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Intro to Navigation

  1. 1. CHAPTER 1 INTRODUCTION TO NAVIGATION
  2. 2. Navigation enables mariners to: • Locate their position • Travel from one place to another
  3. 3. Terrestrial Sphere or Globe A sphere on which is depicted a map of the Earth (terrestrial globe)
  4. 4. North Pole South Pole The north and south poles are located at the ends of the axis on which Earth rotates.
  5. 5. North Pole Meridians South Pole Lines running through the poles and around the Earth are called meridians.
  6. 6. Equator The great circle of the Earth that is equidistant from the North Pole and South 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 Western Hemisphere Hemisphere North Pole North Pole South Pole South Pole Southern Eastern Hemisphere Hemisphere
  9. 9. Hemisphere Half of a globe
  10. 10. N pole Greenwich England W E LONGITUDE EQUATOR S pole Meridians and the equator are called great circles because they divide the globe into two halves.
  11. 11. Great Circle Any circle formed by the intersection of a plane passing through the Earth’s center, with the Earth’s surface
  12. 12. Prime Meridian Parallels Equator The equator is the only great circle going around the globe from east to west. The other lines are called parallels, since they go around the globe parallel to, and north and south of the equator.
  13. 13. Greenwich meridian (longitude 0°) N Equator (latitude 0°) One example of a great circle S A great circle is any circle whose plane passes through the Earth’s center, no matter what direction.
  14. 14. What is the significance of the great circle in navigation?
  15. 15. What is the significance of the great circle in navigation? The shortest distance between two points on the Earth lies along the path of a great circle passing through those two points.
  16. 16. Arc Any unbroken part of the circumference of a circle or other curved line
  17. 17. Circumference The 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 example of a great circle S
  20. 20. 360° 1° = 60 minutes 1 minute = 60 seconds
  21. 21. Measurement along a meridian or parallel is expressed in terms of degrees, minutes, and seconds of arc (the curve of the circle).
  22. 22. Greenwich Royal Observatory 0° 0° The Greenwich meridian is numbered 0, or 0°, and is called the prime meridian.
  23. 23. Prime Meridian The meridian running through Greenwich, England, from which longitude east and west is measured
  24. 24. INTERNATIONAL DATE LINE NORTH POLE PRIME MERIDIAN
  25. 25. International Date Line New Date Noon Old Date Old Day 0° Prime Meridian New Day Midnight 180° International Date Line International Date Line
  26. 26. Eastern Hemisphere International Date Line Equator Pacific Ocean Western Hemisphere
  27. 27. Prime Meridian 0° Longitude Meridians Meridians (longitude lines) between the prime meridian and 180th meridian are numbered 0° to 180° east (E) or west (W).
  28. 28. Longitude Measurement of position east or west from the prime meridian
  29. 29. Greenwich Prime Meridian W E Longitude The distance of arc east (E) or west (W) of the prime meridian, measured along a parallel
  30. 30. Longitude Lines
  31. 31. Latitude Measurement of position north or south of the equator
  32. 32. Latitude The distance of arc north (N) or south (S) of the equator, measured along a meridian
  33. 33. Latitude Longitude Equator Prime meridian Grid system of latitude and longitude lines
  34. 34. 90° 90° EARTH’S LATITUDE 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°58'52"N latitude 77°01'12"W longitude Express latitude and longitude in degrees, minutes, and seconds.
  38. 38. Washington, D.C. 38°59'N latitude 77°01'W longitude This is spoken as thirty-eight degrees, fifty-nine minutes north, seventy-seven degrees, one minute west.
  39. 39. Washington, D.C. 38°58'52"N latitude 77°01'12"W longitude Seconds are used only if very exact locations are required.
  40. 40. Nautical Mile One minute of arc measured along the equator, or any other great circle
  41. 41. 6,865 Nautical Miles 6,888 Nautical Miles Equatorial Diameter - 6,888 Nautical Miles Polar Diameter - 6,865 Nautical Miles
  42. 42. Comparison of a Statute Mile to a Nautical Mile STATUTE MILE = 5,280 FEET OR 1760 YARDS NAUTICAL MILE = 6,076 FEET OR 2,000 YARDS 0 500 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 Nautical 30° Miles 60 Nautical Miles 0° Length of a Degree of Longitude at Various Latitudes
  46. 46. Remember! Distances are not measured on parallels of latitude, because one minute equals one nautical mile only along the equator. Dividers
  47. 47. 1 knot = 1 nautical mile per hour
  48. 48. Origin of the term knot Chip Log An old sailing day’s log for measuring the speed of a vessel
  49. 49. True Nautical Direction Measured from true north (North Pole) as located on a globe
  50. 50. 32-point Compass
  51. 51. Cardinal Points The four primary directions of the compass; the north, south, east, and west points
  52. 52. Cardinal Directions North, South, East, West: the four primary directions of the compass
  53. 53. On the compass rose above, only north is filled in. Fill in the rest of the points on the compass, going clockwise, using the standard abbreviations.
  54. 54. On the compass rose above, only north is filled in. Fill in the rest of the points on the compass, going clockwise, using the standard abbreviations.
  55. 55. Express nautical directions in three digits: 065° (Zero six five degrees) 090° (Zero nine zero degrees)
  56. 56. Heading – Direction the ship is facing Course – Direction the ship is steered through the water
  57. 57. MAGNETIC COMPASS GYROCOMPASS Magnetic compasses Gyrocompasses give direction relative reference true to magnetic north. north.
  58. 58. Gyrocompass Navigational compass containing a gyroscope, that, when adjusted for latitude and speed, shows true north or communicates this information to one or more gyro repeaters.
  59. 59. MAGNETIC TRUE NORTH NORTH
  60. 60. Magnetic Compass A compass having a magnetized needle generally in line with the magnetic poles of the Earth
  61. 61. NORTH MAGNETIC POLE Canada United States Magnetic compasses point to the Earth’s northernmost magnetic pole, located in northern Canada.
  62. 62. Variation Angle Difference between magnetic and true north in degrees
  63. 63. How Variation Affects the Compass Magnetic North North Pole Variation Remember, variation changes depending on your position relative to magnetic north.
  64. 64. Converting Direction To convert from magnetic to true, just add or subtract the variation at your location to the magnetic bearing. Remember — Westerly variations are subtracted, and easterly variations are added.
  65. 65. Example of Converting Direction If your ship was heading 080° magnetic in a region where the variation was 10° East, what is the true heading?
  66. 66. Example of Converting Direction If your ship was heading 080° magnetic in a region where the variation was 10° East, the true heading would be 080° + 10°, or 090° true.
  67. 67. Example of Converting Direction If your ship was heading 270° true in a region where the variation was 10° East, what is the magnetic heading?
  68. 68. Example of Converting Direction If your ship was heading 270° true in a region where the variation was 10° East, the true heading would be 270° – 10°, or 260° magnetic heading.
  69. 69. Bearing The direction of an object from an observer, measured clockwise in one of three standard ways: • True bearing • Magnetic bearing • Relative bearing
  70. 70. TN Light House 090° TRUE BEARING True Bearing
  71. 71. True Bearing Bearing using true north as the reference
  72. 72. MAGNETIC TRUE NORTH NORTH Light House Difference between true and magnetic bearing
  73. 73. Magnetic Bearing The direction of an object measured clockwise from magnetic north
  74. 74. TN RELATIVE BEARING 030° Light House Relative Bearing
  75. 75. Relative Bearing The direction of an object measured clockwise from the ship’s head (bow)
  76. 76. When recording a bearing, assume it to be a true bearing unless followed by the letters M or R. 030°M means 30° right of magnetic north 030°R means 30° off the starboard bow
  77. 77. Objects seen by lookouts are reported in 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) follows the three-digit true bearing, spoken ―030 degrees true.‖
  80. 80. TN RELATIVE BEARING 030° 090° TRUE Light BEARING House True Bearing = Relative Bearing + True Heading (Subtract 360° if sum is greater than 360°)
  81. 81. Nautical Chart Type of map used to navigate on water
  82. 82. Nautical Chart A nautical chart is a standardized drawing representing part of the navigable waters of the Earth.
  83. 83. Hydrography Science of measurement, description, and mapping of the Earth’s surface waters, with special reference to their use for navigation
  84. 84. Hydrographic information given on a chart includes: • Water depths • Nature of bottom • Overhead obstructions • Navigation aids; buoys, lights, and anchorages
  85. 85. Globe Chart Impossible to Necessary to work navigation work navigation problems or problems chart courses
  86. 86. Cartographers Makers of maps and charts who use math to work out chart projection techniques
  87. 87. It is necessary to convert the round surface of the globe to one that is flat and two-dimensional (having only length and width)—to a flat piece of paper on which a chart is drawn.
  88. 88. Planar Conical Cylindrical Orthographic Perspective Conic Mercator Chart projections
  89. 89. Chart Projection Flat surface representative of the Earth
  90. 90. Mercator Projection The best-known map or chart projection
  91. 91. Mercator Projection Earth is projected onto a cylinder-shaped piece of paper, wrapped around the globe at the equator
  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 Projection A projection on which any rhumb line is shown as a straight line, used chiefly in navigation, though the scale varies with latitude and aerial size and the shape of large areas are greatly distorted
  94. 94. Rhumb Line A curve on the surface of a sphere that cuts all meridians at the same angle; the path taken by a vessel or aircraft that maintains a constant compass 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 scales are used to depict large areas on a chart, and large scales are used to depict small areas.
  97. 97. Measuring distance on a chart If an inch on the chart represents 50 miles, what would five inches represent?
  98. 98. Measuring distance on a chart If 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 for safe navigation, such as: • Symbols, figures, and abbreviations • Depth of water • Type of bottom • Navigational aids
  102. 102. Harbor charts are large-scale charts that show harbors and their approaches in detail.
  103. 103. Coastal charts are intermediate- scale charts used to navigate a vessel whose position may be determined by landmarks and lights, buoys, or soundings offshore.
  104. 104. Sounding The act of measuring the depth of an area of water
  105. 105. General ocean sailing charts are small-scale charts showing the approaches to large areas of the coast.
  106. 106. INTRODUCTION TO NAVIGATION End of Part 1
  107. 107. INTRODUCTION TO NAVIGATION Part 2
  108. 108. Depths of water may be given in feet, fathoms, or meters.
  109. 109. Fathom (of depth) A unit of length equal to six feet (1.8 meters); used chiefly in nautical measurements
  110. 110. Plotting
  111. 111. Plotting In order to use the nautical chart for navigating, you must know something about how courses, bearings, and lines of position are plotted on it.
  112. 112. Parallel Rulers
  113. 113. Parallel Rulers A pair of straightedges connected by two pivoted crosspieces of equal length so as to be parallel at all times; used for various navigational purposes, especially for transferring the bearing of a plotted course to a compass rose
  114. 114. Protractor An instrument having a graduated arc for plotting or measuring angles
  115. 115. Three-Arm Parallel Motion Protractor Protractor (PMP)
  116. 116. Measuring Distance on a Mercator Chart
  117. 117. Fix (position) Accurate position determined without use of any previous position, using visual, electronic, or celestial observation
  118. 118. Line of Position (LOP) A line indicating a series of possible positions of a ship as a result of observation or measurement
  119. 119. SPIRE RANGE BEARING Lines of Position CAPE DISTANCE ARC TANGENT
  120. 120. Bearing Lines of Position Lines corresponding to the bearings are plotted on the chart. They are labeled with the 4-digit time of observation above the line.
  121. 121. Visual Range Two landmarks or navigation aids are observed in line, one behind the other
  122. 122. Rear Marker Front Marker Rear Marker Visual Range Front Marker
  123. 123. A circular line of position Distance Arc
  124. 124. Radar Stadimeter Devices used to measure distance to a landmark Sextant
  125. 125. Stadimeter Optical distance-measuring device that measures angles to determine distance to an object using as a reference the distance to an object of known height
  126. 126. Stadimeter
  127. 127. Sextant An astronomical instrument used to determine latitude and longitude at sea by measuring angular distances, especially the altitudes of Sun, Moon, and stars
  128. 128. Sextant
  129. 129. Obtain a fix with these combinations of 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 POINT HALL REEF LIGHT A fix from three JONES intersecting BLUFF bearings
  133. 133. LIGHT W A fix from two visual ranges LIGHT X LIGHT 2152 W
  134. 134. Visual Fix Electronic/Celestial Fix Dead Reckoning Position Estimated Position Plotting Symbols
  135. 135. LIGHTHOUSE 1300 FIX 1245 FIX TOWER FACTORY Marking Ship’s Fix
  136. 136. Piloting The determination of position by visual means
  137. 137. Piloting The determination of the course or position of a ship or airplane by any of various navigational methods or devices
  138. 138. Navigation Aids Compass Bearing Circle Fathometer Chart Stadimeter Radar Buoy Lighthouse
  139. 139. Echo sounder (Fathometer) Sonic device used to measure water depth
  140. 140. Fathometer
  141. 141. Echo Sounder
  142. 142. Sound Ranging A method for determining the distance between a point and the position of a sound source by measuring the time lapse between the origin of the sound and its arrival at the point SONAR (S0und NAvigation and Ranging)
  143. 143. In piloting, soundings are usually taken every 5 minutes. D=1/2 t x 4,800 feet per second
  144. 144. A fathometer may establish a fix when a navigator has a chart showing accurate bottom contours, but in practice it usually serves as a check.
  145. 145. Electronic navigation is a form of piloting.
  146. 146. Electronic Navigation Advantages • Unaffected by weather • Determines ship position electronically Disadvantages • Equipment malfunction • Insufficient coverage
  147. 147. RADAR RAdio Detection And Ranging
  148. 148. RADAR Navigation system using reflected pulses of energy
  149. 149. RADAR
  150. 150. Advantage of radar, as a navigational aid, is that it does not require external transmitting stations.
  151. 151. Disadvantage of radar, as a navigational aid, is that maximum range is currently limited to slightly more than line-of-sight.
  152. 152. Lighthouse Use Reliable Radar Targets
  153. 153. Radar System
  154. 154. PIPS Targets appear on the scope as bright spots of light called pips.
  155. 155. The most common scope used is a plan position indicator (PPI), which gives a bird’s eye view of the radar coverage area, the transmitting ship in the center.
  156. 156. Advantages of radar as a navigational aid 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. Loran Long Range Navigation
  159. 159. Loran Long range navigation system using radio signals
  160. 160. Loran is a system of radio signals broadcast by stations of known position.
  161. 161. Loran Receiver A loran fix is determined by a loran receiver from the intersection of lines of position obtained from those shore stations.
  162. 162. GPS Satellites Satellite Navigation The newest electronic navigation system is 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 land navigation purposes, including position and direction-finding in many new cars and golf carts.
  166. 166. Military applications of GPS navigation systems include guidance for: • Smart bombs • Cruise missiles
  167. 167. Differential GPS Enhancement by to basic GPS: corrections to positioning 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 continuous dead reckoning (DR) positions
  169. 169. SINS gives ships an accurate and continuous dead reckoning position using three gyroscopes to determine latitude, vertical, and longitude with great accuracy.
  170. 170. Submarines use SINS to navigate when submerged for months even when traveling under the Arctic ice cap.
  171. 171. Celestial Sphere Celestial Navigation Branch of navigation in which position is determined by the aid of heavenly bodies such as the Sun, Moon, and selected stars and planets
  172. 172. The widespread availability of GPS is fast making celestial navigation at sea a vanishing art.
  173. 173. The sextant is used in celestial navigation to measure the angle (altitude) between a heavenly body and the visible horizon.
  174. 174. Sextants
  175. 175. INDEX MIRROR LENS HORIZON INDEX ARM HOOD MIRROR TELESCOPE VERNIER ARC SCALE SCALE MICROMETER DRUM SCALE SCREW Sextant — Nomenclature Reading the Vernier Scale
  176. 176. Dead Reckoning Calculation of one's position on the basis of distance run on various headings since the last precisely observed position, with as accurate allowance as possible being made for wind, currents, compass errors
  177. 177. Visual Fix Electronic/Celestial Fix Dead Reckoning Position Estimated Position Plotting Symbols
  178. 178. FIX DR POSITION DESTINATION 1200 DEAD RECKONING TRACK
  179. 179. Set and Drift Set – The direction in which a ship is forced by wind and current Drift – The speed of that force in knots
  180. 180. FIX DR POSITION DESTINATION 1615 1600 1200 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 the ship’s course of 073°. Course is labeled above the line, and the speed of 15 knots is labeled below the line.
  183. 183. To find the 1300 DR position, use dividers to measure 15 minutes of latitude on the vertical latitude scale printed on the side of the chart.
  184. 184. The spot is labeled ―1300DR.‖
  185. 185. The Captain orders the Officer of the Deck (OOD) to put ship on a new course, 117° at 1330.
  186. 186. Using dividers, mark a spot 7½ miles from the 1300 DR position along the direction the ship is steaming.
  187. 187. Label position 1330DR, and draw a new course line in the direction of 117°.
  188. 188. Plotting a ship’s DR track from one fix to the next is a 1400 FIX continuous process while underway.
  189. 189. DR PLOT 1400 FIX
  190. 190. At sea, the navigator will use celestial or electronic means to get positive fixes at least every morning, noon, and evening.
  191. 191. In piloting waters, the navigator will normally be on the bridge getting exact fixes whenever usable navigation aids come into sight.
  192. 192. Currently, electronic plotters incorporate continuous fix updates received from GPS, then project current ship’s position and the DR track onto an electronic chart projection 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 ship's 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 ship's position using what coordinate system?
  210. 210. Q.9. Navigators determine their ship's 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. Sphere A round body whose surface is at all points equidistant from the center
  256. 256. Meridian A great circle of the Earth passing through the poles and any given point on the Earth's surface
  257. 257. Parallel Lines of latitude with only the equator being a great circle
  258. 258. Dividers A two–pointed compass used for dividing lines and measuring
  259. 259. Compass Card A circular card with magnets attached to its underside, the face divided on its rim into points of the compass, degrees clockwise from north, or both, and floating or suspended from a pivot so as to rotate freely
  260. 260. Magnetic Compass Directional instrument that points to the north magnetic pole Gyrocompass Aligned with true north by means of a spinning gyroscope
  261. 261. Distortion The state of being misrepresented a false
  262. 262. Development of a Mercator Projection
  263. 263. Sounding
  264. 264. LORAN CHART
  265. 265. Global Positioning System (GPS) Electronic navigation system using satellites

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