Intro to Navigation

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Intro to Navigation

  1. 1. CHAPTER 1INTRODUCTION TO NAVIGATION
  2. 2. Navigation enables mariners to:• Locate their position• Travel from one place to another
  3. 3. Terrestrial Sphere or GlobeA sphere on which is depicted a mapof the Earth (terrestrial globe)
  4. 4. North Pole South PoleThe north and south poles arelocated at the ends of the axis onwhich Earth rotates.
  5. 5. North Pole Meridians South PoleLines running through the poles andaround the Earth are called meridians.
  6. 6. EquatorThe great circle of the Earth that isequidistant from the North Pole andSouth Pole(Cuts every meridian in half)
  7. 7. 60° 60° 30° Northern Hemisphere 30°0° EQUATOR 0° 30° 30° Southern Hemisphere 60° 60°
  8. 8. Northern WesternHemisphere Hemisphere North Pole North Pole South Pole South Pole Southern EasternHemisphere Hemisphere
  9. 9. HemisphereHalf of a globe
  10. 10. N pole Greenwich England W E LONGITUDE EQUATOR S poleMeridians and the equator are calledgreat circles because they divide theglobe into two halves.
  11. 11. Great CircleAny circle formed by the intersectionof a plane passing through the Earth’scenter, with the Earth’s surface
  12. 12. Prime MeridianParallels EquatorThe equator is the only great circlegoing around the globe from east towest. The other lines are called parallels,since they go around the globe parallelto, and north and south of the equator.
  13. 13. Greenwich meridian (longitude 0°) N Equator (latitude 0°)One exampleof a great circle SA great circle is any circle whoseplane passes through the Earth’scenter, no matter what direction.
  14. 14. What is the significance of thegreat circle in navigation?
  15. 15. What is the significance of the great circle in navigation?The shortest distance betweentwo points on the Earth lies alongthe path of a great circle passingthrough those two points.
  16. 16. ArcAny unbroken part of thecircumference of a circle orother curved line
  17. 17. CircumferenceThe distance around a circular area
  18. 18. What is the circumference of the Equator?
  19. 19. 360° 360° Greenwich meridian N Center of (longitude 0°) The Earth Regardless of the size of the circle, the circumference Equator (latitude 0°) has 360°.One exampleof a great circle S
  20. 20. 360° 1° = 60 minutes1 minute = 60 seconds
  21. 21. Measurement along a meridianor parallel is expressed in termsof degrees, minutes, and secondsof arc (the curve of the circle).
  22. 22. Greenwich Royal Observatory 0° 0°The Greenwich meridian is numbered0, or 0°, and is called the primemeridian.
  23. 23. Prime MeridianThe meridian running throughGreenwich, England, from whichlongitude east and west is measured
  24. 24. INTERNATIONAL DATE LINE NORTH POLE PRIME MERIDIAN
  25. 25. InternationalDate Line New Date Noon Old Date Old Day 0° Prime Meridian New Day Midnight 180° International Date Line International Date Line
  26. 26. EasternHemisphere International Date Line Equator Pacific Ocean Western Hemisphere
  27. 27. Prime Meridian 0° Longitude MeridiansMeridians (longitude lines) between theprime meridian and 180th meridian arenumbered 0° to 180° east (E) or west (W).
  28. 28. LongitudeMeasurement of position east or westfrom the prime meridian
  29. 29. Greenwich Prime Meridian W E LongitudeThe distance of arc east (E) or west (W)of the prime meridian, measured alonga parallel
  30. 30. Longitude Lines
  31. 31. LatitudeMeasurement of position north orsouth of the equator
  32. 32. LatitudeThe distance of arc north (N) orsouth (S) of the equator, measuredalong a meridian
  33. 33. Latitude LongitudeEquator Prime meridian Grid system of latitude and longitude lines
  34. 34. 90° 90° EARTH’SLATITUDE LONGITUDE GRID
  35. 35. Remember! North Pole North Latitude South Latitude West East Longitude South Longitude Pole• Longitude is always measured east or west from 0° through 180°• Latitude is always measured north or south from 0° through 90°
  36. 36. New Orleans, LA 30N, 90W
  37. 37. Washington, D.C.38°5852"Nlatitude77°0112"WlongitudeExpress latitudeand longitude indegrees, minutes,and seconds.
  38. 38. Washington, D.C.38°59N latitude77°01W longitude This is spoken as thirty-eight degrees, fifty-nine minutes north, seventy-seven degrees, one minute west.
  39. 39. Washington, D.C.38°5852"Nlatitude77°0112"WlongitudeSeconds are usedonly if very exactlocations arerequired.
  40. 40. Nautical MileOne minute of arc measured alongthe equator, or any other greatcircle
  41. 41. 6,865 Nautical Miles 6,888Nautical MilesEquatorial Diameter - 6,888 Nautical MilesPolar Diameter - 6,865 Nautical Miles
  42. 42. Comparison of a Statute Mile to a Nautical MileSTATUTE MILE = 5,280 FEET OR 1760 YARDS NAUTICAL MILE = 6,076 FEET OR 2,000 YARDS0 500 1000 1500 2000 YARDS
  43. 43. Dividers Distance on a chart is measured along the meridian, using a tool called dividers.
  44. 44. Measuring Distance
  45. 45. P 30 Nautical Miles 60° Parallel 52 Nautical30° Miles 60 Nautical Miles0°Length of a Degree of Longitude at Various Latitudes
  46. 46. Remember!Distances are notmeasured onparallels of latitude,because one minuteequals one nauticalmile only along theequator.Dividers
  47. 47. 1 knot = 1 nautical mile per hour
  48. 48. Origin of the term knot Chip LogAn old sailing day’s log for measuringthe speed of a vessel
  49. 49. True Nautical DirectionMeasured from true north (North Pole)as located on a globe
  50. 50. 32-point Compass
  51. 51. Cardinal PointsThe four primary directions of thecompass; the north, south, east,and west points
  52. 52. Cardinal DirectionsNorth, South, East, West:the four primary directionsof the compass
  53. 53. On the compass rose above, only northis filled in. Fill in the rest of the pointson the compass, going clockwise, usingthe standard abbreviations.
  54. 54. On the compass rose above, only northis filled in. Fill in the rest of the pointson the compass, going clockwise, usingthe standard abbreviations.
  55. 55. Express nautical directions inthree digits:065° (Zero six five degrees)090° (Zero nine zero degrees)
  56. 56. Heading – Direction the ship is facingCourse – Direction the ship is steeredthrough the water
  57. 57. MAGNETIC COMPASS GYROCOMPASSMagnetic compasses Gyrocompassesgive direction relative reference trueto magnetic north. north.
  58. 58. GyrocompassNavigational compass containing agyroscope, that, when adjusted forlatitude and speed, shows true northor communicates this informationto one or more gyro repeaters.
  59. 59. MAGNETIC TRUE NORTH NORTH
  60. 60. Magnetic CompassA compass having a magnetizedneedle generally in line with themagnetic poles of the Earth
  61. 61. NORTH MAGNETIC POLE Canada United StatesMagnetic compasses point to theEarth’s northernmost magnetic pole,located in northern Canada.
  62. 62. Variation AngleDifference between magnetic and truenorth in degrees
  63. 63. How Variation Affects the Compass Magnetic North North Pole VariationRemember, variation changesdepending on your position relativeto magnetic north.
  64. 64. Converting DirectionTo convert from magnetic to true,just add or subtract the variationat your location to the magneticbearing.Remember — Westerly variationsare subtracted, and easterlyvariations are added.
  65. 65. Example of Converting DirectionIf your ship was heading 080° magneticin a region where the variation was10° East, what is the true heading?
  66. 66. Example of Converting DirectionIf your ship was heading 080° magneticin a region where the variation was10° East, the true heading would be080° + 10°, or 090° true.
  67. 67. Example of Converting DirectionIf your ship was heading 270° true in aregion where the variation was 10° East,what is the magnetic heading?
  68. 68. Example of Converting DirectionIf your ship was heading 270° true in aregion where the variation was 10° East,the true heading would be 270° – 10°,or 260° magnetic heading.
  69. 69. BearingThe direction of an object from anobserver, measured clockwise in oneof three standard ways:• True bearing• Magnetic bearing• Relative bearing
  70. 70. TN Light House 090° TRUE BEARINGTrue Bearing
  71. 71. True BearingBearing using true north as thereference
  72. 72. MAGNETIC TRUE NORTH NORTH Light HouseDifference between true and magnetic bearing
  73. 73. Magnetic BearingThe direction of an object measuredclockwise from magnetic north
  74. 74. TN RELATIVE BEARING 030° Light HouseRelative Bearing
  75. 75. Relative BearingThe direction of an object measuredclockwise from the ship’s head (bow)
  76. 76. When recording a bearing, assume it tobe a true bearing unless followed by theletters M or R.030°M means 30° right of magnetic north030°R means 30° off the starboard bow
  77. 77. Objects seen by lookouts are reportedin terms of relative bearing by degrees.
  78. 78. Relative Bearings• Dead ahead, or bow – 000°R• Starboard beam – 090°R• Dead astern – 180°R• Port beam – 270°R
  79. 79. To emphasize that it is a true bearing,the letter T (for example 030°T) followsthe three-digit true bearing, spoken―030 degrees true.‖
  80. 80. TN RELATIVE BEARING 030° 090° TRUE Light BEARING HouseTrue Bearing = Relative Bearing + True Heading(Subtract 360° if sum is greater than 360°)
  81. 81. Nautical ChartType of map used to navigate onwater
  82. 82. Nautical ChartA nauticalchart is astandardizeddrawingrepresentingpart of thenavigablewaters of theEarth.
  83. 83. HydrographyScience of measurement, description,and mapping of the Earth’s surfacewaters, with special reference to theiruse for navigation
  84. 84. Hydrographic informationgiven on a chart includes:• Water depths• Nature of bottom• Overhead obstructions• Navigation aids; buoys, lights, and anchorages
  85. 85. Globe ChartImpossible to Necessary towork navigation work navigationproblems or problemschart courses
  86. 86. CartographersMakers of maps and charts who usemath to work out chart projectiontechniques
  87. 87. It is necessaryto convert theround surface ofthe globe to onethat is flat andtwo-dimensional(having onlylength andwidth)—toa flat piece ofpaper on which achart is drawn.
  88. 88. Planar Conical CylindricalOrthographic Perspective Conic MercatorChart projections
  89. 89. Chart ProjectionFlat surface representative of theEarth
  90. 90. Mercator ProjectionThe best-known map or chart projection
  91. 91. Mercator ProjectionEarth is projected onto acylinder-shaped piece of paper,wrapped around the globe at theequator
  92. 92. Geradus Mercator Mercator Projection• Commonly used for navigational charts• Developed by a Dutch cartographer, Geradus Mercator, in the 1500s• Most useful projection for navigation
  93. 93. Great Circle Track Rhumb Line Conformal ProjectionA projection on which any rhumb line is shownas a straight line, used chiefly in navigation,though the scale varies with latitude and aerialsize and the shape of large areas are greatlydistorted
  94. 94. Rhumb LineA curve on the surface of a spherethat cuts all meridians at the sameangle; the path taken by a vessel oraircraft that maintains a constantcompass direction
  95. 95. Scale of Charts SCALE 1:7,500,000• Used to measure distance• Relationship between actual and chart distance• Printed near the legend as a ratio, such as 1:7,500,000
  96. 96. Small scalesare used todepict largeareas on achart, andlarge scalesare used todepict smallareas.
  97. 97. Measuring distance on a chartIf an inch on the chart represents 50 miles,what would five inches represent?
  98. 98. Measuring distance on a chartIf an inch on the chart represents 50 miles,what would five inches represent? 250 Miles
  99. 99. Remember• The larger the scale, the smaller the area shown on a given chart or map.• The large-scale charts show areas in great detail.• Features appearing on a large-scale chart may not show up at all on a small-scale chart of the same area.
  100. 100. Nautical Sailing Types of Charts Harbor
  101. 101. Nautical charts have information forsafe navigation, such as:• Symbols, figures, and abbreviations• Depth of water• Type of bottom• Navigational aids
  102. 102. Harbor charts are large-scale charts thatshow harbors and their approaches indetail.
  103. 103. Coastalcharts areintermediate-scale chartsused tonavigate avessel whoseposition maybe determinedby landmarksand lights,buoys, orsoundingsoffshore.
  104. 104. SoundingThe act of measuring the depth of anarea of water
  105. 105. Generalocean sailingcharts aresmall-scalechartsshowing theapproachesto largeareas of thecoast.
  106. 106. INTRODUCTION TO NAVIGATION End of Part 1
  107. 107. INTRODUCTION TO NAVIGATION Part 2
  108. 108. Depths ofwater maybe given infeet, fathoms,or meters.
  109. 109. Fathom (of depth)A unit of length equal to six feet(1.8 meters); used chiefly in nauticalmeasurements
  110. 110. Plotting
  111. 111. Plotting In order to use the nautical chart fornavigating, you must know something about how courses, bearings, and lines of position are plotted on it.
  112. 112. Parallel Rulers
  113. 113. Parallel RulersA pair of straightedges connected bytwo pivoted crosspieces of equallength so as to be parallel at all times;used for various navigationalpurposes, especially for transferringthe bearing of a plotted course to acompass rose
  114. 114. ProtractorAn instrument having a graduated arcfor plotting or measuring angles
  115. 115. Three-Arm Parallel MotionProtractor Protractor (PMP)
  116. 116. MeasuringDistance on aMercator Chart
  117. 117. Fix (position)Accurate position determined withoutuse of any previous position, usingvisual, electronic, or celestialobservation
  118. 118. Line of Position (LOP)A line indicatinga series of possiblepositions of a shipas a result ofobservation ormeasurement
  119. 119. SPIRE RANGE BEARING Lines of PositionCAPE DISTANCE ARC TANGENT
  120. 120. Bearing Lines of PositionLines corresponding to the bearingsare plotted on the chart. They arelabeled with the 4-digit time ofobservation above the line.
  121. 121. Visual RangeTwo landmarks or navigation aids areobserved in line, one behind the other
  122. 122. Rear Marker Front MarkerRear Marker Visual Range Front Marker
  123. 123. A circular line of position Distance Arc
  124. 124. Radar StadimeterDevices used tomeasure distanceto a landmark Sextant
  125. 125. Stadimeter Optical distance-measuring device that measures angles to determine distance to an object using as areference the distance to an object of known height
  126. 126. Stadimeter
  127. 127. SextantAn astronomical instrument used todetermine latitude and longitude atsea by measuring angular distances,especially the altitudes of Sun, Moon,and stars
  128. 128. Sextant
  129. 129. Obtain a fix with these combinationsof lines of position:• Two or more lines of bearing• A distance arc and a line of bearing• Two or more distance arcs• A visual range and a distance arc• A visual range and a line of bearing• Two simultaneous visual ranges Most commonly used
  130. 130. TOWER 1545 A fix from two crossed bearings
  131. 131. DOUBLE POINT LIGHT A fix by a bearing and distance from the same object 1314
  132. 132. SMITH POINTHALL REEF LIGHT A fix from three JONES intersecting BLUFF bearings
  133. 133. LIGHT WA fix from twovisual ranges LIGHT X LIGHT 2152 W
  134. 134. Visual FixElectronic/Celestial FixDead Reckoning PositionEstimated PositionPlotting Symbols
  135. 135. LIGHTHOUSE 1300 FIX1245 FIX TOWER FACTORY Marking Ship’s Fix
  136. 136. PilotingThe determinationof position byvisual means
  137. 137. PilotingThe determination of the course orposition of a ship or airplane by anyof various navigational methods ordevices
  138. 138. Navigation Aids Compass Bearing Circle Fathometer Chart Stadimeter Radar BuoyLighthouse
  139. 139. Echo sounder (Fathometer)Sonic device used to measure waterdepth
  140. 140. Fathometer
  141. 141. Echo Sounder
  142. 142. Sound RangingA method for determining the distancebetween a point and the position of asound source by measuring the timelapse between the origin of the soundand its arrival at the point SONAR (S0und NAvigation and Ranging)
  143. 143. In piloting, soundings are usuallytaken every 5 minutes. D=1/2 t x 4,800 feet per second
  144. 144. A fathometer mayestablish a fixwhen a navigatorhas a chartshowing accuratebottom contours,but in practice itusually serves asa check.
  145. 145. Electronic navigation isa form of piloting.
  146. 146. Electronic Navigation Advantages• Unaffected by weather• Determines ship position electronically Disadvantages • Equipment malfunction • Insufficient coverage
  147. 147. RADARRAdio Detection And Ranging
  148. 148. RADARNavigation system using reflectedpulses of energy
  149. 149. RADAR
  150. 150. Advantage of radar, as a navigationalaid, is that it does not require externaltransmitting stations.
  151. 151. Disadvantage of radar, as a navigationalaid, is that maximum range is currentlylimited to slightly more than line-of-sight.
  152. 152. LighthouseUse Reliable Radar Targets
  153. 153. Radar System
  154. 154. PIPSTargets appear on the scope asbright spots of light called pips.
  155. 155. The most common scope used is a planposition indicator (PPI), which gives abird’s eye view of the radar coveragearea, the transmitting ship in the center.
  156. 156. Advantages of radar as a navigationalaid include: • It can be used at night and during periods of low visibility. • A fix can be obtained from a single object.
  157. 157. • Very accurate and rapid• Used to locate and track storms• Very important for ship safety
  158. 158. LoranLong Range Navigation
  159. 159. LoranLong range navigation system usingradio signals
  160. 160. Loran is a systemof radio signalsbroadcast bystations of knownposition.
  161. 161. Loran ReceiverA loran fix is determined by a loranreceiver from the intersection of linesof position obtained from those shorestations.
  162. 162. GPS Satellites Satellite NavigationThe newest electronic navigation systemis the Global Positioning System (GPS).
  163. 163. Global Positioning System (GPS) • Six 10,900- mile-high orbits • 24 satellites • Continuous three- dimensional fix capability • Fix accurate to within ±10 meters
  164. 164. GPS Navigation
  165. 165. GPS is used for a wide variety of landnavigation purposes, including positionand direction-finding in many new carsand golf carts.
  166. 166. Military applications of GPS navigationsystems include guidance for: • Smart bombs • Cruise missiles
  167. 167. Differential GPSEnhancement by to basic GPS: corrections topositioning information is determined by land-based receivers and transmitted to users.Capable of accuracy to within + 1 meter.
  168. 168. Ship’s Inertial Navigation System (SINS)Provides accurate and continuousdead reckoning (DR) positions
  169. 169. SINS gives ships an accurate andcontinuous dead reckoning positionusing three gyroscopes to determinelatitude, vertical, and longitude withgreat accuracy.
  170. 170. Submarines use SINS to navigate whensubmerged for months even whentraveling under the Arctic ice cap.
  171. 171. CelestialSphere Celestial NavigationBranch of navigation in which position isdetermined by the aid of heavenly bodiessuch as the Sun, Moon, and selected starsand planets
  172. 172. The widespread availability of GPS isfast making celestial navigation at seaa vanishing art.
  173. 173. The sextant is used in celestialnavigation to measure the angle(altitude) between a heavenly bodyand the visible horizon.
  174. 174. Sextants
  175. 175. INDEX MIRROR LENSHORIZON INDEX ARM HOODMIRROR TELESCOPE VERNIER ARC SCALESCALE MICROMETER DRUM SCALE SCREW Sextant — Nomenclature Reading the Vernier Scale
  176. 176. Dead ReckoningCalculation of ones position on thebasis of distance run on variousheadings since the last preciselyobserved position, with as accurateallowance as possible being made forwind, currents, compass errors
  177. 177. Visual FixElectronic/Celestial FixDead Reckoning PositionEstimated PositionPlotting Symbols
  178. 178. FIX DR POSITION DESTINATION1200 DEAD RECKONING TRACK
  179. 179. Set and DriftSet – The direction in which a ship is forced by wind and currentDrift – The speed of that force in knots
  180. 180. FIX DR POSITION DESTINATION 1615 16001200 Effect of Set and Drift
  181. 181. A fix at 1200 is plotted and labeled.
  182. 182. A line is drawn from the fix on theship’s course of 073°. Course islabeled above the line, and thespeed of 15 knots is labeled belowthe line.
  183. 183. To find the 1300 DR position, usedividers to measure 15 minutes oflatitude on the vertical latitudescale printed on the side of thechart.
  184. 184. The spot is labeled ―1300DR.‖
  185. 185. The Captain orders the Officerof the Deck (OOD) to put ship ona new course, 117° at 1330.
  186. 186. Using dividers, mark a spot 7½miles from the 1300 DR positionalong the direction the ship issteaming.
  187. 187. Label position 1330DR, anddraw a new course line in thedirection of 117°.
  188. 188. Plotting a ship’s DR track from one fix to the next is a1400 FIX continuous process while underway.
  189. 189. DR PLOT1400 FIX
  190. 190. At sea, the navigator will use celestial orelectronic means to get positive fixes atleast every morning, noon, and evening.
  191. 191. In piloting waters, the navigator willnormally be on the bridge getting exactfixes whenever usable navigation aidscome into sight.
  192. 192. Currently, electronic plotters incorporatecontinuous fix updates received fromGPS, then project current ship’s positionand the DR track onto an electronic chartprojection on a computer screen.
  193. 193. Q.1. Define navigation.
  194. 194. Q.1. Define navigation.A.1. The art and science by which mariners find their ships position and guide it safely from one point to another
  195. 195. Q.2. What is a chart?
  196. 196. Q.2. What is a chart?A.2. A type of map used to navigate on water
  197. 197. Q.3. What are the imaginary lines that run through the poles and around the Earth?
  198. 198. Q.3. What are the imaginary lines that run through the poles and around the Earth?A.3. Meridians or lines of longitude
  199. 199. Q.4. What divides the Earth into the northern and southern hemispheres?
  200. 200. Q.4. What divides the Earth into the northern and southern hemispheres?A.4. The Equator
  201. 201. Q.5. What is a Great Circle?
  202. 202. Q.5. What is a Great Circle?A.5. Any circle drawn around the Earth, the plane of which divides the Earth into two equal parts
  203. 203. Q.6. Are all meridians great circles?
  204. 204. Q.6. Are all meridians great circles?A.6. Yes
  205. 205. Q.7. What is the name given to the meridian on which the Royal Observatory at Greenwich, England, is located?
  206. 206. Q.7. What is the name given to the meridian on which the Royal Observatory at Greenwich, England, is located?A.7. The Prime Meridian
  207. 207. Q.8. Do parallel and latitudinal lines run in the same direction?
  208. 208. Q.8. Do parallel and latitudinal lines run in the same direction?A.8. Yes
  209. 209. Q.9. Navigators determine their ships position using what coordinate system?
  210. 210. Q.9. Navigators determine their ships position using what coordinate system?A.9. Latitude and Longitude
  211. 211. Q.10. If the latitude of the equator is 0 degrees, what is the latitude of the North Pole?
  212. 212. Q.10. If the latitude of the equator is 0 degrees, what is the latitude of the North Pole?A.10. 90 degrees or north
  213. 213. Q.11. Latitude and longitude are expressed in what units?
  214. 214. Q.11. Latitude and longitude are expressed in what units?A.11. Degrees, minutes, and seconds
  215. 215. Q.12. How many degrees are there in a circle?
  216. 216. Q.12. How many degrees are there in a circle?A.12. 360
  217. 217. Q.13. Approximately how many yards are in a nautical mile?
  218. 218. Q.13. Approximately how many yards are in a nautical mile?A.13. 2000 yds.
  219. 219. Q.14. What are meridians?
  220. 220. Q.14. What are meridians?A.14. Great Circles which pass through the Earth’s poles
  221. 221. Q.15. In navigation what is a ―knot?‖
  222. 222. Q.15. In navigation what is a ―knot?‖A.15. A seagoing term meaning one nautical mile per hour
  223. 223. Q.16. How is direction expressed?
  224. 224. Q.16. How is direction expressed?A.16. As an angle between 000 degrees and 359 degrees
  225. 225. Q.17. What are the cardinal points?
  226. 226. Q.17. What are the cardinal points?A.17. North, East, South, and West
  227. 227. Q.18. Define ―true bearing.‖
  228. 228. Q.18. Define ―true bearing.‖A.18. The direction of an object measured clockwise from true north
  229. 229. Q.19. What does chart projection entail?
  230. 230. Q.19. What does chart projection entail?A.19. Projecting a three-dimensional object on a two-dimensional plane
  231. 231. Q.20. What is the best-known map or chart projection called?
  232. 232. Q.20. What is the best-known map or chart projection called?A.20. Mercator projection
  233. 233. Q.21. What are the three basic types of charts used by the Navy?
  234. 234. Q.21. What are the three basic types of charts used by the Navy?A.21. a. Navigational b. Harbor c. General ocean sailing charts
  235. 235. Q.22. What is a cartographer?
  236. 236. Q.22. What is a cartographer?A.22. One who makes maps and charts
  237. 237. Q.23. What is a fix?
  238. 238. Q.23. What is a fix?A.23. An accurate position determined without reference to any previous position. The intersection of 2 or more lines of position.
  239. 239. Q.24. What is the difference between directions measured on a gyrocompass and those measured on a magnetic compass?
  240. 240. Q.24. What is the difference between directions measured on a gyrocompass and those measured on a magnetic compass?A.24. Directions measured on a gyrocompass are relative to true north, whereas directions measured on a magnetic compass are relative to magnetic north.
  241. 241. Q.25. How is distance on a Mercator chart measured?
  242. 242. Q.25. How is distance on a Mercator chart measured?A.25. On a flat surface along any meridian where one minute of latitude equals one nautical mile
  243. 243. Q.26. If a half-inch on a chart represents 10 miles, how many inches would represent 100 miles?
  244. 244. Q.26. If a half-inch on a chart represents 10 miles, how many inches would represent 100 miles?A.26. Five inches
  245. 245. Q.27. What is the shortest distance between two points on a globe?
  246. 246. Q.27. What is the shortest distance between two points on a globe?A.27. An arc of a great circle
  247. 247. Q.28. How many feet are in one fathom?
  248. 248. Q.28. How many feet are in one fathom?A.28. Six feet
  249. 249. Q.29. What is a line of position (LOP)?
  250. 250. Q.29. What is a line of position (LOP)?A.29. A line drawn on a chart along which a ship must be located, based on a bearing or distance from an object or landmark
  251. 251. Q.30. A ship that is traveling south observes another ship on a relative bearing of 041 degrees. What is the true bearing to that ship?
  252. 252. Q.30. A ship that is traveling south observes another ship on a relative bearing of 041 degrees. What is the true bearing to that ship?A.30. 221 degrees true (180 degrees + 041 degrees)
  253. 253. Q.31. A ship that is traveling north observes another ship on a relative bearing of 041 degrees. Where would you see that ship in relation to your ship?
  254. 254. Q.31. A ship that is traveling north observes another ship on a relative bearing of 041 degrees. Where would you see that ship in relation to your ship?A.31. Off the starboard bow
  255. 255. SphereA round body whose surface is at allpoints equidistant from the center
  256. 256. MeridianA great circle of the Earth passingthrough the poles and any givenpoint on the Earths surface
  257. 257. ParallelLines of latitude with only the equatorbeing a great circle
  258. 258. DividersA two–pointed compass used fordividing lines and measuring
  259. 259. Compass CardA circular card with magnets attachedto its underside, the face divided on itsrim into points of the compass, degreesclockwise from north, or both, andfloating or suspended from a pivot soas to rotate freely
  260. 260. Magnetic CompassDirectional instrument that points tothe north magnetic pole GyrocompassAligned with true north by means of aspinning gyroscope
  261. 261. DistortionThe state of being misrepresenteda false
  262. 262. Developmentof a MercatorProjection
  263. 263. Sounding
  264. 264. LORAN CHART
  265. 265. Global Positioning System (GPS) Electronic navigation system using satellites

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