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1 Plotting Celestial LOPs Junior Navigation Chapters 8 & 9 and part of Chapter 13

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2 Learning Objectives Set up a Constant Latitude Scale Small Area Plotting Sheet (CLS SAPS) Plot a single celestial LOP Plot a celestial running fix Meridian Transit of the sun Setup a Universal Plotting Sheet (UPS) – Chap 13

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Plotting Techniques Don’t rush Sharp-pointed pencil (medium/hard) Complete plot before labeling Erase unnecessary lines Errors result - working too fast - not checking plots Recheck results if they differ by more than 0.5´ on CLS Sheets. Small variations are normal

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Constant Latitude Scale Small Area Plotting Sheet Directions from Compass Rose Latitude Scale fixed, you select Mid-Lat You create the Lo scale for your area using arcs on lower part of form 1’ 3’ 5’ 7’ 9’ 2’ 4’ 6’ 8’ 1º1º

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Constant Latitude Scale Small Area Plotting Sheet Plot 1258 DR at: L 44º 50.6’ N Lo 92º 21.2’ W STEP 1 Label ‘Mid Lat’ that will allow plot to be near center of form. Label each of the 10’ increments. 30’ 45ºN 30’ 20’ 10’ 50’ 40’ 30’

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Constant Latitude Scale Small Area Plotting Sheet Plot 1258 DR at: L 44º 50.6’ N Lo 92º 21.2’ W STEP 2 Lo varies to Mid-Lat Draw diagonal lines between the bottom center & preprinted values for selected Mid-Lat 30’ 45ºN 30’ 20’ 10’ 50’ 40’ 30’ 45º

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Constant Latitude Scale Small Area Plotting Sheet Plot 1258 DR at: L 44º 50.6’ N Lo 92º 21.2’ W STEP 3 Intersections of diagonal lines and solid arcs mark locations of 10’ meridians Draw meridians Label meridians 30’ 45ºN 30’ 20’ 10’ 50’ 40’ 30’ 1º latitude 1º longitude 60nm x 60nm 92ºW50’ You are on your way in becoming a cartographer 10’30’40’50’ 20’

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45ºN 30’ 20’ 10’ 50’ 40’ 30’ 92ºW10’30’ 20’ 40’50’ Constant Latitude Scale Small Area Plotting Sheet Plot 1258 DR at: L 44º 50.6’ N Lo 92º 21.2’ W STEP 4 Plot your position 30’ 1258

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Constant Latitude Scale Small Area Plotting Sheet Plot 1258 DR at: L 44º 50.6’ N Lo 92º 21.2’ W 30’ 45ºN 30’ 20’ 10’ 50’ 40’ 30’ 92ºW10’30’ 20’ 40’50’ 1258 STEP 5 With sun intercept 4.0nm towards and azimuth 205º, plot your estimated position 1258 Sun EPL 44º 47.0’ N Lo 092º 24.5’ W

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Constant Latitude Scale Small Area Plotting Sheet 30’ 45ºN 30’ 20’ 10’ 50’ 40’ 30’ 92ºW10’30’ 20’ 40’50’ 1258 GPS 1258 Sun EPL 44º 47.0’ N Lo 092º 24.5’ W Sight reduced from FIX: Not an EP, do not draw a square Sight Error (SErr) intersection of LOP and azimuth S Err 4.0nm

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11 Celestial Fixes Celestial fix - sights on two/more different bodies taken within a short time Time interval within 20 minutes - a “Fix” Time interval longer - a “Running Fix” Offshore navigators rely on Sun RFix Morning LOP advanced to midday Midday LOP advanced to evening Evening LOP advanced to next morning

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45ºN 30’ 20’ 10’ 50’ 40’ 30’ 45ºN 30’ 20’ 10’ 50’ 40’ 30’ Advancing a LOP using a construction line that parallels the DR track 0800 Sun 1200 Sun Sun 1200 RFix C 260 S 6.0 C 200 S Plotting a Celestial R Fix 0.9nm T 245 º 0.8nm A 332 º

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45ºN 30’ 20’ 10’ 50’ 40’ 30’ 45ºN 30’ 20’ 10’ 50’ 40’ 30’ 0800 Sun 1200 Sun Sun 1200 RFix C 200 S Advancing a LOP using direction and distance between DR’s. Plotting a Celestial R Fix C 260 S nm T 245 º 0.8nm A 332 º

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45ºN 30’ 20’ 10’ 50’ 40’ 30’ 45ºN 30’ 20’ 10’ 50’ 40’ 30’ 0800 Sun 1200 Sun Sun 1200 RFix C 200 S Advancing a LOP using the original intercept and azimuth Plotting a Celestial R Fix C 260 S nm T 245 º 0.8nm A 332 º

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Sight Folder Plotting 45ºN 30’ 20’ 10’ 50’ 40’ 30’ 93ºW 30’50’ 40’ 20’ 10’ 1245 Sun 0858 Sun GPS S Err 3.6nm 1245 RFix

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Sight Folder Plotting 45ºN 30’ 20’ 10’ 50’ 40’ 30’ 93ºW 30’50’ 40’ 20’ 10’ 1245 Sun 0858 Sun 0858 GPS S Err 4.0nm Sun 1245 RFix 1245 GPS Changing position where sights taken. Resulting RFix must still be within 5.0nm of later sight.

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17 Offshore: plotting & labeling of courses & bearings – referenced to TRUE Offshore: plotting & labeling of courses & bearings – referenced to TRUE Universal plotting sheets used in any part of the ocean except Polar Regions Universal plotting sheets used in any part of the ocean except Polar Regions Likely to cross several lines of variation offshore. Likely to cross several lines of variation offshore. Using True, apply Var & Dev for each leg to determine Compass course to steer. Using True, apply Var & Dev for each leg to determine Compass course to steer. Universal Plotting Sheets

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18 The UPS covers about 4° of latitude and 4° of longitude Draw meridian through marks on Compass Rose at desired mid-latitude

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19 Universal Plotting Sheets Setup for mid-latitude of 37° N and mid-longitude of 68° W Will be used for chapter 13 homework cruise

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20 Setup for mid-latitude of 37° N and mid-longitude of 68° W Universal Plotting Sheets Set dividers to the spacing between central meridian and the one drawn Measure off and draw remaining meridians Label 68º W 69º70º66º67º 37ºN 38º 39º 36º 35º

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21 Universal Plotting Sheets 68º W 69º70º66º67º 37ºN 38º 39º 36º 35º Distance & latitude -measured along Latitude scale on central meridian Longitude - measured on pre-printed scale draw line across at value of mid-lat 35 º 36 º 37 º 38 º 39 º

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22 Longitude Measurements Measure 15’ of Longitude at 37° Latitude. Precision on UPS – 1.0nm or 1’ of Latitude/Longitude. 10’5’ +

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23 Universal Plotting Sheets 68º W 69º70º66º67º 37ºN 38º 39º 36º 35º (ZD+5) (ZD+4) Time Zone Boundaries Vertical dashed line, with ZD on both sides 15º W Var Isogonic Lines Lines of equal magnetic variation Dashed line, with variation shown Plot the 15º W isogonic line using points: L 1 39º 00’ N, Lo 1 69º 20’ W and L 2 35º 00’ N, Lo 2 66º 45’ W… 15º W Var YOU WILL USE THIS UPS FOR PLOTTING THE CHAPTER 13 HOMEWORK CRUISE

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24 Universal Plotting Sheets 68º W 69º70º66º67º 37ºN 38º 39º 36º 35º (ZD+5) (ZD+4) 15º W Var DOUBLING THE SCALE 37ºN 30’ 38º 30’ 36º 68º W 30’69º67º30’ (ZD+5) (ZD+4) 15º W Var

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25 Meridian Transit Celestial body crosses upper branch of observer’s meridian – body reaches maximum altitude LHA is 000° Body due north/south Azimuth 360º or 180º Nav. triangle collapses to straight line - elevated pole, observer, & GP of body - all on same great circle: the observer’s meridian Observer GP Sun Equator Greenwich Pn Meridian Transit of Sun also known as Local Apparent Noon (LAN)

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26 Finding Time of Transit Mean time of transit is calculated

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27 Find ZT of MT on 14 Nov at Lo 092° 21.2´W Step 1 Record the DR Lo Step 2 Find whole hour GHA from daily page of Nautical Almanac, closest to, but still smaller than DR Lo Finding Time of Transit 14

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Step 3 Record GHA Step 4 Subtract whole hour GHA from DR Lo Step 5 Browse increments / corrections pages Finding Time of Transit Find ZT of MT on 14 Nov at Lo 092° 21.2´W

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29 Step 6 Record increment Step 7 Add to GHA whole hour Step 5 Correct for ZD ZD: 21.2’ / 60 = º / 15 = 6.15 Finding Time of Transit Find ZT of MT on 14 Nov at Lo 092° 21.2´W

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30 The Ultimate Backup Determine Lat w/o calculator, tables, or plotting Simple and easy to teach to crew members Quick check of GPS latitude However, limited availability Only once a day, at a specific time Computing Latitude

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31 Correct WT and hs of the sight at maximum altitude Subtract Ho from 90° to obtain Co-Alt For UT of the sight, obtain Dec of sun from Almanac Combine Co-Alt and Dec to obtain your latitude L = Dec + Co-Alt

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32 Observer North of Sun 50 ° N 50 ° S Equator CoAlt Sun Observer Computing Latitude

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33 50 ° N 50 ° S Equator CoAlt Sun Observer Computing Latitude Observer South of Sun

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34 Taking the Noon Sight Begin taking sights 10 to 20 minutes before ZT of MT Take observations every minute or two Note altitude and time Rate of altitude increase slows as sun approaches meridian transit Near transit, altitude may appear nearly constant for a few minutes Helpful to plot run of sights Helpful to plot run of sights

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35 Latitude from MT Sight DR position on 20 April: DR position on 20 April: L 48° 54.0´ N L 48° 54.0´ N Lo 125° 26.0´ W Lo 125° 26.0´ W From a series of sights around noon, you selected the maximum observed altitude From a series of sights around noon, you selected the maximum observed altitude hs of sun (LL) is 52° 28.9´ at 12–18–26. hs of sun (LL) is 52° 28.9´ at 12–18–26. WE 2s slow. WE 2s slow. HE 10.2 feet, IC +1.2´ HE 10.2 feet, IC +1.2´ Apr Apr – Sun Co-Alt You What’s your azimuth angle?

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36 Meridian Transit of the Sun End of Junior Navigation Chapter 9 Bring your Pilot Chart next week and Begin Preparing Sight Folders

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