are in goodcondition.compasserrors.Thetermcompasscompensationreferstoany change inthe current slupplied to the compasscompen-3.Necessarydata.sating coils to reduce degaussing errors.a.Pasthistory or log data which might establish601.Adjustment Check-Off ListlengthofFlindersbar (sections610and623).Azimuthsfordateand observer's position (sectionb.If themagnetic adjustment necessitates (a)movement633andChapter17)of degaussing compensating coils, or (b) a change ofRanges or distant objects in vicinity if needed (lo-Ccal charts).Flinders barlength,check alsothe coil compensation persection646Correctvariation (localcharts)dExpeditiouscompass adjustmentdepends on theappli-Degaussing coil current settings forswing forresid-e.ual deviations after adjustment and compensationcation of the various correctors in an optimum sequencedesigned to minimizethe number ofcorrection steps.Cer-(ship'sDegaussingFolder).tainadjustmentsmaybe madeconveniently atdockside.4.Precautions.simplifying the at seaadjustment procedures.Determinetransient deviations of compass fromMoving thewrong correctorwastestime and upsets alla.previous adjustments,sobecareful tomakethe correctadgyrorepeaters,doors,guns,etc.(sections636and639).justments.Throughout an adjustment,special care shouldbetakentopairoff sparemagnets sothattheresultantfieldb.Secure all effective magnetic gear in normal seagoingabout them will be negligible.To make doubly sure that thepositionbeforebeginningadjustments.Make sure degaussing coils are secured before be-compass isnot affected by a sparemagnet's strayfieldCkeepthem atanappropriatedistanceuntiltheyareactuallyginning adjustments. Use reversal sequence, ifinserted into the binnacle.necessary.Whenever possible, correctors should be placedd.A.Docksidetests and adjustments.symmetricallywithrespecttothecompass.1.Physical checksonthecompassandbinnacle5.Adjustments.a.Remove any bubbles in compass bowl (sectiona.PlaceFlindersbaraccordingtobestavailableinfor-610).mation (sections 610, 622 through 625)Test for moment and sensibility of compass nee-b.b.Set spheres at mid-position, or as indicated by lastdles(section610)deviation table.Removeanyslack ingimbal arrangement.Adjust heeling magnet, using balanced dip needlec.c.dMagnetization check of spheres and Flinders barifavailable (section637).(section610)e.Alignment of compass with fore-and-aft line ofB.Adjustments at sea.Make these adjustments with the shipship (section610)on an even keel and steady on each heading. When using81

81 CHAPTER 6 MAGNETIC COMPASS ADJUSTMENT GENERAL PROCEDURES FOR MAGNETIC COMPASS ADJUSTMENT 600. Introduction This chapter presents information and procedures for magnetic compass adjustment. Sections 601 and 613 cover procedures designed to eliminate compass errors satisfactorily. Refer to Figure 607 for condensed infor￾mation regarding the various compass errors and their correction. The term compass adjustment refers to any change of permanent magnet or soft iron correctors to reduce normal compass errors. The term compass compensation refers to any change in the current slupplied to the compass compen￾sating coils to reduce degaussing errors. 601. Adjustment Check-Off List If the magnetic adjustment necessitates (a) movement of degaussing compensating coils, or (b) a change of Flinders bar length, check also the coil compensation per section 646. Expeditious compass adjustment depends on the appli￾cation of the various correctors in an optimum sequence designed to minimize the number of correction steps. Cer￾tain adjustments may be made conveniently at dockside, simplifying the at sea adjustment procedures. Moving the wrong corrector wastes time and upsets all previous adjustments, so be careful to make the correct ad￾justments. Throughout an adjustment, special care should be taken to pair off spare magnets so that the resultant field about them will be negligible. To make doubly sure that the compass is not affected by a spare magnet’s stray field, keep them at an appropriate distance until they are actually inserted into the binnacle. A. Dockside tests and adjustments. 1. Physical checks on the compass and binnacle. a. Remove any bubbles in compass bowl (section 610). b. Test for moment and sensibility of compass nee￾dles (section 610). c. Remove any slack in gimbal arrangement. d. Magnetization check of spheres and Flinders bar (section 610). e. Alignment of compass with fore-and-aft line of ship (section 610). f. Alignment of magnets in binnacle. g. Alignment of heeling magnet tube under pivot point of compass. h. See that corrector magnets are available. 2. Physical checks of gyro, azimuth circle, and peloruses. a. Alignment of peloruses with fore-and-aft line of ship (section 610). b. Synchronize gyro repeaters with master gyro. c. Ensure azimuth circles and peloruses are in good condition. 3. Necessary data. a. Past history or log data which might establish length of Flinders bar (sections 610 and 623). b. Azimuths for date and observer’s position (section 633 and Chapter 17). c. Ranges or distant objects in vicinity if needed (lo￾cal charts). d. Correct variation (local charts). e. Degaussing coil current settings for swing for resid￾ual deviations after adjustment and compensation (ship’s Degaussing Folder). 4. Precautions. a. Determine transient deviations of compass from gyro repeaters, doors, guns, etc. (sections 636 and 639). b. Secure all effective magnetic gear in normal seagoing position before beginning adjustments. c. Make sure degaussing coils are secured before be￾ginning adjustments. Use reversal sequence, if necessary. d. Whenever possible, correctors should be placed symmetrically with respect to the compass. 5. Adjustments. a. Place Flinders bar according to best available infor￾mation (sections 610, 622 through 625). b. Set spheres at mid-position, or as indicated by last deviation table. c. Adjust heeling magnet, using balanced dip needle if available (section 637). B. Adjustments at sea. Make these adjustments with the ship on an even keel and steady on each heading. When using

82MAGNETIC COMPASS ADJUSTMENTthegyro,swing slowlyfromheadingtoheading andcheckFore-and-af and athwartship magnetsQuadrantial spheresFlinders barEasterly on eastWesterly on eastE, on NEW.on NE,Deviation changeandW.onWW.onE.and E.onWDeviationDeviationE.onSE,E,onSE,andwesterly onand easterly onwith latitudewhen sailing towardwhen sailing toward2W.onw,W.onSW,west.west.changeequator fromnorth equatornorthfromandE. on NW.atitdeorawayomittudeorawayfromand>MagnetsSpheresW.onNW.(+B error)(-B error)(-D error)equatortosoutiBarequator to south latitudelatitude,(+D error)VVVNo fore and aftPlace required of bar Place required amountPlace magnets redPlace magnets redNo spheres onPlace spheresPlace spheres foreaflNo bar in holder.magnets inforward.athwartship.and aft.forward.of bar aff.binnacle.binnacle.Fore and aftRaise magnets.ower magnets.Spheres atMovespheres toward Movespheresncrease amountof barDeacrease amountmagnets redathwartshipoutwards or remove.Bar forward of binnacleforward.of bar forward.compass or useforward.position.larger spheres.Fore and aftLower magnets.Spheres at fore andMove spheresMove spheres towardDecreaseof ncrease amount ofRaise magnets.amountmagnets red af.Bar aft of binnacle.bar af.aft position.outward or remove.compass or usebar aft.larger spheresE. on N,DeviationEasterly , onnorth Westerly on northDeviationW. on E. and E. on W.EonEand W.on W.个W.onE,andwesterlyonand easterly onwhen sailing towardwhensailing towardE.ons,Barsouth.south.equator fromsouthequatorfromsouthandandlatitudeorawayfromlatitude oraway fromSpheresMagnets-C error)W.on w.E.onw.Deviation changeequator4onorthequator to south latitudeV?+C error)iatitude.(+E error)(-E error)with latitudechange->1oathwartship Placeathwartship Place asthwartshipspheresHeeling magnetnPlace spheres at pont Placespheres(Adjust with changes in magnetic latitude)magnetsinmagnetsredmagnets red porLbinnacle.forward and starboardstarbcardforewardstarboard.antbinnacle.intercardiralandaffportIf compass north is atracted to high side of ship when rolling, raiscpsitions.intercardinalheheelingmagnet if red endis up and lorertheheelingmagnet if blupositionscnd is up.AthwartshipatSlewRaise magnetsLower magnets.Spheresspheres SlewsphereIf compass north is attracted to low side of ship when rolling, loweredathuartshipmagnetsclockwisethroughcounter-clockwisehe heeling magnet if red end is up and raise the heeling magnet if blucstarboard.position,throughrequired angle.requiredend isup.angle.NOTE: Any change in placement of the heeling magnet willaffect thoAthwartshipLower magnets.Raise magnets.Spheres at fore andSlew spheres counter-Slew spheresieviations on all headings.magnets red pon.clockwise throughclockwise throughaft position.required angle.required angle.Figure601.Mechanicsofmagneticcompassadjustmenthalf of any observed deviation by moving thegyro errorby sun's azimuthor ranges on eachheadingtoCmagnets.ensurea greater degree of accuracy (section631).Be sureThe cardinal heading adjustments should now begyro is set for themean speed and latitude of the vesselNoteall precautions in sectionA-4above.Flythe“OSCARcomplete.QUEBECinternational code signaltoindicatesuchwork6.Come to any intercardinal magnetic heading, e.g.is in progress. Section 631 discusses methods for placingnortheast (045°).Correct any observed deviationtheshipondesiredheadingsby moving the spheres in or out.7.Cometo the next intercardinal magneticheading.1.Adjust the heeling magnet while the ship is rollinge.g., southeast (135).Correct half of any ob-on north and southmagnetic headings until theos-served deviationbymoving the spheres.cillations of thecompass card havebeen reducedto an averageminimum.This step is not requiredThe intercardinal heading adjustments should now beifprioradjustmenthasbeenmadeusingadipnee-completealthoughmoreaccurateresultsmightbeob-dleto indicate proper placement of theheelingtained by correctingtheD error determined from themagnet.deviations onall four intercardinal headings, as discussed2.Come to a cardinal magnetic heading, e.g., eastin section615.(090°).Insertfore-and-aftBmagnets,ormovetheexistingBmagnets,toremoveall deviation.8.Secure all correctors before swinging for residual3.Come to a south (180°) magnetic heading. Insertdeviations.9.Swing for residual undegaussed deviations on asathwartship C magnets,or move the existingCmagnets, to removeall deviation.many headings as desired, although the eight car-4.Cometo a west(270°)magnetic heading.Correctdinal and intercardinal headings shouldbehalf of any observed deviation by moving thesufficient.Bmagnets.10.Should there still be any largedeviations,analyze5.Come to a north (00o°)magnetic heading.Correctthe deviation curve to determine the necessary

82 MAGNETIC COMPASS ADJUSTMENT the gyro, swing slowly from heading to heading and check gyro error by sun’s azimuth or ranges on each heading to ensure a greater degree of accuracy (section 631). Be sure gyro is set for the mean speed and latitude of the vessel. Note all precautions in section A-4 above. Fly the “OSCAR QUEBEC” international code signal to indicate such work is in progress. Section 631 discusses methods for placing the ship on desired headings. 1. Adjust the heeling magnet while the ship is rolling on north and south magnetic headings until the os￾cillations of the compass card have been reduced to an average minimum. This step is not required if prior adjustment has been made using a dip nee￾dle to indicate proper placement of the heeling magnet. 2. Come to a cardinal magnetic heading, e.g., east (090°). Insert fore-and-aft B magnets, or move the existing B magnets, to remove all deviation. 3. Come to a south (180°) magnetic heading. Insert athwartship C magnets, or move the existing C magnets, to remove all deviation. 4. Come to a west (270°) magnetic heading. Correct half of any observed deviation by moving the B magnets. 5. Come to a north (000°) magnetic heading. Correct half of any observed deviation by moving the C magnets. The cardinal heading adjustments should now be complete. 6. Come to any intercardinal magnetic heading, e.g., northeast (045°). Correct any observed deviation by moving the spheres in or out. 7. Come to the next intercardinal magnetic heading, e.g., southeast (135°). Correct half of any ob￾served deviation by moving the spheres. The intercardinal heading adjustments should now be complete, although more accurate results might be ob￾tained by correcting the D error determined from the deviations on all four intercardinal headings, as discussed in section 615. 8. Secure all correctors before swinging for residual deviations. 9. Swing for residual undegaussed deviations on as many headings as desired, although the eight car￾dinal and intercardinal headings should be sufficient. 10. Should there still be any large deviations, analyze the deviation curve to determine the necessary Fore-and-aft and athwartship magnets Quadrantial spheres Flinders bar Deviation Magnets Easterly on east and westerly on west. (+B error) Westerly on east and easterly on west. (-B error) Deviation Spheres E. on NE, E. on SE, W. on SW, and W. on NW. (+D error) W. on NE, E. on SE, W. on SW, andE. on NW. (-D error) Deviation change with latitude change Bar E. on E. and W. on W when sailing toward equator from north latitude or away from equator to south latitude. W. on E. and E. on W when sailing toward equator from north latitude or away from equator to south latitude. No fore and aft magnets in binnacle. Place magnets red forward. Place magnets red aft. No spheres on binnacle. Place spheres athwartship. Place spheres fore and aft. No bar in holder. Place required of bar forward. Place required amount of bar aft. Fore and aft magnets red forward. Raise magnets. Lower magnets. Spheres at athwartship position. Move spheres toward compass or use larger spheres. Move spheres outwards or remove. Bar forward of binnacle. Increase amount of bar forward. Deacrease amount of bar forward. Fore and aft magnets red aft. Lower magnets. Raise magnets. Spheres at fore and aft position. Move spheres outward or remove. Move spheres toward compass or use larger spheres. Bar aft of binnacle. Decrease amount of bar aft. Increase amount of bar aft. Deviation Magnets Easterly on north and westerly on south. (+C error) Westerly on north and easterly on south. (-C error) Deviation Spheres E. on N, W. on E, E. on S, and W. on W. (+E error) W. on N, E. on E, W. on S, and E. on W. (-E error) Bar Deviation change with latitude change W. on E. and E. on W. when sailing toward equator from south latitude or away from equator to north latitude. E. on E. and W. on W. when sailing toward equator from south latitude or away from equator to south latitude No athwartship magnets in binnacle. Place athwartship magnets red starboard. Place athwartship magnets red port. No spheres on binnacle. Place spheres at port forward and starboard aft intercardinal positions. Place spheres at starboard foreward and port aft intercardinal positions. Heeling magnet (Adjust with changes in magnetic latitude) If compass north is attracted to high side of ship when rolling, raise the heeling magnet if red end is up and lower the heeling magnet if blue end is up. Athwartship magnets red starboard. Raise magnets. Lower magnets. Spheres at athwartship position. Slew spheres clockwise through required angle. Slew spheres counter-clockwise through required angle. If compass north is attracted to low side of ship when rolling, lower the heeling magnet if red end is up and raise the heeling magnet if blue end is up. NOTE: Any change in placement of the heeling magnet will affect the deviations on all headings. Athwartship magnets red port. Lower magnets. Raise magnets. Spheres at fore and aft position. Slew spheres counter￾clockwise through required angle. Slew spheres clockwise through required angle. Figure 601. Mechanics of magnetic compass adjustment

83MAGNETICCOMPASSADJUSTMENTcorrections and repeat as necessary steps 1the unlike poles will attract each other.through 9 above.Magnetism can be either permanent or induced.A11.Recorddeviations andthedetailsofcorrectorpositionsbarhavingpermanentmagnetismwill retain itsmagnetismonthedeviationcardtobepostednearthecompasswhen it is removed from themagnetizing field.A bar hav-12.Swingforresidual degausseddeviations withtheing induced magnetism will lose its magnetismwhendegaussing circuits properly energized.removed from themagnetizing field.Whetherornotabar13.Recorddeviationsfordegaussed conditions onthewill retain itsmagnetism on removal fromthemagnetizingdeviation card.field will depend on the strength ofthat field, thedegree ofhardness of the iron(retentivity),andalsoupontheamountTheabovecheck-off listdescribes a simplified methodof physical stress applied to the bar while in the magnetiz-of adjusting compasses,designed to serveas a workableing field. The harder the iron, the more permanent will beoutlineforthenovice who choosestofollowa step-by-stepthe magnetism acquired.procedure. The dockside tests and adjustments are essentialas a foundation for the adjustments at sea.Neglecting the603.Terrestrial Magnetismdocksideprocedures may lead to spurious results or need-less repetition of the procedures at sea. Give carefulConsider the earth as a huge magnet surrounded byconsideration to thesedockside checks priorto making themagnetic flux lines connecting its two magnetic poles.final adjustment.This will allowtimeto repair orreplaceThese magnetic poles are near, but not coincidental withfaulty compasses,anneal or replacemagnetized spheresorthe earth'sgeographicpoles.Since the north seekingend ofFlindersbars,realign thebinnacle,moveagyro repeater ifa compass needle is conventionally called the north pole,it isaffectingthecompass, ortomakeanyothernecessaryor positive pole, it must therefore be attracted to a southpreliminaryrepairspole, or negative pole.Expeditious compassadjustmentdependsupontheap-Figure 603a illustrates the earth and its surrounding magplicationofthevariouscorrectorsinalogicalsequencesonetic field. The flux lines enter the surface of the earth atasto achievethefinal adjustmentwithaminimum numberof steps.Theabove check-off list accomplishes thispur-different angles to the horizontal, at different magnetic ati-pose.Figure607presents thevarious compass errors andtudes. This angle is called the angle of magnetic dip, e, andtheircorrection incondensedform.Frequent, carefulobser-vations should be made to determine theconstancy ofdeviations,andresultsshouldbesvstematicallyrecordedSignificant changes in deviation will indicate the need forreadjustment.NoruTo avoid Gaussin error (section 636) when adjustingGerahand swinging shipfor residuals,the ship should be steadyPolBleon thedesiredheadingforatleast2minutespriortoobserv-Magneticing thedeviation.Polc602.The Magnetic Compass And MagnetismTheprinciple of thepresentdaymagnetic compass isnodifferentfromthatofthecompassesusedbyancientmariners.It consists of amagnetized needle,or an array ofneedles,allowed torotatein thehorizontal plane.The supe-riority of the present day compasses over ancient onesMasresultsfroma betterknowledge ofthelaws ofmagnetismwhichgovernthebehavior ofthecompass andfromgreaterprecision in construction.Any piece of metal on becoming magnetized will de-velopregionsofconcentratedmagnetismcalledpoles.AnyRedSouthsuchmagnetwill haveatleast twopoles ofoppositepolar-MagneticGeographiePoleity.Magneticforce (flux) lines connectonepoleof suchaPolemagnet with the other pole.The number of such lines perunit area represents the intensity of the magnetic field inthat area.If two such magnetic bars or magnets are placedFigure 603a.Terrestrial magnetism.close to each other,the likepoles will repel each otherand

MAGNETIC COMPASS ADJUSTMENT 83 corrections and repeat as necessary steps 1 through 9 above. 11. Record deviations and the details of corrector positions on the deviation card to be posted near the compass. 12. Swing for residual degaussed deviations with the degaussing circuits properly energized. 13. Record deviations for degaussed conditions on the deviation card. The above check-off list describes a simplified method of adjusting compasses, designed to serve as a workable outline for the novice who chooses to follow a step-by-step procedure. The dockside tests and adjustments are essential as a foundation for the adjustments at sea. Neglecting the dockside procedures may lead to spurious results or need￾less repetition of the procedures at sea. Give careful consideration to these dockside checks prior to making the final adjustment. This will allow time to repair or replace faulty compasses, anneal or replace magnetized spheres or Flinders bars, realign the binnacle, move a gyro repeater if it is affecting the compass, or to make any other necessary preliminary repairs. Expeditious compass adjustment depends upon the ap￾plication of the various correctors in a logical sequence so as to achieve the final adjustment with a minimum number of steps. The above check-off list accomplishes this pur￾pose. Figure 607 presents the various compass errors and their correction in condensed form. Frequent, careful obser￾vations should be made to determine the constancy of deviations, and results should be systematically recorded. Significant changes in deviation will indicate the need for readjustment. To avoid Gaussin error (section 636) when adjusting and swinging ship for residuals, the ship should be steady on the desired heading for at least 2 minutes prior to observ￾ing the deviation. 602. The Magnetic Compass And Magnetism The principle of the present day magnetic compass is no different from that of the compasses used by ancient mariners. It consists of a magnetized needle, or an array of needles, allowed to rotate in the horizontal plane. The supe￾riority of the present day compasses over ancient ones results from a better knowledge of the laws of magnetism which govern the behavior of the compass and from greater precision in construction. Any piece of metal on becoming magnetized will de￾velop regions of concentrated magnetism called poles. Any such magnet will have at least two poles of opposite polar￾ity. Magnetic force (flux) lines connect one pole of such a magnet with the other pole. The number of such lines per unit area represents the intensity of the magnetic field in that area. If two such magnetic bars or magnets are placed close to each other, the like poles will repel each other and the unlike poles will attract each other. Magnetism can be either permanent or induced. A bar having permanent magnetism will retain its magnetism when it is removed from the magnetizing field. A bar hav￾ing induced magnetism will lose its magnetism when removed from the magnetizing field. Whether or not a bar will retain its magnetism on removal from the magnetizing field will depend on the strength of that field, the degree of hardness of the iron (retentivity), and also upon the amount of physical stress applied to the bar while in the magnetiz￾ing field. The harder the iron, the more permanent will be the magnetism acquired. 603. Terrestrial Magnetism Consider the earth as a huge magnet surrounded by magnetic flux lines connecting its two magnetic poles. These magnetic poles are near, but not coincidental with, the earth’s geographic poles. Since the north seeking end of a compass needle is conventionally called the north pole, or positive pole, it must therefore be attracted to a south pole, or negative pole. Figure 603a illustrates the earth and its surrounding mag￾netic field. The flux lines enter the surface of the earth at different angles to the horizontal, at different magnetic ati￾tudes. This angle is called the angle of magnetic dip, θ, and Figure 603a. Terrestrial magnetism

84MAGNETICCOMPASSADJUSTMENTFigure603b.Magneticdipchart,asimplificationofchart30Figure603c.Magneticvariation chart,a simplificationof chart42

84 MAGNETIC COMPASS ADJUSTMENT Figure 603b. Magnetic dip chart, a simplification of chart 30. Figure 603c. Magnetic variation chart, a simplification of chart 42

85MAGNETICCOMPASSADJUSTMENTincreasesfrom0°,atthemagnetic equator,to90°atthemagAship,then,hasa combinationofpermanent,subperma-netic poles. The total magnetic field is generally considered asnent, and induced magnetism. Therefore, the ship's apparenthavingtwocomponents:H,thehorizontal component,andZ,permanent magnetic condition is subjecttochangefrom dep-erming,excessive shocks,welding,andvibration.Theshipstheverticalcomponent.Thesecomponentschangeastheanglee, changes, such that H is maximum at the magnetic equatorinduced magnetism will vary with the earth's magnetic fieldand decreases in the direction of eitherpole,Z is zero at theStrength and with the alignment of the ship in that field.magneticeguatorandincreasesinthedirectionofeitherpoleThevaluesofmagneticdipmaybefoundonChart30(shown605.MagneticAdjustmentsimplified inFigure603b).The values of H and Z maybefoundoncharts33and36A rod of soft iron,in aplane parallel to the earth'shor-Sincethe magnetic poles of the earth do not coincideizontal magnetic field, H, will have a north pole induced inwith thegeographic poles,a compassneedle in linewith thethe end toward the north geographic pole and a south poleearth's magnetic field will not indicatetrue north, but maginduced in the end toward the south geographic pole.Thisnetic north.The angular difference between thetrue meridiansamerod in a horizontal plane, but at right angles to the hor-(greatcircleconnectingthegeographicpoles)andthemagizontalearth'sfield,wouldhavenomagnetisminducedinitnetic meridian (direction of the lines of magnetic flux)isbecause its alignment in the magnetic field is such that therecalled variation.This variation has different values at differ-will benotendencytoward linear magnetization,and the rodentlocationsontheearth.Thesevaluesofmagneticvariationisofnegligiblecrosssection.ShouldtherodbealignedinmaybefoundonChart42(shownsimplified inFigure603c)some horizontal direction between those headings whichon pilot charts,and,on thecompass rose of navigationalcreatemaximum and zero induction,it would be induced bycharts.Thevariationformostgivenareasundergoesanan-anamountwhichisafunctionoftheangleofalignment.Ifnual change,the amount of which is also noted on chartsasimilarrodisplacedinaverticalpositioninnorthernlatitudes so as to be aligned with the vertical earth's field Z, itwill have a south pole induced at the upper end and a north604.Ship'sMagnetismpole induced at the lower end.These polarities of vertical in-duced magnetization will be reversed in southern latitudes.Aship under construction or major repair will acquireThe amount of horizontal or vertical induction in suchpermanent magnetism dueto hammering and jarring whilerods,orinshipswhoseconstructioniseguivalenttocombi-sitting stationary in the earth'smagneticfield.Afterlaunch-nations of such rods,will vary with the intensity of H andingtheshipwilllosesomeofthisoriginal magnetismasaZ, heading and heel of the shipresultofvibrationandpounding invaryingmagneticfieldsThe magnetic compass must be corrected for the ves-and will eventuallyreach amoreorless stablemagneticsel's permanent and induced magnetism so that itscondition.Themagnetismwhichremains isthepermanentoperationapproximatesthatof acompletelynonmagneticmagnetism of the ship.vessel. Ship's magnetic conditions create magnetic com-The fact that a ship has permanent magnetism does notpassdeviationsandsectorsofsluggishnessandmean that itcannot also acquire induced magnetism whenunsteadiness.Deviation isdefinedasdeflectionrightor leftplaced in the earth's magnetic field. The magnetism in-ofthemagneticmeridian.Adjustingthecompassconsistsduced in any given piece of soft iron is a function of theof arranging magnetic and soft iron correctors about thefield intensity,the alignment of the soft iron in that fieldbinnacle so that their effects are equal and opposite to theand the physical properties and dimensions of the iron. Thiseffects of the magnetic material in the ship.induced magnetismmay addto,or subtractfrom,theper-The total permanent magnetic field effect at the com-manent magnetism already present in the ship, dependingpass may be broken into three components,mutually 900on how the ship is aligned in the magnetic field.The softerapart, as shown in Figure 605a.the ironthe morereadilyit will be magnetizedbytheThe vertical permanent component tilts the compassearth's magnetic field, and the more readily it will give upcard, and, when the shiprolls or pitches, causes oscillatingitsmagnetism when removedfromthatfield.deflections of thecard.Oscillation effectswhichaccompa-Themagnetism in thevarious structures of a shipnyroll aremaximumonnorthand southcompass headingswhich tends to change as a result of cruising,vibration, orandthosewhichaccompanypitcharemaximumon eastandaging,but which does not alter immediately so asto bewestcompassheadingsproperly termed induced magnetism, is called subperma-ThehorizontalBandCcomponentsofpermanentmagnent magnetism.This magnetism, at any instant, is part ofnetism cause varying deviations of the compass as the shiptheship'spermanentmagnetism,and consequentlymustbeswings in heading on an even keel.Plotting these deviationscorrected by permanent magnet correctors.It is theprinci-against compass heading yields the sine and cosine curvespal cause of deviation changes on a magnetic compass.shown in Figure 605b.These deviation curves are calledSubsequentreferencetopermanentmagnetism will refertosemicircular curves because they reverse direction by180°theapparentpermanent magnetism which includes the ex-istingpermanentand subpermanentmagnetism.A vector analysis is helpful indetermining deviations or

MAGNETIC COMPASS ADJUSTMENT 85 increases from 0°, at the magnetic equator, to 90° at the mag￾netic poles. The total magnetic field is generally considered as having two components: H, the horizontal component; and Z, the vertical component. These components change as the angle θ, changes, such that H is maximum at the magnetic equator and decreases in the direction of either pole; Z is zero at the magnetic equator and increases in the direction of either pole. The values of magnetic dip may be found on Chart 30 (shown simplified in Figure 603b). The values of H and Z may be found on charts 33 and 36. Since the magnetic poles of the earth do not coincide with the geographic poles, a compass needle in line with the earth’s magnetic field will not indicate true north, but mag￾netic north. The angular difference between the true meridian (great circle connecting the geographic poles) and the mag￾netic meridian (direction of the lines of magnetic flux) is called variation. This variation has different values at differ￾ent locations on the earth. These values of magnetic variation may be found on Chart 42 (shown simplified in Figure 603c), on pilot charts, and, on the compass rose of navigational charts. The variation for most given areas undergoes an an￾nual change, the amount of which is also noted on charts. 604. Ship’s Magnetism A ship under construction or major repair will acquire permanent magnetism due to hammering and jarring while sitting stationary in the earth’s magnetic field. After launch￾ing, the ship will lose some of this original magnetism as a result of vibration and pounding in varying magnetic fields, and will eventually reach a more or less stable magnetic condition. The magnetism which remains is the permanent magnetism of the ship. The fact that a ship has permanent magnetism does not mean that it cannot also acquire induced magnetism when placed in the earth’s magnetic field. The magnetism in￾duced in any given piece of soft iron is a function of the field intensity, the alignment of the soft iron in that field, and the physical properties and dimensions of the iron. This induced magnetism may add to, or subtract from, the per￾manent magnetism already present in the ship, depending on how the ship is aligned in the magnetic field. The softer the iron, the more readily it will be magnetized by the earth’s magnetic field, and the more readily it will give up its magnetism when removed from that field. The magnetism in the various structures of a ship, which tends to change as a result of cruising, vibration, or aging, but which does not alter immediately so as to be properly termed induced magnetism, is called subperma￾nent magnetism. This magnetism, at any instant, is part of the ship’s permanent magnetism, and consequently must be corrected by permanent magnet correctors. It is the princi￾pal cause of deviation changes on a magnetic compass. Subsequent reference to permanent magnetism will refer to the apparent permanent magnetism which includes the ex￾isting permanent and subpermanent magnetism. A ship, then, has a combination of permanent, subperma￾nent, and induced magnetism. Therefore, the ship’s apparent permanent magnetic condition is subject to change from dep￾erming, excessive shocks, welding, and vibration. The ship’s induced magnetism will vary with the earth’s magnetic field strength and with the alignment of the ship in that field. 605. Magnetic Adjustment A rod of soft iron, in a plane parallel to the earth’s hor￾izontal magnetic field, H, will have a north pole induced in the end toward the north geographic pole and a south pole induced in the end toward the south geographic pole. This same rod in a horizontal plane, but at right angles to the hor￾izontal earth’s field, would have no magnetism induced in it, because its alignment in the magnetic field is such that there will be no tendency toward linear magnetization, and the rod is of negligible cross section. Should the rod be aligned in some horizontal direction between those headings which create maximum and zero induction, it would be induced by an amount which is a function of the angle of alignment. If a similar rod is placed in a vertical position in northern lati￾tudes so as to be aligned with the vertical earth’s field Z, it will have a south pole induced at the upper end and a north pole induced at the lower end. These polarities of vertical in￾duced magnetization will be reversed in southern latitudes. The amount of horizontal or vertical induction in such rods, or in ships whose construction is equivalent to combi￾nations of such rods, will vary with the intensity of H and Z, heading and heel of the ship. The magnetic compass must be corrected for the ves￾sel’s permanent and induced magnetism so that its operation approximates that of a completely nonmagnetic vessel. Ship’s magnetic conditions create magnetic com￾pass deviations and sectors of sluggishness and unsteadiness. Deviation is defined as deflection right or left of the magnetic meridian. Adjusting the compass consists of arranging magnetic and soft iron correctors about the binnacle so that their effects are equal and opposite to the effects of the magnetic material in the ship. The total permanent magnetic field effect at the com￾pass may be broken into three components, mutually 90° apart, as shown in Figure 605a. The vertical permanent component tilts the compass card, and, when the ship rolls or pitches, causes oscillating deflections of the card. Oscillation effects which accompa￾ny roll are maximum on north and south compass headings, and those which accompany pitch are maximum on east and west compass headings. The horizontal B and C components of permanent mag￾netism cause varying deviations of the compass as the ship swings in heading on an even keel. Plotting these deviations against compass heading yields the sine and cosine curves shown in Figure 605b. These deviation curves are called semicircular curves because they reverse direction by 180°. A vector analysis is helpful in determining deviations or

86MAGNETICCOMPASSADJUSTMENTFore-and-aft BComponent7AthwartshipCComponentCompassTotal PermanentMagneticVertical HeelingFieldAcross CompassComponentFigure 605a. Components of permanent magnetic field.the strength of deviating fields.For example, a ship aswould bemaximum on a northheadingand minimum onashown inFigure 605c on aneastmagnetic heading will sub-southheading because thedeviationsforboth conditions areject its compass to a combination of magnetic effects;zero.namely, the earth's horizontal field H, and the deviatingThe magnitude of the deviation caused by the perma-field B, at right angles to the field H. The compass needlenent B magnetic field will vary with different values of H:will align itself in the resultantfield which is represented byhence,deviationsresultingfrom permanent magneticfieldsthe vector sum ofHand B, as shown.A similar analysis willwill varywith themagnetic latitude of the ship.reveal that the resulting directive force on the compassAthwartshipPermanentEASTMagnetic CDeviations(4)Deg.Dev.7360*0200Fore-and-aftPermanentWESTMagnetic BDeviations()Ship'sCompassHeading-DegreesFigure605b.Permanent magneticdeviation effects

86 MAGNETIC COMPASS ADJUSTMENT the strength of deviating fields. For example, a ship as shown in Figure 605c on an east magnetic heading will sub￾ject its compass to a combination of magnetic effects; namely, the earth’s horizontal field H, and the deviating field B, at right angles to the field H. The compass needle will align itself in the resultant field which is represented by the vector sum of H and B, as shown. A similar analysis will reveal that the resulting directive force on the compass would be maximum on a north heading and minimum on a south heading because the deviations for both conditions are zero. The magnitude of the deviation caused by the perma￾nent B magnetic field will vary with different values of H; hence, deviations resulting from permanent magnetic fields will vary with the magnetic latitude of the ship. Figure 605a. Components of permanent magnetic field. Figure 605b. Permanent magnetic deviation effects

87MAGNETICCOMPASSADJUSTMENTrounding field, the mass ofmetal,and the alignmentofthe metalin the field. Since the intensity of the earth's magnetic field var-Resultant Ficld inies over the earth's surface, the induced magnetism in a ship willMagnitude (Directive Force)and Direction (Deviation)vary with latitude, heading, and heel of the ship.Withtheshiponanevenkeel,theresultant vertical induced-larth'sFicldmagnetism, if notdirected throughthe compass itself, will createAHdeviations which plot as a semicircular deviation curve. This is1truebecausethevertical induction changes magnitudeand po-1larity only with magnetic latitude and heel, and not with headingIdofthe ship.Therefore, as long as the ship is in the samemagnetic1latitude, its vertical induced pole swinging about the compasswill produce the sameeffect on thecompass as apermanent poleEastswinging about thecompass.MagneticHeadingThe earth's field induction in certain other unsymmetricalarrangementsof horizontal soft ironcreatea constantAdevia-tion curve. In addition to this magnetic A error, there areDeviating FieldBconstant A deviations resulting from: (I) physical misalign-Compass Needlements ofthe compass, pelorus, or gyro; (2) errors in calculatingthe sun's azimuth,observing time, or taking bearings.Figure605c.General force diagram.The nature, magnitude, and polarity of all these in-606.Induced MagnetismAnd Its Effects OnTheduced effects are dependent upon the disposition of metal,Compassthe symmetry or asymmetry of the ship,the locationof thebinnacle, the strength of the earth's magnetic field, and theInduced magnetism varies with the strength of the surangle of dip.CompassMagnetic or compassType deviationheadings ofCoefficientCauses of such errorsCorrectors for such errorsheadings on which tocurvemaximumapply corectorsdeviationCheck methods and calculations_ Human-error in calculations-.--.Check alignments4Constant.Same on all.Physicalompass, gyro,pelous alignmntAnyRare arrangement ofsoftironrodsMagnetic-unsymmetrical arrangements of horiz. soft ironFore-and-aft B magnctsSemicircularFore-and-aft component of permanent magnetic ficld_090*BInduced magnetism in unsymmetrical vertical iron forward orFlinders bar (forward or af)090°or270sing.270*aft of compassAthwartship C magnetsSemicircularAthwartship component of permanent magnetic field-000*cFlinders bar (port or starboard)000°or 180°Induced magnetism in unsymmetrical vertical iron port ocOsO.180*starboard of compass.Spheres on appropriate axisQuadrantralInduced magnetism in all symmetrical arrangements of(athwartship for +D)Dsin20225*045′,135,225′,or 315borizontal soft iron.(fore and aft for -D)315See skeicha000*Spheres on appropriate axis.QuadrantralInduced magnetism in all unsymmetrical arrangements ol(port fwd.-stb'd for +E)Ecos20.(stb'd fwdportaf for-E)0009080,or 2horizontal soft iron.270°See skeichb000Change in the horizontal component of the induced or permanenttHeling magnet (must be readjusted for090° or 270 with dip needle.Oseillations with roll roll180or pitchmagnetice fieldsat the compass due torolling or pitching ofthelatitude changes).000°or 180° while rlling.HeelingDeviatiors with090*j piteship.constant list.270°hDeviation = A + Bsin + Ccos+ Dsin20 +Ecos2(=compass heading）000+D(Santchb)(8bde)0Figure 607. Summary of compass errors and adjustments

MAGNETIC COMPASS ADJUSTMENT 87 606. Induced Magnetism And Its Effects On The Compass Induced magnetism varies with the strength of the sur￾rounding field, the mass of metal, and the alignment of the metal in the field. Since the intensity of the earth’s magnetic field var￾ies over the earth’s surface, the induced magnetism in a ship will vary with latitude, heading, and heel of the ship. With the ship on an even keel, the resultant vertical induced magnetism, if not directed through the compass itself, will create deviations which plot as a semicircular deviation curve. This is true because the vertical induction changes magnitude and po￾larity only with magnetic latitude and heel, and not with heading of the ship. Therefore, as long as the ship is in the same magnetic latitude, its vertical induced pole swinging about the compass will produce the same effect on the compass as a permanent pole swinging about the compass. The earth’s field induction in certain other unsymmetrical arrangements of horizontal soft iron create a constant A devia￾tion curve. In addition to this magnetic A error, there are constant A deviations resulting from: (1) physical misalign￾ments of the compass, pelorus, or gyro; (2) errors in calculating the sun’s azimuth, observing time, or taking bearings. The nature, magnitude, and polarity of all these in￾duced effects are dependent upon the disposition of metal, the symmetry or asymmetry of the ship, the location of the binnacle, the strength of the earth’s magnetic field, and the angle of dip. Figure 605c. General force diagram. Coefficient Type deviation curve Compass headings of maximum deviation Causes of such errors Correctors for such errors Magnetic or compass headings on which to apply correctors A Constant. Same on all. Human-error in calculations _ _ _ _ _ _ _ _ _ _ _ _ Physical-compass, gyro, pelorus alignment _ _ _ _ _ _ _ Magnetic-unsymmetrical arrangements of horiz. soft iron. Check methods and calculations _ _ _ Check alignments _ _ _ _ _ _ _ _ Rare arrangement of soft iron rods. Any. B Semicircular 090˚ 270˚ Fore-and-aft component of permanent magnetic field_ _ _ Induced magnetism in unsymmetrical vertical iron forward or aft of compass. Fore-and-aft B magnets _ _ _ _ _ _ Flinders bar (forward or aft) _ _ _ _ 090˚ or 270˚. C Semicircular 000˚ 180˚ Athwartship component of permanent magnetic field- - - Induced magnetism in unsymmetrical vertical iron port or starboard of compass. Athwartship C magnets _ _ _ _ _ _ Flinders bar (port or starboard) _ _ _ 000˚ or 180˚. D Quadrantral 045˚ 135˚ 225˚ 315˚ Induced magnetism in all symmetrical arrangements of horizontal soft iron. Spheres on appropriate axis. (athwartship for +D) (fore and aft for -D) See sketch a 045˚, 135˚, 225˚, or 315˚. E Quadrantral 000˚ 090˚ 180˚ 270˚ Induced magnetism in all unsymmetrical arrangements of horizontal soft iron. Spheres on appropriate axis. (port fwd.-stb’d for +E) (stb’d fwd.-port aft for -E) See sketch b 000˚, 090˚, 180˚, or 270˚. Heeling Oscillations with roll or pitch. Deviations with constant list. 000˚ 180˚ 090˚ 270˚ }roll }pitc h Change in the horizontal component of the induced or permanent magnetic fields at the compass due to rolling or pitching of the ship. Heeling magnet (must be readjusted for latitude changes). 090˚ or 270˚ with dip needle. 000˚ or 180˚ while rolling. Figure 607. Summary of compass errors and adjustments. sin . φ cos . φ sin2φ . cos2φ . Deviation = 2 A B + sinφ + C cosφ + D sin φ + E cos2φ φ( ) = compass heading

88MAGNETICCOMPASS ADJUSTMENTCertain heeling errors, in addition to those resultingvertical tubefrom permanent magnetism,are created by the presence of2.Fore-and-af B permanent magnets in their trays.both horizontal and vertical soft iron which experience3.AthwartshipCpermanentmagnets in theirtrays.changinginductionastheshiprollsintheearth'smagnetic4.Vertical soft ironFlinders bar in its external tube.5. Soft iron quadrantal spheres.field.This part of the heeling error will naturally change inmagnitude with changes of magnetic latitude of the ship.Oscillationeffectsaccompanyingroll aremaximum onThe heelingmagnet is the only corrector which cornorth and south headings, just as with the permanent magrects for both permanent and induced effects.Therefore,itnetic heelingerrors.mustbeadjusted occasionallyforchanges inship's latitudeHowever,anymovement of theheelingmagnetwill require607.AdjustmentsAnd Correctorsreadjustmentofothercorrectors.Figure607summarizes all thevarious magneticcondi-Since some magnetic effects are functions of the ves-tions in a ship,thetypes ofdeviation curvestheycreate,thesel'smagneticlatitudeandothersarenoteachindividualcorrectors for each effect,and headings on which each cor-effectshould becorrected independently.Furthermore,torector is adjusted.Applythecorrectors symmetricallyandas far awayfrom the compass as possible.This preservesmakethecorrections,use(1)permanent magnet correctorsto compensateforpermanentmagneticfieldsatthecom-theuniformityofmagneticfields aboutthecompassneedlepass,and(2)soft ironcorrectorsto compensatefor inducedarray.Fortunately, each magnetic effect has a slightly differ-magnetism.The compassbinnacleprovides support forboththe compass and such correctors.Typical binnaclesent characteristic curve.This makes identification andholdthefollowing correctors:correction convenient.Analyzing a complete deviationcurve for its different components allows one to anticipate1.Vertical permanent heeling magnet in the centralthe necessary corrections.COMPASSOPERATION608.EffectsOfErrorsOnTheCompassple,ashipwhosecompassisfrozentoanorthreadingwouldrequirefore-and-afftBcorrectormagnetswiththepositiveAn uncorrected compass suffers largedeviations andends forward in order to neutralize the existing negative polesluggish,unsteady operation.These conditions may be as-which attracted the compass.If made on an east heading,sociatedwiththemaximumandminimumdirectiveforcesuch an adjustment would bepractically complete when theacting onthe compass.Themaximum deviation occurs atcompasscardwasfreedto indicatean eastheading.the point ofaveragedirective force;andthe zero deviationsoccuratthepointsofmaximumandminimumdirective609.ReasonsForCorrectingCompassforce.Applying correctors to reduce compass deviation ef-There are several reasons for correcting the errors offects compass error correction. Applying correctors tothemagnetic compass:equalizethe directiveforces acrossthecompass position1.It is easierto useamagnetic compass if the devia-couldalsoeffectcompasscorrection.Thedeviationmethodis most often used because it utilizes the compass itself astions are small.the correction indicator.Equalizing the directive forces2.Evenknownandcompensatedfordeviationintro-would require an additional piece of test and calibrationduceserrorbecausethe compass operatesequipment.Occasionally,thepermanentmagnetic effects atthelo-sluggishly and unsteadilywhen deviation iscation ofthe compass are so largethattheyovercomethepresent.earth's directiveforce,H.This condition will not only create3.Even thoughthedeviations are compensated for.sluggish and unsteady sectors,but mayevenfreeze the com-pass to one reading or to one quadrant, regardless of thethey will be subject to appreciablechange as aheading ofthe ship.Should the compass become sofrozen,function ofheel and magnetic latitude.the polarity of the magnetism which must be attracting thecompass needles is indicated;hence, correction may be efOnce properly adjusted,themagnetic compass devia-fected simply by the application of permanent magnettions should remain constant until there is some change incorrectors, in suitable quantity to neutralize this magnetism.themagneticconditionofthevessel resultingfrommagneticWhenever such adjustments aremade,it would bewell totreatment,shockfromgunfire,vibration,repair,orstructuralhavetheshipplacedon aheading suchthattheunfreezingofchanges.Frequently,the movement of nearbyguns, doors,thecompassneedleswill be immediately evident.For exam-gyrorepeaters,orcargo affectsthecompassgreatly

88 MAGNETIC COMPASS ADJUSTMENT Certain heeling errors, in addition to those resulting from permanent magnetism, are created by the presence of both horizontal and vertical soft iron which experience changing induction as the ship rolls in the earth’s magnetic field. This part of the heeling error will naturally change in magnitude with changes of magnetic latitude of the ship. Oscillation effects accompanying roll are maximum on north and south headings, just as with the permanent mag￾netic heeling errors. 607. Adjustments And Correctors Since some magnetic effects are functions of the ves￾sel’s magnetic latitude and others are not, each individual effect should be corrected independently. Furthermore, to make the corrections, use (1) permanent magnet correctors to compensate for permanent magnetic fields at the com￾pass, and (2) soft iron correctors to compensate for induced magnetism. The compass binnacle provides support for both the compass and such correctors. Typical binnacles hold the following correctors: 1. Vertical permanent heeling magnet in the central vertical tube. 2. Fore-and-aft B permanent magnets in their trays. 3. Athwartship C permanent magnets in their trays. 4. Vertical soft iron Flinders bar in its external tube. 5. Soft iron quadrantal spheres. The heeling magnet is the only corrector which cor￾rects for both permanent and induced effects. Therefore, it must be adjusted occasionally for changes in ship’s latitude. However, any movement of the heeling magnet will require readjustment of other correctors. Figure 607 summarizes all the various magnetic condi￾tions in a ship, the types of deviation curves they create, the correctors for each effect, and headings on which each cor￾rector is adjusted. Apply the correctors symmetrically and as far away from the compass as possible. This preserves the uniformity of magnetic fields about the compass needle array. Fortunately, each magnetic effect has a slightly differ￾ent characteristic curve. This makes identification and correction convenient. Analyzing a complete deviation curve for its different components allows one to anticipate the necessary corrections. COMPASS OPERATION 608. Effects Of Errors On The Compass An uncorrected compass suffers large deviations and sluggish, unsteady operation. These conditions may be as￾sociated with the maximum and minimum directive force acting on the compass. The maximum deviation occurs at the point of average directive force; and the zero deviations occur at the points of maximum and minimum directive force. Applying correctors to reduce compass deviation ef￾fects compass error correction. Applying correctors to equalize the directive forces across the compass position could also effect compass correction. The deviation method is most often used because it utilizes the compass itself as the correction indicator. Equalizing the directive forces would require an additional piece of test and calibration equipment. Occasionally, the permanent magnetic effects at the lo￾cation of the compass are so large that they overcome the earth’s directive force, H. This condition will not only create sluggish and unsteady sectors, but may even freeze the com￾pass to one reading or to one quadrant, regardless of the heading of the ship. Should the compass become so frozen, the polarity of the magnetism which must be attracting the compass needles is indicated; hence, correction may be ef￾fected simply by the application of permanent magnet correctors, in suitable quantity to neutralize this magnetism. Whenever such adjustments are made, it would be well to have the ship placed on a heading such that the unfreezing of the compass needles will be immediately evident. For exam￾ple, a ship whose compass is frozen to a north reading would require fore-and-aft B corrector magnets with the positive ends forward in order to neutralize the existing negative pole which attracted the compass. If made on an east heading, such an adjustment would be practically complete when the compass card was freed to indicate an east heading. 609. Reasons For Correcting Compass There are several reasons for correcting the errors of the magnetic compass: 1. It is easier to use a magnetic compass if the devia￾tions are small. 2. Even known and compensated for deviation intro￾duces error because the compass operates sluggishly and unsteadily when deviation is present. 3. Even though the deviations are compensated for, they will be subject to appreciable change as a function of heel and magnetic latitude. Once properly adjusted, the magnetic compass devia￾tions should remain constant until there is some change in the magnetic condition of the vessel resulting from magnetic treatment, shock from gunfire, vibration, repair, or structural changes. Frequently, the movement of nearby guns, doors, gyro repeaters, or cargo affects the compass greatly

89MAGNETICCOMPASSADJUSTMENTDETAILEDPROCEDURESFORCOMPASSADJUSTMENT610.DocksideTestsAndAdjustmentssection611AdjusttheFlinders barfirst becauseit is subjecttoSection 601,theAdjustment Checkoff List,gives theinduction from several of the correctors and its adjust-physical checks required before beginning an adjustment.ment isnot dependent on any single observation.ToTheadjustment procedure assumes that thesecheckshaveadjust the Flinders bar, use one of the followingbeen completed.Thenavigatorwill avoid much delaybymethods:making these checks before starting the magnet and softiron corrector adjustments.The most important of theseI.Use deviation data obtained at two different magchecksarediscussedbelow.netic latitudes to calculatethe proper length ofFlinders bar for anyparticular compass location.Shouldthecompasshaveasmall bubble,addcompassfluidthroughthefillingplugonthecompassbowl.Ifan apSections622through624containdetailson acquir-ing thedata and making the required calculations.preciable amountof compass liquid hasleaked out, checkthe sealinggasket and filling plug for leaks.2.If the above method is impractical, set the FlindersTake the compass to a place freefrom all magnetic in-fluences except the earth's magnetic field for tests ofbar length by:momentandsensibilitv.Thesetestsinvolvemeasurementsa. Using a Flinders bar length determined byof thetimeofvibrationandtheabilityofthecompasscardto return toa consistent reading after deflection.Thesetestsother ships of similar structure.will indicate thecondition ofthe pivot, jewel, and magneticb.Studying thearrangementofmasts,stacksstrengthofthecompassneedlesand other vertical structures and estimating theNext, check the spheres and Flinders bar for residualFlinders bar length required.magnetism.Movethe spheres as close to the compass aspossible and slowly rotate each sphere separately.Any ap-Ifthese methodsarenotsuitable,omittheFlindersbarpreciabledeflection (2°ormore)of the compass needlesresultingfromthisrotationindicatesresidualmagnetisminuntil the required data are acquired.The iron sections of Flinders bar shouldbe continu-the spheres. The Flinders bar magnetization check is pref-ous and placed atthe top of thetube with the longesterablymadewith theshipon an east orwestcompasssection at the top. Wooden spacers are used at the bottomheading.Tomakethis check:(a)note thecompass readingof the tube.with the Flinders bar in the holder; (b) invert the Flindersbar in theholder and again note the compass reading.AnyHaving adjusted thelength of Flinders bar,place theappreciabledifference(2°ormore)betweentheseobservedspheres onthebracketarmsatan approximateposition.Ifthe compass has been adjusted previously,placethereadings indicates residual magnetism in theFlinders barSpheres or Flinders bars which show signs of such residualspheres at the position indicated by the previous devia-magnetism shouldbe annealed,i.e.,heated toa dull red andtion table. In the event the compass has never beenallowedtocool slowlyadjusted,place the spheres at the midpoint on thebracketCorrect alignmentof the lubber's line of thecom-arms.The next adjustment is the positioning of the heelingpass,gyro repeater, and pelorus with the fore-and-aftmagnetusinga properlybalanced dipneedle.Section637line ofthe ship is important.Any misalignment will pro-duce a constant error in the deviation curve.All of thesediscussesthisprocedureinstruments may be aligned correctly with the fore-and-These three dockside adjustments (Flinders bar, qua-aft lineof the shipbyusingtheazimuthcircle and amet-drantal spheres,and heeling magnet)will properlyestablishthe conditions of mutual induction and shielding of theal tapemeasure.Should the instrument belocated on thecompass.This minimizes the steps required at sea to com-centerline of theship, asight istakenonamastor otherobject on the centerline.If the instrument is not on theplete the adjustment.centerline, measure the distance from the centerline of611.Expected Errorsthe ship to the center of the instrument. Mark this dis-tanceoff fromthecenterlineforward orabaft thecompassandplacereferencemarks onthedeck.TakeFigure 607 lists six different coefficients or types ofde-sights on these marks.viation errors with their causes and correspondingAlignthecompass sothatthecompass'lubber'sline iscorrectors.Adiscussion ofthesecoefficientsfollows:parallel to the fore-and-aft line of the ship.Steering com-TheAerroriscausedbythemiscalculation of azimuthspasses may occasionally be deliberately misaligned in orderorbyphysical misalignments ratherthan magneticeffectsofto correctfor anymagnetic Aerror present,as discussed inunsymmetrical arrangements of horizontal soft iron.Thus

MAGNETIC COMPASS ADJUSTMENT 89 DETAILED PROCEDURES FOR COMPASS ADJUSTMENT 610. Dockside Tests And Adjustments Section 601, the Adjustment Checkoff List, gives the physical checks required before beginning an adjustment. The adjustment procedure assumes that these checks have been completed. The navigator will avoid much delay by making these checks before starting the magnet and soft iron corrector adjustments. The most important of these checks are discussed below. Should the compass have a small bubble, add compass fluid through the filling plug on the compass bowl. If an ap￾preciable amount of compass liquid has leaked out, check the sealing gasket and filling plug for leaks. Take the compass to a place free from all magnetic in￾fluences except the earth’s magnetic field for tests of moment and sensibility. These tests involve measurements of the time of vibration and the ability of the compass card to return to a consistent reading after deflection. These tests will indicate the condition of the pivot, jewel, and magnetic strength of the compass needles. Next, check the spheres and Flinders bar for residual magnetism. Move the spheres as close to the compass as possible and slowly rotate each sphere separately. Any ap￾preciable deflection (2° or more) of the compass needles resulting from this rotation indicates residual magnetism in the spheres. The Flinders bar magnetization check is pref￾erably made with the ship on an east or west compass heading. To make this check: (a) note the compass reading with the Flinders bar in the holder; (b) invert the Flinders bar in the holder and again note the compass reading. Any appreciable difference (2° or more) between these observed readings indicates residual magnetism in the Flinders bar. Spheres or Flinders bars which show signs of such residual magnetism should be annealed, i.e., heated to a dull red and allowed to cool slowly. Correct alignment of the lubber’s line of the com￾pass, gyro repeater, and pelorus with the fore-and-aft line of the ship is important. Any misalignment will pro￾duce a constant error in the deviation curve. All of these instruments may be aligned correctly with the fore-and￾aft line of the ship by using the azimuth circle and a met￾al tape measure. Should the instrument be located on the centerline of the ship, a sight is taken on a mast or other object on the centerline. If the instrument is not on the centerline, measure the distance from the centerline of the ship to the center of the instrument. Mark this dis￾tance off from the centerline forward or abaft the compass and place reference marks on the deck. Take sights on these marks. Align the compass so that the compass’ lubber’s line is parallel to the fore-and-aft line of the ship. Steering com￾passes may occasionally be deliberately misaligned in order to correct for any magnetic A error present, as discussed in section 611. Adjust the Flinders bar first because it is subject to induction from several of the correctors and its adjust￾ment is not dependent on any single observation. To adjust the Flinders bar, use one of the following methods: 1. Use deviation data obtained at two different mag￾netic latitudes to calculate the proper length of Flinders bar for any particular compass location. Sections 622 through 624 contain details on acquir￾ing the data and making the required calculations. 2. If the above method is impractical, set the Flinders bar length by: a. Using a Flinders bar length determined by other ships of similar structure. b. Studying the arrangement of masts, stacks, and other vertical structures and estimating the Flinders bar length required. If these methods are not suitable, omit the Flinders bar until the required data are acquired. The iron sections of Flinders bar should be continu￾ous and placed at the top of the tube with the longest section at the top. Wooden spacers are used at the bottom of the tube. Having adjusted the length of Flinders bar, place the spheres on the bracket arms at an approximate position. If the compass has been adjusted previously, place the spheres at the position indicated by the previous devia￾tion table. In the event the compass has never been adjusted, place the spheres at the midpoint on the bracket arms. The next adjustment is the positioning of the heeling magnet using a properly balanced dip needle. Section 637 discusses this procedure. These three dockside adjustments (Flinders bar, qua￾drantal spheres, and heeling magnet) will properly establish the conditions of mutual induction and shielding of the compass. This minimizes the steps required at sea to com￾plete the adjustment. 611. Expected Errors Figure 607 lists six different coefficients or types of de￾viation errors with their causes and corresponding correctors. A discussion of these coefficients follows: The A error is caused by the miscalculation of azimuths or by physical misalignments rather than magnetic effects of unsymmetrical arrangements of horizontal soft iron. Thus

90MAGNETICCOMPASSADJUSTMENTchecking the physical alignments at dockside and makingTheB error results fromboththefore-and-aftperma-careful calculations will minimize the A error. Where an azi-nent magnetic field across the compass and a resultantunsymmetrical vertical inducedeffectforward or aftofthemuth or bearing circle is used on a standard compass todeterminedeviations,anyobservedA errorwill be solelymagcompass.Theformer is correctedbytheuseoffore-and-aftneticAerrorbecause suchreadings aretakenon thefaceoftheB magnets, and the latter is corrected by the use of thecompass card rather than at the lubber's line of the compass.Flindersbarforward oraftof thecompass.BecausetheOna steering compasswheredeviationsareobtainedbyaFlinders bar setting is a dockside adjustment, any remainingcomparison of the compass lubber's line reading with theB error is corrected by the use of fore-and-aft Bmagnets.ship's magnetic heading,as determined by pelorus or gyro,The C error results from the athwartship permanentanyobservedAerrormaybeacombinationofmagneticAandmagnetic field across the compass and a resultant unsym-mechanicalA(misalignment).Thesefacts explaintheproce-metrical vertical induced effect athwartshipofthe compassdure in which only mechanical A is corrected on the standardTheformer is corrected bytheuse of athwartshipC magcompass,byrealignmentofthebinnacle,andbothmechanicalnets, and thelatter by the use ofthe Flinders bar to port orAandmagneticAerrors arecorrected onthesteering compassstarboard of the compass.Because the vertical induced ef-byrealignmentofthebinnacle.Onthestandardcompass,thefect is very rare,the C error is corrected by athwartshipmechanicalAerrormaybe isolatedfromthemagneticAerrorCmagnets onlyby making thefollowing observations simultaneously:TheD erroris due onlyto induction in the symmetricalarrangementsofhorizontal soft iron,andrequirescorrection1Record a curveof deviationsbyusingan azimuthbyspheres,generallyathwartshipofthecompass.(or bearing) circle. Any A error found will be solelyE error of appreciablemagnitude is rare,since it ismagnetic A.caused by induction in the unsymmetrical arrangements ofhorizontal soft iron.When this error is appreciable itmay be2.Recorda curveof deviationsbycomparisonof thecorrectedbyslewingthespheres,asdescribed in section620compass lubber's line reading with the ship's mag-As stated previously,the heeling error is adjusted atnetic heading as determined by pelorus or by gyro.docksidewith a balanced dipneedle (see section637)Any A error found will bea combination of me-As the above discussion points out, certain errors arechanical Aand magnetic Arare andothers are correctedatdockside.Therefore,formostships, only the B, C, and D errors require at sea correction.3.ThemechanicalAonthestandardcompassisthenThese errors are corrected by the fore-and-aft B magnets,found by subtracting the A found in the first in-athwartshipC magnets,andquadrantal spheres respectivelystance from the total A found in thesecondinstance,andiscorrectedbyrotatingthebinnacle612. Study OfAdjustment Procedurein the proper direction by that amount. It is neitherconvenientnornecessaryto isolate thetwotypesofInspecting the B, C, and D errors pictured in FigureA on the steering compass and all Afound by usingthe pelorus or gyro may be removed by rotating the612a demonstrates a definiteisolation ofdeviation effectsbinnacle in the proper direction.on cardinal compass headings.HEast(+)Deg.Dev.West(-)90180"270360"oCompass Heading-DegreesFigure 612a. B, C, and D deviation effects

90 MAGNETIC COMPASS ADJUSTMENT checking the physical alignments at dockside and making careful calculations will minimize the A error. Where an azi￾muth or bearing circle is used on a standard compass to determine deviations, any observed A error will be solely mag￾netic A error because such readings are taken on the face of the compass card rather than at the lubber’s line of the compass. On a steering compass where deviations are obtained by a comparison of the compass lubber’s line reading with the ship’s magnetic heading, as determined by pelorus or gyro, any observed A error may be a combination of magnetic A and mechanical A (misalignment). These facts explain the proce￾dure in which only mechanical A is corrected on the standard compass, by realignment of the binnacle, and both mechanical A and magnetic A errors are corrected on the steering compass by realignment of the binnacle. On the standard compass, the mechanical A error may be isolated from the magnetic A error by making the following observations simultaneously: 1. Record a curve of deviations by using an azimuth (or bearing) circle. Any A error found will be solely magnetic A. 2. Record a curve of deviations by comparison of the compass lubber’s line reading with the ship’s mag￾netic heading as determined by pelorus or by gyro. Any A error found will be a combination of me￾chanical A and magnetic A. 3. The mechanical A on the standard compass is then found by subtracting the A found in the first in￾stance from the total A found in the second instance, and is corrected by rotating the binnacle in the proper direction by that amount. It is neither convenient nor necessary to isolate the two types of A on the steering compass and all A found by using the pelorus or gyro may be removed by rotating the binnacle in the proper direction. The B error results from both the fore-and-aft perma￾nent magnetic field across the compass and a resultant unsymmetrical vertical induced effect forward or aft of the compass. The former is corrected by the use of fore-and-aft B magnets, and the latter is corrected by the use of the Flinders bar forward or aft of the compass. Because the Flinders bar setting is a dockside adjustment, any remaining B error is corrected by the use of fore-and-aft B magnets. The C error results from the athwartship permanent magnetic field across the compass and a resultant unsym￾metrical vertical induced effect athwartship of the compass. The former is corrected by the use of athwartship C mag￾nets, and the latter by the use of the Flinders bar to port or starboard of the compass. Because the vertical induced ef￾fect is very rare, the C error is corrected by athwartship C magnets only. The D error is due only to induction in the symmetrical arrangements of horizontal soft iron, and requires correction by spheres, generally athwartship of the compass. E error of appreciable magnitude is rare, since it is caused by induction in the unsymmetrical arrangements of horizontal soft iron. When this error is appreciable it may be corrected by slewing the spheres, as described in section 620. As stated previously, the heeling error is adjusted at dockside with a balanced dip needle (see section 637). As the above discussion points out, certain errors are rare and others are corrected at dockside. Therefore, for most ships, only the B, C, and D errors require at sea correction. These errors are corrected by the fore-and-aft B magnets, athwartship C magnets, and quadrantal spheres respectively. 612. Study Of Adjustment Procedure Inspecting the B, C, and D errors pictured in Figure 612a demonstrates a definite isolation of deviation effects on cardinal compass headings. Figure 612a. B, C, and D deviation effects