H.O 211 LINE OF POSITION WORKSHEET Section a (time) Section b (sextant) Date ____d____m______y Sextant Angle _____ø______' (SA) Watch time ____h____m____s Index Error ñ_____ø______' (IC) Corrections: Refraction -______' Chg to 24 hr____h____m____s Dip -______' Watch errorñ_________m____s Semi-diameter +______' Time zone ñ____h____m (- for upper limb) Parallax corr. +______' GMT ____h____m____s (moon only) Ho _____ø______' Section c (from almanac) Comments Declination _____ø______' d____ __________________________________ Interp. ñ______' ____________________________________ (from table) True Decl. _____ø______' ____________________________________ GHA _____ø______' ____________________________________ Interp. +_____ø______' ____________________________________ (from table) True GHA _____ø______' ____________________________________ ____________________________________ Section d (sight reduction) col I col II col III col IV col V Est Lon ñ_____ø______' (+ if Lon east of Greenwich, - if Lon west) LHA _____ø______' (if < 0ø, add 360ø) t _____ø______'->A _______ (LHA if < 180ø, else 360ø-LHA) True Decl. _____ø______'->B+_______ A _______ (from sec c) A _______ -->B-_______ B _______ A _______ K _____ø______' <-------- A _______ (if t > 90ø then K > 90ø) Est Lat ñ_____ø______' (- if decl same name as lat, + if contrary) K ñ Est Lat _____ø______' --------> B+_______ (take abs) Hc _____ø______' <------- A _______->B-_______ Ho -_____ø______' (Ho greater: toward; Hc greater: away) (from sec b) delta _____ø______' mi toward| Zn_____ø Z_____ø <--A _______ away | H.O 211 Instructions 1) Record Date and Time of sight in top 2 lines of section a 2) Record sextant data top line of in section b 3) Enter correction to time in section a 4) Sum corrections to arrive at GMT in last line of section a 5) Enter index error, refraction, and dip corrections in section b 6) Look up semi-diameter in almanac and enter in section b (sun and moon only) 7) Look up parallax correction in parallax table and enter in section b (moon only) 8) Sum corrections to arrive at Ho in last line of section b 9) Look up time and date in almanac to the nearest hour of GMT and record GHA and Declination of sighted object in section c 10)Lookup interpolation values for GHA and Declination in appropriate tables using the remainder minutes and seconds of GMT. Enter these corrections in section c 11)Sum corrections to Declination and GHA to get True Decl. and True GHA. Enter these into section c 12)Enter your estimated longitude into section d. Sum as indicated to GHA to get LHA and enter this into section d. Now carry LHA into the blank marked t in section d, doing the necessary conversion as shown to the right 13)Look up t angle in H.O. 211 table and record the A value in col II 14)Copy True Decl. from section c to section d. Look up True Decl. angle in table. Enter B value in col II and A value in col III 15)Add col II values and enter sum in blank provided in col II. Also copy the sum into col V 16)Find the sum in col II as an A value in table. Enter the associated B value into col III and col IV. If the sum falls in between two widely spaced A values in the table, it may be necessary to interpolate between the corresponding values of B. It is important that this B value be accurate. 17)Subtract B value in col III from A value in col III and enter the difference in the blank provided in col III 18)Find the difference in col III as an A value in the table. Enter the associated angle in col I in the blank marked K. Observe that if t in col I is > 90ø then use the angle K in the table that is also > 90ø. If t < 90ø, use K < 90ø 19)Enter your estimated latitude in the blank provided in col I 20)Compute the sum or difference as indicated of K angle and Est Lat. Enter the result in the blank indicated in col I. If result < 0ø, drop the sign (that is if Est Lat > K, subract K from Est Lat). 21)Look up K ñ Est Lat in the table. Enter the B value in col IV 22)Sum the two values in col IV and enter the result in the blank provided 23)Find the sum in col IV in the table as an A value. Enter the associated B value in col V and the associated angle in col I in the blank labeled Hc (Hc always < 90ø) 24)Subtract the B value in col V from the A value in col V and enter the result in the blank provided in col V 25)Find the difference in col V in the table as an A value. Enter the associated angle in the blank marked Z. Observe the following quadrant rules carefully: If t > 90ø, then always use Z < 90ø. Otherwise, if you used the sum in step 20, then always use Z > 90ø. If you used the difference in step 20, then if Est Lat < angle K, use Z > 90ø, else use Z < 90ø 26)To determine Zn: If you are in the northern hemisphere and LHA < 180ø, Zn = 360ø - Z, else Zn = Z. If you are in the southern hemisphere and LHA < 180ø, Zn = 180ø + Z, else Zn = 180ø - Z 27)Enter Ho from section b into the blank provided in col I. Enter the difference between Hc and Ho to obtain your delta miles. Enter this value in the blank provided in col I 28)Go to a plotting sheet. Your estimated position (Est Lon & Est Lat) is at the center of the compass rose. Plot an azimuth line through the center of the rose that passes through the value of Zn on the rose. This line should extend in both directions from the center of the rose. Now write the name of the object sighted along with the GMT of the sighting next to the Zn value on the rose 29)Use the scale on the vertical axis to set your dividers to the value shown as delta in col I of your worksheet 30)Use the dividers to measure that distance along the azimuth line from the center of the rose. If Ho > Hc in col I of your worksheet, measure toward the sighted object. If Ho < Hc, measure away. Mark this spot on the azimuth line 31)Draw a line of position (LOP) that passes through the point you just plotted in step 30 and is at right angles to your azimuth line. Label it as an LOP and include the name of the object sighted and the GMT of the sighting. Your position at that time is somewhere along that line 32)Sight another object, or wait a while (at least an hour) and sight the same object again. On a separate worksheet, repeat steps 1 through 27. Be SURE to use the same Est Lat and Est Lon as you did on the first worksheet. Repeat steps 28 through 31 on the same plotting sheet 33)If you have not moved significantly during the time elapsed between the two sights, your position is where the two LOPs intersect and you may skip to step 39 34)Draw a line through the center of the rose that also passes through your course heading on the rose. Extend this line so that it intersects your first LOP. 35)Find the product of your speed (in knots) and the time elapsed between sightings (in hours) 36)Use the scale on the vertical axis to set your dividers to the product arrived at in step 35 37)Use the dividers to measure that distance from the intersection point identified in step 34 along your course heading line, but in the opposited direction as your heading. Plot a point there 38)Use parallel rules to slide your FIRST LOP so that it passes through the point you plotted in step 37. Label it ADJ LOP 39)Where your second LOP intersects your ADJ LOP (of if you skipped steps 34 through 38, where your second LOP intesects your first) is where you are. How much your estimated position is in error is indicated by the distance and direction this intersection point is in relation to the center of the compass rose. Use your dividers to measure your error in latitude by setting them to the vertical distance between the center of the rose and the intersection point. Measure this along the vertical axis. Do the same horizontally to measure your error in longitude, but this time, instead of using the scale along the vertical axis, measure it using the latitude correction scale at the corner of your plotting sheet. NOTE: If you plot more than two LOPs, use the same Est Lat and Est Lon on all of the work sheets. All of the LOPs except the last must be slid the appropriate amount (computed using steps 34 through 38 but in each case using the time elapsed from the sight involved until the last sight).