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• Shape and Size of the Earth - “a not-so-perfect sphere”
The Earth is an oblate spheroid (a close approximation to a sphere), but for navigational purposes, it is considered a “true” sphere with a circumference of 21,600 nm.
Equatorial diameter = 6,888 nm
Polar diameter = 6,865 nm (or 23 nm less)
If the earth were represented by a 12 in globe it would be depressed .04 inches or .10 centimeters.
Terrestrial Coordinate System
In order to make measurements on the sphere’s surface, we must develop a system of reference points.
When rotation is introduced, two reference points are defined- the points at which the spin axis pierces the surface of the sphere. On the Earth, these points are called the north and south poles.
• Great circle - A circle formed from the intersection of a plane passing through the center of the earth and thus dividing the earth into two equal parts.
This is the largest circle that can be drawn on the surface of the earth.
The shortest distance between two points on the earth is the arc of the great circle passing through them.
Equator - The great circle formed by a plane passing perpendicular to the polar axis. The equator divides the earth into northern and southern hemispheres and is of major importance because it is one of the two great circles from which all locations on the earth’s surface are referenced. N/S Hemisphere
Meridians (of longitude) - Any great circle formed by passing a plane through the center of the earth at right angles to the equator.
Prime Meridian - The second of two great circles that constitutes a reference line for the terrestrial coordinate system. This meridian passes through the original position of the Royal Greenwich Observatory near London, England. E/W Hemisphere
• Great circle - A circle formed from the intersection of a plane passing through the center of the earth and thus dividing the earth into two equal parts.
This is the largest circle that can be drawn on the surface of the earth.
The shortest distance between two points on the earth is the arc of the great circle passing through them.
Equator - The great circle formed by a plane passing perpendicular to the polar axis. The equator divides the earth into northern and southern hemispheres and is of major importance because it is one of the two great circles from which all locations on the earth’s surface are referenced. N/S Hemisphere
Meridians (of longitude) - Any great circle formed by passing a plane through the center of the earth at right angles to the equator.
Prime Meridian - The second of two great circles that constitutes a reference line for the terrestrial coordinate system. This meridian passes through the original position of the Royal Greenwich Observatory near London, England. E/W Hemisphere
• Great circle - A circle formed from the intersection of a plane passing through the center of the earth and thus dividing the earth into two equal parts.
This is the largest circle that can be drawn on the surface of the earth.
The shortest distance between two points on the earth is the arc of the great circle passing through them.
Equator - The great circle formed by a plane passing perpendicular to the polar axis. The equator divides the earth into northern and southern hemispheres and is of major importance because it is one of the two great circles from which all locations on the earth’s surface are referenced. N/S Hemisphere
Meridians (of longitude) - Any great circle formed by passing a plane through the center of the earth at right angles to the equator.
Prime Meridian - The second of two great circles that constitutes a reference line for the terrestrial coordinate system. This meridian passes through the original position of the Royal Greenwich Observatory near London, England. E/W Hemisphere
• Great circle - A circle formed from the intersection of a plane passing through the center of the earth and thus dividing the earth into two equal parts.
This is the largest circle that can be drawn on the surface of the earth.
The shortest distance between two points on the earth is the arc of the great circle passing through them.
Equator - The great circle formed by a plane passing perpendicular to the polar axis. The equator divides the earth into northern and southern hemispheres and is of major importance because it is one of the two great circles from which all locations on the earth’s surface are referenced. N/S Hemisphere
Meridians (of longitude) - Any great circle formed by passing a plane through the center of the earth at right angles to the equator.
Prime Meridian - The second of two great circles that constitutes a reference line for the terrestrial coordinate system. This meridian passes through the original position of the Royal Greenwich Observatory near London, England. E/W Hemisphere
• Small circle - A circle formed from the intersection of a plane not passing through the center of the earth.
Parallels (of latitude) - Any small circle on the earth’s surface that is perpendicular to the earth’s axis, parallel to the plane of the equator.
The equator is the only line of latitude that is not a small circle.
• Small circle - A circle formed from the intersection of a plane not passing through the center of the earth.
Parallels (of latitude) - Any small circle on the earth’s surface that is perpendicular to the earth’s axis, parallel to the plane of the equator.
The equator is the only line of latitude that is not a small circle.
• If a point lies between 0 and 90 degrees north of the equator, it is described as having northern latitude.
If a point lies between 0 and 90 degrees south of the equator, it is described as having southern longitude.
Latitude is abbreviated by the symbol “L” or 
• If a point lies between 0 and 90 degrees north of the equator, it is described as having northern latitude.
If a point lies between 0 and 90 degrees south of the equator, it is described as having southern longitude.
Latitude is abbreviated by the symbol “L” or 
• Meridian - Any great circle formed by passing a plane through the center of the earth at right angles to the equator
• Meridian - Any great circle formed by passing a plane through the center of the earth at right angles to the equator
• If a point lies between 000 and 180 degrees west of the Greenwich meridian, it is described as having western longitude.
Longitude is abbreviated by the Greek letter lambda () or LO.
• If a point lies between 000 and 180 degrees west of the Greenwich meridian, it is described as having western longitude.
Longitude is abbreviated by the Greek letter lambda () or LO.
• As we’ve already discussed, the earth is considered a spheroid or “not-so-perfect” sphere. Which presents a problem: How to represent the round earth on a flat piece of paper.
Just as a rubber ball, it is physically impossible to spread it out flat without some stretching or tearing.
A sphere is “non-developable” - no part of it can be spread flat without significant distortion.
We get around this by projecting the surface features of the terrestrial sphere onto other surfaces that are developable (e.g. cone and cylinder).
• CYLINDRICAL
Imagine a light bulb in the center of a globe, with a sheet of paper wrapped around it in the form of a cylinder. Meridians and parallels would be &amp;quot;projected&amp;apos;&amp;apos; onto the cylinder as straight, parallel lines..
The amount of lateral distortion steadily increases with distance from the equator. Consequently, the latitude scale must be expanded to maintain conformality (true shape). The latitude scale is expanded mathematically on all mercator charts.
The mercator projection is the most widely used projection in marine navigation
Position, distance, and direction can all be easily determined
True shape of features is maintained for small areas (it is conformal) .
Distortion of true size of surface features increases with distance from the equator (significance: always measure distance at the nearest lat).
Great circles appear as curved lines.
• Latitude is measured along a meridian and one degree of latitude is essentially the same everywhere on the earth.
1 deg Lat = 60 nm
1 min Lat = 1 nm
1 nm = 2000 yds (actually 6,076 feet)
Longitude is measured along parallels of latitude. One degree of longitude will not equal 60 nm except when measured along equator.
@ 0 Lat --- 1 = 60 nm
@ 30Lat --- 1 = 52 nm
@ 60 Lat --- 1 = 30 nm
Speed =
1 knot = 1 nm/hr (1 nm = 1.15 statutory miles)
• Navigation Section 9 Lesson 2 99-07-16
Name: Lights
• ### Intro to basic navigation lrg

1. 1. Grunt Productions 2007 INTRODUCTION TO BASIC NAVIGATION A Brief By Lance GrindleyA Brief By Lance Grindley
3. 3. Grunt Productions 2007 Table of ContentsTable of Contents  Section 6Section 6 Position Lines and FixesPosition Lines and Fixes  Section 7Section 7 TidesTides  Section 8 CurrentsSection 8 Currents  Section 9 WeatherSection 9 Weather
5. 5. Grunt Productions 2007 Navigation DefinedNavigation Defined Navigation The process of safely and efficiently directing the movements of a vessel from one place to another.
7. 7. Grunt Productions 2007 Types of NavigationTypes of Navigation 1. Piloting (Coastal) Navigation This is the process by which the ship’s position is found usually at a set interval, by taking 3 compass bearings of fixed, prominent and identifiable charted objects. These bearings, when corrected for deviation and variation are plotted on the chart, and the vessel’s position at that time is found. A sextant can be used on coastal navigation as well.
9. 9. Grunt Productions 2007 Types of NavigationTypes of Navigation 2. Dead Reckoning This type of navigation is used, working from a last known position fix. The vessel’s steady course and speed over a known period of time is used to calculate the True Course and Distance traveled over that period of time. This True Course and Distance is plotted from the last known position fix, and a Dead Reckoning Position obtained.
11. 11. Grunt Productions 2007 Types of NavigationTypes of Navigation 3. Celestial Navigation This form of navigation is using a sextant to measure the vertical angle of sun, moon, planets or stars above the horizon, combined with exact GMT time taken from a chronometer. A calculation based on a dead reckoning position, will yield the distance towards or away the celestial object from that position, and a single position line is found.
12. 12. Grunt Productions 2007 Types of NavigationTypes of Navigation 3. Celestial Navigation (Continued) If a number of stars altitudes are taken at around the same time, normally at twilight, a fix can be made. Similarly if a planet and the sun are about 60 degrees or more in azimuth, can be measured at about the same time an reasonably accurate fix can be obtained.
13. 13. Grunt Productions 2007 Types of NavigationTypes of Navigation 3. Celestial Navigation (Continued) Otherwise the most common method is to use a running fix with two sights of the sun taken over about three hours, of which one may be when the sun is due north or south.
16. 16. Grunt Productions 2007 Types of NavigationTypes of Navigation 5. Electronic Navigation (Continued) It is important that the navigator understands the limitations and error that these systems are prone to. Only then can a true appreciation of the fix accuracy be made, and the accuracy of the position of the vessel be made.
17. 17. Grunt Productions 2007 Section 2 Terrestrial CoordinateSection 2 Terrestrial Coordinate SystemSystem
18. 18. Grunt Productions 2007 For navigational purposes, it’s considered a “true” sphere with a circumference of 21,600 NM Earth: A “not-so-perfect” SphereEarth: A “not-so-perfect” Sphere
19. 19. Grunt Productions 2007 Terrestrial Coordinate SystemTerrestrial Coordinate System  Great CircleGreat Circle: The intersection of a plane passing: The intersection of a plane passing through two points on the surface of the earth andthrough two points on the surface of the earth and the center of the earth.the center of the earth.
20. 20. Grunt Productions 2007 Terrestrial Coordinate SystemTerrestrial Coordinate System  Examples are: The Equator, Meridians ofExamples are: The Equator, Meridians of Longitude, the Prime Meridian being throughLongitude, the Prime Meridian being through Greenwich, near London, United Kingdom.Greenwich, near London, United Kingdom.
21. 21. Grunt Productions 2007 EquatorEquator  The great circle formed by passing a planeThe great circle formed by passing a plane perpendicular to the earth’s axis halfway betweenperpendicular to the earth’s axis halfway between its poles.its poles.
22. 22. Grunt Productions 2007 EquatorEquator  The equator divides the earth into northern andThe equator divides the earth into northern and southern hemispheres.southern hemispheres.  One of the two great circles from which allOne of the two great circles from which all locations on the earth’s surface are referenced.locations on the earth’s surface are referenced.
23. 23. Grunt Productions 2007 Terrestrial Coordinate SystemTerrestrial Coordinate System  Small Circle: A circle formed from the intersection ofSmall Circle: A circle formed from the intersection of a plane not passing through the center of the earth.a plane not passing through the center of the earth.  Examples are Parallels of LatitudeExamples are Parallels of Latitude
24. 24. Grunt Productions 2007 Measurement of ArcMeasurement of Arc Positions in relationship to Earth’s Coordinates system arePositions in relationship to Earth’s Coordinates system are expressed in:expressed in: PRONOUNCEDPRONOUNCED SYMBOLSYMBOL DegreesDegrees (°)(°) MinutesMinutes (´)(´) SecondsSeconds (´´)(´´)
25. 25. Grunt Productions 2007 LatitudeLatitude  LatitudeLatitude - angular distance north or south between the equator and the- angular distance north or south between the equator and the parallel of a point. Latitude is measured in degrees of arc from 0parallel of a point. Latitude is measured in degrees of arc from 0°−90°°−90° either north or south of the equator.either north or south of the equator.  Latitude is measured along a meridian.Latitude is measured along a meridian.
26. 26. Grunt Productions 2007 LatitudeLatitude  Latitude is always expressed using 2 digits, e.g 49ºLatitude is always expressed using 2 digits, e.g 49º  Always given first when giving a positionAlways given first when giving a position  The length of 1 degree of latitude is always 60NMThe length of 1 degree of latitude is always 60NM
27. 27. Grunt Productions 2007 Parallels of LatitudeParallels of Latitude
28. 28. Grunt Productions 2007 Prime MeridianPrime Meridian  The meridian that passes through the original position ofThe meridian that passes through the original position of the Royal Greenwich Observatory near London,the Royal Greenwich Observatory near London, England.England.  Constitutes the second reference line for the terrestrialConstitutes the second reference line for the terrestrial coordinate system.coordinate system.
29. 29. Grunt Productions 2007 Prime MeridianPrime Meridian  All other meridians are referenced to the prime meridian;All other meridians are referenced to the prime meridian; it divides the earth into the eastern and westernit divides the earth into the eastern and western hemispheres.hemispheres.
30. 30. Grunt Productions 2007 LongitudeLongitude  Longitude - angular distance E/W between theLongitude - angular distance E/W between the prime meridian and the meridian of a point.prime meridian and the meridian of a point.  Longitude is measured in degrees of arc from 0 toLongitude is measured in degrees of arc from 0 to 180 degrees east or west of the prime meridian.180 degrees east or west of the prime meridian.  Longitude is measured along parallels of latitudeLongitude is measured along parallels of latitude
31. 31. Grunt Productions 2007 LongitudeLongitude  Longitude is always expressed using 3 digits, e.gLongitude is always expressed using 3 digits, e.g 123º.123º.  One degree of long does not equal 60 NM unlessOne degree of long does not equal 60 NM unless measured along the equator.measured along the equator.  Always given after Latitude when giving aAlways given after Latitude when giving a position.position.
32. 32. Grunt Productions 2007 Lines of Longitude
33. 33. Grunt Productions 2007
34. 34. Grunt Productions 2007 Section 3: ChartsSection 3: Charts
35. 35. Grunt Productions 2007  Desirable qualities of a chart projection:Desirable qualities of a chart projection: 1. Maintain1. Maintain true shapetrue shape of physical features.of physical features. 2. Maintain2. Maintain correct proportionscorrect proportions of features relative toof features relative to one another.one another. 3.3. True scaleTrue scale, permitting accurate measurement of, permitting accurate measurement of distance.distance. 4.4. Rhumb linesRhumb lines plot as straight lines. They are lines onplot as straight lines. They are lines on the earth’s surface that cross all meridians at thethe earth’s surface that cross all meridians at the same anglesame angle Chart ProjectionsChart Projections
36. 36. Grunt Productions 2007 Mercator ProjectionMercator Projection
37. 37. Grunt Productions 2007 ©1998GeoSystemsGlobalCorporation Mercator ProjectionMercator Projection
38. 38. Grunt Productions 2007 Mercator ProjectionMercator Projection ADVANTAGESADVANTAGES  Position, distance, and direction can be accuratelyPosition, distance, and direction can be accurately measuredmeasured  True shape of features is maintained over smallTrue shape of features is maintained over small areasareas
39. 39. Grunt Productions 2007 Chart ScaleChart Scale  The relationship between two measurements.The relationship between two measurements. Expressed as a ratio.Expressed as a ratio.  The scale to which a chart is drawn appearsThe scale to which a chart is drawn appears directly under its title.directly under its title.
40. 40. Grunt Productions 2007 Scale Conversion and ReferenceScale Conversion and Reference
41. 41. Grunt Productions 2007 Chart ScaleChart Scale  Large scale chart covers a small area and areLarge scale chart covers a small area and are used for piloting and inshore navigation.used for piloting and inshore navigation.
42. 42. Grunt Productions 2007 Chart ScaleChart Scale Small scale charts are less detailed than large scale charts and cover a large area.
43. 43. Grunt Productions 2007 Types of ChartsTypes of Charts  Coastal charts:Coastal charts: Large Scale ChartsLarge Scale Charts  1:50,000 - 1:150,0001:50,000 - 1:150,000 For approaching bays and harbors, and used forFor approaching bays and harbors, and used for coastal navigation showing outlying reefs andcoastal navigation showing outlying reefs and shoals.shoals.
44. 44. Grunt Productions 2007 Plotting a Position 1Plotting a Position 1 1. Determine the1. Determine the parallels on theparallels on the chart that bracketchart that bracket the latitude.the latitude. 2. Place the pivot2. Place the pivot point of thepoint of the compass on thecompass on the closest line.closest line.
45. 45. Grunt Productions 2007 Plotting a Position 2Plotting a Position 2 3. Spread the3. Spread the compass until thecompass until the lead rests on thelead rests on the given latitude.given latitude. 4. Move to the4. Move to the approximateapproximate longitude andlongitude and swing an arc.swing an arc.
46. 46. Grunt Productions 2007 Plotting a Position 3Plotting a Position 3 5. The same process is5. The same process is repeated using therepeated using the longitude scale and thelongitude scale and the given longitude.given longitude. 6. The desired position is6. The desired position is the intersection of thesethe intersection of these two arcs.two arcs.
47. 47. Grunt Productions 2007 Plotting a Position 4Plotting a Position 4 7. If plotted correctly, the7. If plotted correctly, the intersection should occurintersection should occur at the crest of both arcs.at the crest of both arcs.
48. 48. Grunt Productions 2007 Measuring DistanceMeasuring Distance  The latitude scale can be used to measure distances,The latitude scale can be used to measure distances, since one degree of latitude equals 60 nautical miles,since one degree of latitude equals 60 nautical miles, everywhere on the earth.everywhere on the earth.
49. 49. Grunt Productions 2007 Measuring DistanceMeasuring Distance • NEVER use the longitude scale to determine distances on a chart.
50. 50. Grunt Productions 2007 Measuring DirectionMeasuring Direction  All rhumb lines on a Mercator projection representAll rhumb lines on a Mercator projection represent truetrue directions.directions.  Measurement of directionMeasurement of direction on a Mercator chart ison a Mercator chart is accomplished by using aaccomplished by using a parallel ruler to transfer theparallel ruler to transfer the direction of a rhumb line todirection of a rhumb line to a nearby compass rose.a nearby compass rose.
51. 51. Grunt Productions 2007 Measuring DirectionMeasuring Direction • A • B 045ºTrue 060ºMagnetic
52. 52. Grunt Productions 2007 Correction of ChartsCorrection of Charts  The Hydrographer issues weekly Notices toThe Hydrographer issues weekly Notices to Mariners, which include corrections to be made toMariners, which include corrections to be made to UK charts.UK charts.  When charts are bought, they are generallyWhen charts are bought, they are generally corrected up to date.corrected up to date.  Once in use Notices to Mariners should beOnce in use Notices to Mariners should be checked and corrections to charts made aschecked and corrections to charts made as necessary.necessary.
53. 53. Grunt Productions 2007 Correction of ChartsCorrection of Charts  When a correction has been made, a note of theWhen a correction has been made, a note of the year and Notice to Mariner number should beyear and Notice to Mariner number should be made in the bottom left hand corner of the chart,made in the bottom left hand corner of the chart, having checked that the previous correction hashaving checked that the previous correction has been made.been made. 20082008 - 41- 74 - 86 - 127- 41- 74 - 86 - 127
54. 54. Grunt Productions 2007 Section 4 CompassSection 4 Compass
55. 55. Grunt Productions 2007 Types of CompassesTypes of Compasses  Magnetic CompassMagnetic Compass A compass that senses direction by interactionA compass that senses direction by interaction between its own permanent magnets and thebetween its own permanent magnets and the earth’s magnetic field.earth’s magnetic field.  Gyroscopic CompassGyroscopic Compass A electrical gyroscopic that is designed to seek trueA electrical gyroscopic that is designed to seek true northnorth
56. 56. Grunt Productions 2007 Compass RoseCompass Rose
57. 57. Grunt Productions 2007
58. 58. Grunt Productions 2007 Directional Reference SystemsDirectional Reference Systems  Directional ReferencesDirectional References  Relative BearingsRelative Bearings ((°°R) = bearings measuredR) = bearings measured with reference to the ship’s longitudinal axiswith reference to the ship’s longitudinal axis  Magnetic BearingsMagnetic Bearings ((°°M) = bearings measuredM) = bearings measured with respect to magnetic north.with respect to magnetic north.  True BearingsTrue Bearings ((°°T) = bearings measured withT) = bearings measured with respect to true of geographic north.respect to true of geographic north.
59. 59. Grunt Productions 2007 Directional Reference SystemsDirectional Reference Systems  Ship’s Head (or heading)Ship’s Head (or heading)  a special bearing denoting the direction ina special bearing denoting the direction in which the ship is pointing.which the ship is pointing.
60. 60. Grunt Productions 2007 270ºT 000ºT 090ºT 180º T True Bearings
61. 61. Grunt Productions 2007 Magnetic CompassMagnetic Compass
62. 62. Grunt Productions 2007 270ºM 000ºM 090ºM 180º M Magnetic Bearings Variation Easterly
63. 63. Grunt Productions 2007 000ºR 090º R 270ºR 180ºR Relative Bearings
64. 64. Grunt Productions 2007 Dead Ahead Starboard Beam Port Beam Right Astern Relative Bearings
65. 65. Grunt Productions 2007 Magnetic Compass Error: VariationMagnetic Compass Error: Variation  Variation isVariation is the angle between a magnetic line ofthe angle between a magnetic line of force and a geographic (true) meridian at any locationforce and a geographic (true) meridian at any location on the earth.on the earth.  Variation exists because the earth’s magnetic andVariation exists because the earth’s magnetic and geographic poles are not in the same location.geographic poles are not in the same location.
66. 66. Grunt Productions 2007 Magnetic Compass Error: VariationMagnetic Compass Error: Variation  Magnetic anomalies in the earth’s crust alsoMagnetic anomalies in the earth’s crust also contribute to variation.contribute to variation.
67. 67. Grunt Productions 2007 True North PoleMagnetic North Pole Notice that the two poles aren’t together. The magnetic compass points to the magnetic pole, and this gives us VARIATION.
68. 68. Grunt Productions 2007 Magnetic Compass Error:Magnetic Compass Error: VariationVariation  Variation also changes from year to year as theVariation also changes from year to year as the earth’s magnetic poles tend to wander.earth’s magnetic poles tend to wander.  Variation is printed inside compass roses on allVariation is printed inside compass roses on all navigation charts.navigation charts.  Always use the compass rose nearest your currentAlways use the compass rose nearest your current Dead Reckoning position.Dead Reckoning position.
69. 69. Grunt Productions 2007 Magnetic Compass Error:Magnetic Compass Error: VariationVariation • Variation changes as an observer moves alongVariation changes as an observer moves along the globe.the globe. • However, if a ship moves in such a way that theHowever, if a ship moves in such a way that the meridians remained constant, it would bemeridians remained constant, it would be moving along anmoving along an isogonic lineisogonic line - a line along- a line along which variation remains constant.which variation remains constant.
70. 70. Grunt Productions 2007 Magnetic Compass Error:Magnetic Compass Error: VariationVariation • The amount that the Variation changes annuallyThe amount that the Variation changes annually is called the Annual Change.is called the Annual Change. • The amount of Annual Change is to be foundThe amount of Annual Change is to be found on every compass rose on the chart, next to theon every compass rose on the chart, next to the Variation, and is normally expressed as 004°WVariation, and is normally expressed as 004°W 1995 (8’E)1995 (8’E).. • To calculate change in 2008, multiply 8’E byTo calculate change in 2008, multiply 8’E by 13 (years from 1995) 104’ or 1.75°E13 (years from 1995) 104’ or 1.75°E • Apply 1.75°E to Variation of 004°W = 2.25°WApply 1.75°E to Variation of 004°W = 2.25°W
71. 71. Grunt Productions 2007 Magnetic Compass Error:Magnetic Compass Error: VariationVariation
72. 72. Grunt Productions 2007 Magnetic Compass Error:Magnetic Compass Error: DeviationDeviation  This isThis is the angle between the magnetic meridian andthe angle between the magnetic meridian and the north line on the compass card.the north line on the compass card.  Deviation is caused by the interaction of the ship’sDeviation is caused by the interaction of the ship’s metallic structure, electrical systems, metallic objectsmetallic structure, electrical systems, metallic objects (such as a cell phone left close to the compass) with(such as a cell phone left close to the compass) with the earth’s magnetic field.the earth’s magnetic field.
73. 73. Grunt Productions 2007 Deviation A ship’s compass also must deal with magnetic forces from the ship itself, e.g.magnets, electrical cabling. The sum total of these forces pulls the compass slightly away from magnetic north, producing DEVIATION.
74. 74. Grunt Productions 2007 Deviation Deviation will change in size, dependant upon the course of the vessel. Swinging of the ship and proper correction using soft and/or permanent magnets , deviation can be minimized.
75. 75. Grunt Productions 2007 Compass ConversionsCompass Conversions  Compass to TrueCompass to True 1.1. C D M V T (AE)C D M V T (AE) Can Dead Men Vote Twice (at elections)?Can Dead Men Vote Twice (at elections)? 2. C A D E T2. C A D E T Compass Add East TrueCompass Add East True
76. 76. Grunt Productions 2007 Compass ConversionsCompass Conversions  Convert Compass Courses to True Courses - thisConvert Compass Courses to True Courses - this also applies to bearings, using the deviation for thealso applies to bearings, using the deviation for the vessel’s head.vessel’s head. Compass Course 145°CCompass Course 145°C Deviation 2°WDeviation 2°W Magnetic Course 143°MMagnetic Course 143°M Variation 22°EVariation 22°E True Course 165°TTrue Course 165°T
77. 77. Grunt Productions 2007 Compass ConversionsCompass Conversions  Converting True to CompassConverting True to Compass T V M D C (AW)T V M D C (AW) True Virgins Make Dull Companions (At Weddings)True Virgins Make Dull Companions (At Weddings)
78. 78. Grunt Productions 2007 Compass ConversionsCompass Conversions  Convert True Course to Compass Course - this alsoConvert True Course to Compass Course - this also applies to bearings, using the deviation for theapplies to bearings, using the deviation for the vessel’s head.vessel’s head. True Course 165°TTrue Course 165°T Variation 22°EVariation 22°E Magnetic Course 143°MMagnetic Course 143°M Deviation 2°WDeviation 2°W Compass Course 145°CCompass Course 145°C
79. 79. Grunt Productions 2007 Section 5 Navigational Aids
80. 80. Grunt Productions 2007  Navigational Aid: Any device external to a vessel orNavigational Aid: Any device external to a vessel or aircraft intended to assist in determining position andaircraft intended to assist in determining position and safe course, or to warn of dangers or obstructions.safe course, or to warn of dangers or obstructions. Significance of Navigational AidsSignificance of Navigational Aids
81. 81. Grunt Productions 2007  Navigational aids will include:Navigational aids will include: LighthousesLighthouses Transit MarksTransit Marks Leading LinesLeading Lines BuoyageBuoyage Beacons & Day MarksBeacons & Day Marks Identifiable charted objectIdentifiable charted object Navigational AidsNavigational Aids
82. 82. Grunt Productions 2007  Criteria:Criteria:  DAYTIMEDAYTIME • LocationLocation • ShapeShape • Color SchemeColor Scheme • Auxiliary featuresAuxiliary features • Special MarkingsSpecial Markings Positive Identification of NavigationPositive Identification of Navigation AidsAids  NIGHTNIGHT • Phase characteristicPhase characteristic • Period & ColorPeriod & Color
83. 83. Grunt Productions 2007  Phase CharacteristicsPhase Characteristics Chart SymbolChart Symbol MeaningMeaning FixedFixed FF Steady, unblinkingSteady, unblinking FlashingFlashing FlFl Flashes at regularFlashes at regular intervalsintervals Quick FlashQuick Flash Qk. Fl.Qk. Fl. Flash at least 60Flash at least 60 times/min.times/min. Group FlashGroup Flash Gp. Fl.Gp. Fl. Group of two orGroup of two or more flashesmore flashes Positive Identification of NavigationPositive Identification of Navigation Aids (at night)Aids (at night)
84. 84. Grunt Productions 2007  Phase CharacteristicsPhase Characteristics Chart SymbolChart Symbol MeaningMeaning Morse CodeMorse Code Mo. [A]Mo. [A] Morse alphaMorse alpha (short/long)(short/long) OccultingOcculting Occ.Occ. On longer than it’sOn longer than it’s offoff  PeriodPeriod Length in seconds of repetitionLength in seconds of repetition  Color (red, green, yellow, or white)Color (red, green, yellow, or white) Positive Identification of NavigationPositive Identification of Navigation Aids (at night)Aids (at night)
85. 85. Grunt Productions 2007 CHARACTERISTICS OF LIGHTS Flashing pattern and period (|-----|) Type AbbreviationDescription Fixed A light showing continuously and steadily F Fixed and flashing A light in which a fixed light is combined with a flashing light of higher luminous intensity F Fl Flashing A flashing light in which a flash is regularly repeated (frequency not exceeding 30 flashes per minute) Fl Group flashing A flashing light in which a group of flashes, specified in number, is regularly repeated. Fl (2) Composite group flashing A light similar to a group flashing light except that successive groups in the period have dif- ferent numbers of flashes Fl (2+1) Isophase A light in which all durations of light and darkness are equal Iso Single occulting An occulting light in which an eclipse, or shorter duration than the light, is regularly repeated. Oc Group occulting An occulting light in which a group of eclipses, specified in number, is regularly repeated. Oc (2) Quick A quick light in which a flash is regularly repeated at a rate of 60 flashes per minute Q Interrupted quick A quick light in which the sequence of flashes is interrupted by regularly repeated eclipses of constant and long duration lQ Group quick A group of 2 or more quick flashes, specified in number, which are regularly repeated. (Not used in the waters of the United States.) Q(3) Morse code A light in which lights of two clearly different durations (dots and dashes) are grouped to represent a character or characters in the Morse code. Mo (A) Alternating A light showing different colours alternately Al RW Long flashing A flashing light in which the flash is 2 seconds or longer LFl Composite group occulting A light, similar to a group occulting light, except that successive groups in a period have different numbers of eclipses Oc (2+1)
86. 86. Grunt Productions 2007 Special Purpose LightsSpecial Purpose Lights  Sector LightsSector Lights  red light used inred light used in dangerous sectorsdangerous sectors  sector limits aresector limits are expressed in degreesexpressed in degrees truetrue as observed from aas observed from a vesselvessel, not from the, not from the light!light!
87. 87. Grunt Productions 2007 Special Purpose LightsSpecial Purpose Lights  Sector LightsSector Lights
88. 88. Grunt Productions 2007  Other Navigational aids, providing they areOther Navigational aids, providing they are charted, will include:charted, will include: Other Navigational AidsOther Navigational Aids
89. 89. Grunt Productions 2007 Navigation Marks and BuoyageNavigation Marks and Buoyage
90. 90. Grunt Productions 2007 Determining the ComputedDetermining the Computed Visibility of a NavAidVisibility of a NavAid
91. 91. Grunt Productions 2007  Horizon distanceHorizon distance = the line of sight from a position= the line of sight from a position above the earth’s surface to the visual horizon.above the earth’s surface to the visual horizon.  Geographic rangeGeographic range = the maximum distance that a= the maximum distance that a light may be seen in perfect visibility by anlight may be seen in perfect visibility by an observer’s eye who is at sea level.observer’s eye who is at sea level. Determining the ComputedDetermining the Computed Visibility of a NavAidVisibility of a NavAid
92. 92. Grunt Productions 2007  Computed rangeComputed range = the distance at which a light= the distance at which a light could be seen in perfect visibility (taking intocould be seen in perfect visibility (taking into account elevation, observer’s height of eye, and theaccount elevation, observer’s height of eye, and the curvature of the earth). Computed Range =curvature of the earth). Computed Range = Horizon Distance + Geographic DistanceHorizon Distance + Geographic Distance Determining the ComputedDetermining the Computed Visibility of a NavAidVisibility of a NavAid
93. 93. Grunt Productions 2007 Determining the ComputedDetermining the Computed Visibility of a NavAidVisibility of a NavAid  Computed visibilityComputed visibility = The maximum distance at= The maximum distance at which a light can be seen in the currentwhich a light can be seen in the current meteorological conditions.meteorological conditions.
94. 94. Grunt Productions 2007 Determining the ComputedDetermining the Computed Visibility of a NavAidVisibility of a NavAid  Luminous rangeLuminous range = the maximum distance at which a= the maximum distance at which a light may be seen under under the currentlight may be seen under under the current meteorological conditions.meteorological conditions.  Nominal rangeNominal range = a special case of the luminous= a special case of the luminous range. It is the distance a light could be seen inrange. It is the distance a light could be seen in “clear” weather. Also called the charted range.“clear” weather. Also called the charted range.
95. 95. Grunt Productions 2007
96. 96. Grunt Productions 2007 Section 6 Position Lines and FixesSection 6 Position Lines and Fixes
97. 97. Grunt Productions 2007 Position LinesPosition Lines •Position Lines (P/L) - A single observation that does not establish a fix, but does mean that ship’s position is somewhere along that line. •Label - After the position line is drawn from a charted object, a four digit time must be written above and parallel to the position line.
98. 98. Grunt Productions 2007 Position LinesPosition Lines •All Compass bearings that are to be plotted on the chart, must be corrected to True Bearings, allowing for any compass error, including deviation and variation, before plotting. •All True bearings/ courses taken from the chart, must be corrected for any compass error to obtain Compass Bearings/compass before use on radar or vessel’s magnetic compass.
99. 99. Grunt Productions 2007 Sources of Position LinesSources of Position Lines  A visual position line can be taken, using chartedA visual position line can be taken, using charted fixed navigational aids such as tanks, water towers,fixed navigational aids such as tanks, water towers, church steeples, spires, radio and TV towers, daychurch steeples, spires, radio and TV towers, day marks, fixed navigation lights, flagpoles, or tangentsmarks, fixed navigation lights, flagpoles, or tangents to points of land.to points of land.  In general fixing off floating objects, especiallyIn general fixing off floating objects, especially buoys, should be avoided, if there are fixed chartedbuoys, should be avoided, if there are fixed charted objects available.objects available.
100. 100. Grunt Productions 2007 VisualVisual PositionPosition LineLine 1000
102. 102. Grunt Productions 2007 Position Line MeasurementPosition Line Measurement  Visual Bearings can be measured in:Visual Bearings can be measured in: 1. Degrees Relative ( # # #1. Degrees Relative ( # # # 00 R )R ) 2. Degrees per Gyro Compass ( # # # ºG )2. Degrees per Gyro Compass ( # # # ºG ) 3. Degrees Magnetic ( # # #3. Degrees Magnetic ( # # # 00 M )M )  The navigator must convert any of these types ofThe navigator must convert any of these types of bearings to True before they can be plotted on thebearings to True before they can be plotted on the chart.chart. Degrees True ( # # #Degrees True ( # # # 00 T)T)
103. 103. Grunt Productions 2007 Plotting and Labeling a FixPlotting and Labeling a Fix •Fix - The point where two or more position lines, taken at the same time, cross. This indicates the ship’s position on the chart. •Label - Use the four digit time next to the fix,it should be parallel to the bottom of the chart. The times of the individual position lines are not written.
104. 104. Grunt Productions 2007 VisualVisual PositionPosition Fix 1Fix 1 Compass bearing of Abode Island bearing 009°Compass, deviation 1ºW, variation 23ºE, gives 030 º True Bearing
105. 105. Grunt Productions 2007 VisualVisual PositionPosition Fix 2Fix 2 Compass bearing of Grebe Island Light bearing 058 º Compass, deviation 1ºW, variation 23ºE, gives 080 º True Bearing
106. 106. Grunt Productions 2007 VisualVisual PositionPosition Fix 3Fix 3 Compass bearing of Pt. Atkinson Light bearing 098ºCompass, deviation 1ºW, variation 23º E, gives True Bearing of 120 º T
107. 107. Grunt Productions 2007 VisualVisual PositionPosition Fix 4Fix 4 1230 Insert fix circle on intersection of position lines, and time of fix
108. 108. Grunt Productions 2007 Cocked HatsCocked Hats •In a perfect world, with due allowance made for compass error, the three position lines will cross at one point. •However depending on the speed of the vessel, the proximity of the object from which a vessel is being fixed, and the accuracy of the bearing when taken, and other factors, it is far more likely that a cocked hat will be obtained. •The larger the cocked hat, the larger an error on one, two or all of the position lines is likely to be.
109. 109. Grunt Productions 2007 CockedCocked HatHat 1230 In this example there is an error of 3ºE on the compass bearing of Point Atkinson Light and a cocked hat is formed.
110. 110. Grunt Productions 2007 Cocked HatsCocked Hats • Where a plotted position is a cocked hat, and there is no obvious error (such as in calculation), it should be generally assumed the position of the vessel is the point in the cocked hat closest to the nearest danger. •Another position should be taken a soon as convenient to check on the position.An
111. 111. Grunt Productions 2007 Reducing ErrorsReducing Errors • When taking distances or ranges, always take the ranges ahead or astern first, to minimize errors (as these ranges will change quickest with the speed of the vessel) before taking ranges on the beam. •When taking compass bearings, always take the bearings on the beam first, to minimize errors (as these bearings will change quickest with the speed of the vessel) before taking bearings ahead or astern.
112. 112. Grunt Productions 2007 Radar FixesRadar Fixes • Radar bearings are subject to compass error. • Therefore the best way to obtain a fix by radar, is to take three radar distances off charted and identified objects.
113. 113. Grunt Productions 2007 RadarRadar Position 1Position 1 Using radar: Grebe Is Electronic Bearing Marker showing 058 º M Variable Range Marker showing 0.82’
114. 114. Grunt Productions 2007 RadarRadar Position 2Position 2 From radar, plot position circle: Grebe Is Distance 0.49 nm
115. 115. Grunt Productions 2007 RadarRadar Position 3Position 3 Grebe Is Range 0.82’ A second range of 0.93’ off Eagle Is. would give fix Mark fix position and time. Best fix would be have third range. 1000
116. 116. Grunt Productions 2007 RadarRadar Position 4Position 4 Radar bearing of Grebe Is. is 058 º compass Deviation 1ºW Variation 23ºE True Bearing 080 ºT which confirms ranges 1000
117. 117. Grunt Productions 2007 Electronic PositionElectronic Position • The GPS can give an accurate electronic position. •First check that the GPS information is live, and not on Dead Reckoning (which GPS reverts to with certain faults). •Also check that the HDOP figure is low - 1 is best.
118. 118. Grunt Productions 2007 ElectronicElectronic Position 1Position 1 Note down Latitude and Longitude 49º 20.38’N 123º 17.23’W
119. 119. Grunt Productions 2007 ElectronicElectronic Position 2Position 2 Plot Latitude and Longitude 49º 20.38’N 123º 17.23’W
120. 120. Grunt Productions 2007 ElectronicElectronic Position 3Position 3 1000 Insert fix symbol, and time
121. 121. Grunt Productions 2007 TransitsTransits
122. 122. Grunt Productions 2007 TransitsTransits  Transits are the most accurate type of position line,Transits are the most accurate type of position line, when two charted objects line up.when two charted objects line up.  Transits are one of the most valuable tools whenTransits are one of the most valuable tools when close to dangers or the land.close to dangers or the land.  Some transits are man made (intentional) and othersSome transits are man made (intentional) and others are natural (coincidental).are natural (coincidental).
123. 123. Grunt Productions 2007 TransitsTransits  The main benefits of transits are:The main benefits of transits are: 1. There is no compass deviation or variation.1. There is no compass deviation or variation. 2. They can be used when the vessel's motion interferes2. They can be used when the vessel's motion interferes with the use of a compass.with the use of a compass. 3. They are instantaneous and can be monitored3. They are instantaneous and can be monitored continuously.continuously. 4.They occur frequently when in confined waters.4.They occur frequently when in confined waters.
124. 124. Grunt Productions 2007 TransitsTransits •Good transit - Beacon in line with lighthouse
125. 125. Grunt Productions 2007 TransitsTransits •Poor transit - Buoy in line with end of land. This may be inaccurate due to land changing due to tidal height and the buoy being set by tidal stream or current.
126. 126. Grunt Productions 2007 TransitsTransits 0945A transit can give either a position line, or as shown, a heading to steer on from the northwest, before altering to about 045°T into Fisherman's Cove
127. 127. Grunt Productions 2007 Symbol Type Meaning Labeling Fixes Fix Fix DR EP Accurate Visual Fix Accurate Fix obtained by electronic means Dead reckon position, advanced from previous fix. Estimated position. Most probable position of ship.
128. 128. Grunt Productions 2007 Dead ReckoningDead Reckoning • Dead Reckoning is the process of determining a ship’s approximate position by applying, from its last known position, a vector or a series of consecutive vectors representing the true courses steered and the distances run as determined by the ship’s speed and time, without considering the effects of wind and current. • From a known ship’s position, predicted future positions are plotted.
129. 129. Grunt Productions 2007 DeadDead ReckoningReckoning 1230 DR 1245 From ship’s known position at 1230, a future position is plotted for 1245, knowing vessel’s course and speed.
130. 130. Grunt Productions 2007 Dead ReckoningDead Reckoning • Dead Reckoning is derived from DEDUCED, or DED, reckoning which was the process by which a vessel’s position was computed trigonometrically in relation to a known point of departure.
131. 131. Grunt Productions 2007 EstimatedEstimated PositionPosition 1230 EP 1245 From ship’s known position at 1230, a future position is plotted for 1245, knowing vessel’s course and speed, and allowing for set and drift of tide.
132. 132. Grunt Productions 2007 Parallel IndexingParallel Indexing
133. 133. Grunt Productions 2007 Parallel IndexingParallel Indexing • Parallel indexing is using the radar to monitor the track of a vessel along a preplanned course, maintaining a distance off a known charted object. • Where using a magnetic compass input to a radar, the true bearing will have to be corrected for variation and deviation before setting the Electronic Bearing Marker.
134. 134. Grunt Productions 2007 ParallelParallel IndexingIndexing CIR 0.32’ 015ºT Find a radar conspicuous object on the chart. Draw a line parallel to the required course touching the object. Measure the distance between the course line and the parallel index line. That is the Cross Index range.
135. 135. Grunt Productions 2007 ParallelParallel IndexingIndexing Offset and set up the Variable Range Marker to the distance off a conspicuous point of land that is required, and set the Electronic Bearing Marker to the required compass course. Course 017°C VRM 0.18nm EBL 017°C
136. 136. Grunt Productions 2007 ParallelParallel IndexingIndexing The VRM should run up the EBL if the vessel is staying on track. Course 017°C VRM 0.18nm EBL 017°C
137. 137. Grunt Productions 2007 Time-Speed-Distance CalculationsTime-Speed-Distance Calculations
138. 138. Grunt Productions 2007 Time-Speed-Distance CalculationsTime-Speed-Distance Calculations • These calculations can be made using a nautical slide rule, electronic calculator, set of pre-computed tables, or the speed nomogram. D = S x T where: D = distance traveled note: ( 1 nm = 2000 yds) S = speed in knots(nautical miles per hour) T = time in hours
139. 139. Grunt Productions 2007  3 Minute Rule3 Minute Rule Distance traveled in 3 minutes (yards) =Distance traveled in 3 minutes (yards) = Ship’s speed (knots) X 100Ship’s speed (knots) X 100  6 Minute Rule6 Minute Rule Distance traveled in 6 minutes (nm) =Distance traveled in 6 minutes (nm) = Ship’s Speed (knots) divided by 10.Ship’s Speed (knots) divided by 10. Simple RulesSimple Rules
140. 140. Grunt Productions 2007 Section 7: TidesSection 7: Tides
141. 141. Grunt Productions 2007 Tides DefinedTides Defined  Tides are theTides are the verticalvertical rise and fall of the ocean level duerise and fall of the ocean level due to the gravitational and centrifugal forces between theto the gravitational and centrifugal forces between the earth and the moon, and to a lesser extent, the sun.earth and the moon, and to a lesser extent, the sun.
142. 142. Grunt Productions 2007 Spring TidesSpring Tides  When the tidal effects of the sun and the moonWhen the tidal effects of the sun and the moon act in concert.act in concert.
143. 143. Grunt Productions 2007 Neap TidesNeap Tides  When the tidal effects of the sun and the moon are inWhen the tidal effects of the sun and the moon are in opposition to one another.opposition to one another.
144. 144. Grunt Productions 2007 Tidal Reference PlanesTidal Reference Planes  Mean high-water springs (MHWS)Mean high-water springs (MHWS)  average height of all spring tide high-water levelsaverage height of all spring tide high-water levels  Mean higher high water (MHHW)Mean higher high water (MHHW)  average of the higher of the high-water levels each tidal day,average of the higher of the high-water levels each tidal day, 19-year period19-year period  Mean high water (MHW)Mean high water (MHW)  average of all high-tide water levels, 19-year periodaverage of all high-tide water levels, 19-year period  Mean high-water neaps (MHWN)Mean high-water neaps (MHWN)  average recorded height of all neap tide high-water levelsaverage recorded height of all neap tide high-water levels
145. 145. Grunt Productions 2007 Tidal Reference PlanesTidal Reference Planes  Mean low-water neaps (MLWN)Mean low-water neaps (MLWN)  average recorded height of all neap tide high-water levelsaverage recorded height of all neap tide high-water levels  Mean low water (MLW)Mean low water (MLW)  average of all low-tide water levels, 19-year periodaverage of all low-tide water levels, 19-year period  Mean lower low water (MLLW)Mean lower low water (MLLW)  average of the lower of the low-water levels each tidal day,average of the lower of the low-water levels each tidal day, 19-year period19-year period  Mean low water springs (MLWS)Mean low water springs (MLWS)  average of all spring tide low-water levelsaverage of all spring tide low-water levels
146. 146. Grunt Productions 2007 Tidal Reference PlanesTidal Reference Planes Height marked on chart Depth marked on chart
147. 147. Grunt Productions 2007 Tidal PatternsTidal Patterns  In general in most of the world, the tides go up andIn general in most of the world, the tides go up and down on a semi diurnal curvedown on a semi diurnal curve
148. 148. Grunt Productions 2007 Tidal Patterns - SemidiurnalTidal Patterns - Semidiurnal
149. 149. Grunt Productions 2007 Tidal Patterns - DiurnalTidal Patterns - Diurnal
150. 150. Grunt Productions 2007 Calculating Rise of TideCalculating Rise of Tide  Q. If a low water was at 0600, with a height of 0.2Q. If a low water was at 0600, with a height of 0.2 meters, and the next high water was at 1200 , with ameters, and the next high water was at 1200 , with a height of 5.6 meters, what would be the approximateheight of 5.6 meters, what would be the approximate rise of tide and therefore approximate height of tide ifrise of tide and therefore approximate height of tide if your vessel was setting out at 0900.your vessel was setting out at 0900.
151. 151. Grunt Productions 2007 Calculating Rise and Height of TideCalculating Rise and Height of Tide A.A. 1200 LT High water 5.6 m1200 LT High water 5.6 m 0600 LT Low water 0.2 m0600 LT Low water 0.2 m 6.00hrs Range 5.4 m6.00hrs Range 5.4 m 0900 LT0900 LT 0600 LT Low water 0.2 m0600 LT Low water 0.2 m 3.00 hrs3.00 hrs Approximate rise of tide is (3hrs/6hrs) x 5.4m = 2.7 mApproximate rise of tide is (3hrs/6hrs) x 5.4m = 2.7 m Approximate height of tide above chart datum, if your vessel wasApproximate height of tide above chart datum, if your vessel was setting out at 0900 would be : Ht of LW (0.2m) +setting out at 0900 would be : Ht of LW (0.2m) + rise of tide (2.7m) = 2.9 m.rise of tide (2.7m) = 2.9 m.
152. 152. Grunt Productions 2007 Calculating Rise of TideCalculating Rise of Tide  In this case allow only 2.5 meters. Always allow lessIn this case allow only 2.5 meters. Always allow less rise of tide close to low water due to the rate ofrise of tide close to low water due to the rate of change of height being least close to time of lowchange of height being least close to time of low water (and high water).water (and high water).
153. 153. Grunt Productions 2007
154. 154. Grunt Productions 2007 Section 8 Ocean CurrentsSection 8 Ocean Currents
155. 155. Grunt Productions 2007 Ocean CurrentsOcean Currents  Giant patterns of rotation “gyres” in each of theGiant patterns of rotation “gyres” in each of the major ocean basins.major ocean basins.  Caused by natural effects: salinity,Caused by natural effects: salinity, temperature, the Coriolis Effect, etc.temperature, the Coriolis Effect, etc.  Described in the Sailing DirectionsDescribed in the Sailing Directions  Examples are the Gulf Stream, the Kuro ShioExamples are the Gulf Stream, the Kuro Shio and the Owa Shioand the Owa Shio
156. 156. Grunt Productions 2007 Ocean CurrentsOcean Currents
157. 157. Grunt Productions 2007 Ocean CurrentsOcean Currents
158. 158. Grunt Productions 2007 Tidal CurrentsTidal Currents
159. 159. Grunt Productions 2007 Tidal CurrentsTidal Currents
160. 160. Grunt Productions 2007 Tidal CurrentsTidal Currents  Caused by the rise and fall of tides in coastalCaused by the rise and fall of tides in coastal waters.waters.  Speed and timing is dependent upon whether itSpeed and timing is dependent upon whether it is spring or neap tides, and the shape of theis spring or neap tides, and the shape of the coast and the sea floor.coast and the sea floor.
161. 161. Grunt Productions 2007 Tidal CurrentsTidal Currents
162. 162. Grunt Productions 2007 Relationship of TermsRelationship of Terms  Flood CurrentFlood Current  A tidal current that flows towards shoreA tidal current that flows towards shore (follows a low tide).(follows a low tide).
163. 163. Grunt Productions 2007 Relationship of TermsRelationship of Terms  Ebb CurrentEbb Current  A tidal current that flows away from shoreA tidal current that flows away from shore (follows a high tide).(follows a high tide).
164. 164. Grunt Productions 2007 Relationship of TermsRelationship of Terms  Slack WaterSlack Water  A period where there is no horizontalA period where there is no horizontal movement of water. Corresponds to themovement of water. Corresponds to the “stand” of the tide.“stand” of the tide.
165. 165. Grunt Productions 2007 Set and DriftSet and Drift  Set: the direction of the current pushing;Set: the direction of the current pushing; normally expressed innormally expressed in oo T.T.  Drift: the speed of the water, normallyDrift: the speed of the water, normally expressed in knots.expressed in knots.  Set and drift combined describe the current.Set and drift combined describe the current.
166. 166. Grunt Productions 2007 WavesWaves
167. 167. Grunt Productions 2007 WavesWaves • If the wind is blowing from the water onto theIf the wind is blowing from the water onto the land they are onshore winds. This causesland they are onshore winds. This causes waves to break a little earlier, thus pushingwaves to break a little earlier, thus pushing them over.them over.
168. 168. Grunt Productions 2007 WavesWaves • If the wind blows from the land out to sea,If the wind blows from the land out to sea, they are offshore winds. They blow againstthey are offshore winds. They blow against the incoming swell and sustain the wavesthe incoming swell and sustain the waves from breaking while they jack up a little higherfrom breaking while they jack up a little higher and steeper before they break.and steeper before they break.
169. 169. Grunt Productions 2007 SwellSwell
170. 170. Grunt Productions 2007 SwellSwell  Most of the swells on the British coast areMost of the swells on the British coast are generated by storms that start in the Atlantic andgenerated by storms that start in the Atlantic and spin up the coast of Europe all year.spin up the coast of Europe all year.
171. 171. Grunt Productions 2007 SwellSwell
172. 172. Grunt Productions 2007 SwellSwell  This forces the water up and sort of trips theThis forces the water up and sort of trips the wave and it breaks, the top of the wave fallswave and it breaks, the top of the wave falls down in front of itself.down in front of itself.
173. 173. Grunt Productions 2007 Rip CurrentsRip Currents
174. 174. Grunt Productions 2007 Rip CurrentsRip Currents  A Rip Current is a current of water flowing out toA Rip Current is a current of water flowing out to sea.sea.  Rips form when waves push large volumes ofRips form when waves push large volumes of water onto the shore and the water returnswater onto the shore and the water returns seaward thorough channels between sand bars,seaward thorough channels between sand bars, behind islands and around rocky headlands.behind islands and around rocky headlands.
175. 175. Grunt Productions 2007 Rip CurrentsRip Currents  On a sea coast, they can be identified by a lineOn a sea coast, they can be identified by a line of discolored water, foam and debris floatingof discolored water, foam and debris floating seaward or an area of choppy or confused waterseaward or an area of choppy or confused water in the swell.in the swell.
176. 176. Grunt Productions 2007 Rip CurrentsRip Currents
177. 177. Grunt Productions 2007 Local KnowledgeLocal Knowledge  On all voyages, observe local currents andOn all voyages, observe local currents and waves, what direction they flow at what times,waves, what direction they flow at what times, where the areas.where the areas.  This will assist in:This will assist in: 1. Plotting the best course in certain weathers.1. Plotting the best course in certain weathers.
178. 178. Grunt Productions 2007 Section 9 WeatherSection 9 Weather
179. 179. Grunt Productions 2007 Atmospheric PressureAtmospheric Pressure
180. 180. Grunt Productions 2007 Atmospheric PressureAtmospheric Pressure •The standard atmosphere (symbol: atm) is a unit of pressure and is defined as being precisely equal to 101.325 kilopascals, 1013.25 millibars, or 29.92 inches of mercury. •The pressure gradient between a high pressure area and a low pressure area governs the strength of the wind, the wind blowing from high pressure to low pressure. •The greater the gradient the stronger the wind.
181. 181. Grunt Productions 2007 Atmospheric PressureAtmospheric Pressure •An extreme example is the centre of a hurricane which can go as low as 94.8 kilopascals. The pressure gradient is huge, causing the winds to blow at 100 to 150 knots (nautical miles per hour).
182. 182. Grunt Productions 2007 Mean Sea Level PressureMean Sea Level Pressure 15 year average Mean Sea Level Pressure for June July August 15 year average Mean Sea Level Pressure for December January February
183. 183. Grunt Productions 2007 GlobalGlobal CirculationCirculation  The Earth rotates at a constant rate, and theThe Earth rotates at a constant rate, and the winds blow, the transfer of momentum betweenwinds blow, the transfer of momentum between Earth/atmosphere /Earth must be in balance;Earth/atmosphere /Earth must be in balance; and the angular velocity of the systemand the angular velocity of the system maintained.maintained.  The atmosphere is rotating in the same directionThe atmosphere is rotating in the same direction as the Earth but westerly winds move faster andas the Earth but westerly winds move faster and easterly winds move slower than the Earth'seasterly winds move slower than the Earth's surface.surface.
184. 184. Grunt Productions 2007 Global CirculationGlobal Circulation Remember winds are identified by the directionRemember winds are identified by the direction they are coming from, not heading to!they are coming from, not heading to!
185. 185. Grunt Productions 2007 Weather FrontsWeather Fronts •Where air masses meet, there are well- marked boundary zones called fronts. This is where most cloud and precipitation occurs. •In the northern hemisphere the circulation is anticlockwise around low pressure and clockwise around high pressure. The air flows almost parallel to the isobars but actually 10-15 degrees inwards towards the low pressure.
186. 186. Grunt Productions 2007 Weather FrontsWeather Fronts • There are three types of front: 1. Warm front 2. Cold front 3. Occlusions and Occluded Fronts
187. 187. Grunt Productions 2007 Warm FrontsWarm Fronts •When a warm moist air mass rises above a cold air mass, a warm front forms. The gradient of the front is very shallow. Warm fronts occur at the forward edge of a depression (a low- pressure system).
188. 188. Grunt Productions 2007 Warm FrontsWarm Fronts
189. 189. Grunt Productions 2007 Warm FrontsWarm Fronts Weather Phenomenon Prior to the Passing of the Front Contact with the Front After the Passing of the Front Temperature Cool Warming suddenly Warmer then leveling off Atmospheric Pressure Decreasing steadily Levelling off Slight rise followed by a decrease Winds S to SE Variable S to SW Precipitation Showers, snow, sleet or drizzle Light Drizzle None Clouds Cirrus, cirrostratus, altostratus, nimbostratus, and then stratus Stratus, sometimes cumulonimbus Clearing with scattered stratus, sometimes scattered cumulonimbus
190. 190. Grunt Productions 2007 Cold FrontsCold Fronts
191. 191. Grunt Productions 2007 Cold FrontsCold Fronts Weather Phenomenon Prior to the Passing of the Front Contact with the Front After the Passing of the Front Temperature Warm Cooling suddenly Cold and getting colder Atmospheric Pressure Decreasing Steadily Levelling off then increasing Increasing steadily Winds S to SE Variable and Gusty W to NW Precipitation Showers Heavy rain or snow, sometimes hail Showers then clearing Clouds Cirrus and cirrostratus, changing later to cumulus and cumulonimbus Cumulus and cumulonimbus Cumulus
192. 192. Grunt Productions 2007 Cold FrontsCold Fronts A cold front marks the advance of colder air undercutting warm air. The gradient of the cold front is steeper than that of a warm front, and the rainfall is usually heavier. Thunderstorms sometimes form along a cold front.
193. 193. Grunt Productions 2007 Occluded FrontsOccluded Fronts •Depressions and other frontal systems have a three-dimensional structure. •Most depressions weaken when the cold front catches up with the warm front and cuts it off from the ground. •If the cold front rises over the warm front, this is a warm occlusion. •If the cold front undercuts the warm front this is a cold occlusion.
194. 194. Grunt Productions 2007 Occluded FrontsOccluded Fronts • Weather systems grow mature and decay and as they do, new ones are created. This creates families of weather systems.
195. 195. Grunt Productions 2007 Wind
196. 196. Grunt Productions 2007 WindWind Wind is primarily the result of uneven heating of the earth’s surface, which causes large hotter areas and large cooler areas.
197. 197. Grunt Productions 2007 Wind ForceWind Force FORCE EQUIVALENT SPEED DESCRIPTION SPECIFICATIONS FOR USE AT SEA 10 m above ground miles/hour knots 0 0-1 0-1 Calm Sea like a mirror
198. 198. Grunt Productions 2007 Wind ForceWind Force FORCE EQUIVALENT SPEED DESCRIPTION SPECIFICATIONS FOR USE AT SEA 10 m above ground miles/hour knots 1 1-3 1-3 Light air Ripples with the appearance of scales are formed, but without foam crests.
199. 199. Grunt Productions 2007 Wind ForceWind Force FORCE EQUIVALENT SPEED DESCRIPTION SPECIFICATIONS FOR USE AT SEA 10 m above ground miles/hour knots 2 4-7 4-6 Light Breeze Small wavelets, still short, but more pronounced. Crests have a glassy appearance and do not break.
200. 200. Grunt Productions 2007 Wind ForceWind Force FORCE EQUIVALENT SPEED DESCRIPTION SPECIFICATIONS FOR USE AT SEA 10 m above ground miles/hour knots 3 8-12 7-10 Gentle Breeze Large wavelets. Crests begin to break. Foam of glassy appearance. Perhaps scattered white horses.
201. 201. Grunt Productions 2007 Wind ForceWind Force FORCE EQUIVALENT SPEED DESCRIPTION SPECIFICATIONS FOR USE AT SEA 10 m above ground miles/hour knots 4 13-18 11-16 Moderate Breeze Small waves, becoming larger; fairly frequent white horses.
202. 202. Grunt Productions 2007 Wind ForceWind Force FORCE EQUIVALENT SPEED DESCRIPTION SPECIFICATIONS FOR USE AT SEA 10 m above ground miles/hour knots 5 19-24 17-21 Fresh Breeze Moderate waves, taking a more pronounced long form; many white horses are formed. Chance of some spray.
203. 203. Grunt Productions 2007 Wind ForceWind Force FORCE EQUIVALENT SPEED DESCRIPTION SPECIFICATIONS FOR USE AT SEA 10 m above ground miles/hour knots 6 25-31 22-27 Strong Breeze Large waves begin to form; the white foam crests are more extensive everywhere. Probably some spray.
204. 204. Grunt Productions 2007 Wind ForceWind Force FORCE EQUIVALENT SPEED DESCRIPTION SPECIFICATIONS FOR USE AT SEA 10 m above ground miles/hour knots 7 32-38 28-33 Near Gale Sea heaps up and white foam from breaking waves begins to be blown in streaks along the direction of the wind.
205. 205. Grunt Productions 2007 Wind ForceWind Force FORCE EQUIVALENT SPEED DESCRIPTION SPECIFICATIONS FOR USE AT SEA 10 m above ground miles/hour knots 8 39-46 34-40 Gale Moderately high waves of greater length; edges of crests begin to break into spindrift. The foam is blown in well-marked streaks along the direction of the wind.
206. 206. Grunt Productions 2007 Wind ForceWind Force FORCE EQUIVALENT SPEED DESCRIPTION SPECIFICATIONS FOR USE AT SEA 10 m above ground miles/hour knots 9 47-54 41-47 Severe Gale High waves. Dense streaks of foam along the direction of the wind. Crests of waves begin to topple, tumble and roll over. Spray may affect visibility.
207. 207. Grunt Productions 2007 Wind ForceWind Force FORCE EQUIVALENT SPEED DESCRIPTION SPECIFICATIONS FOR USE AT SEA 10 m above ground miles/hour knots 10 55-63 48-55 Storm Very high waves with long over- hanging crests. The resulting foam, in great patches, is blown in dense white streaks along the direction of the wind. On the whole the surface of the sea takes on a white appearance. The 'tumbling' of the sea becomes heavy and shock-like. Visibility affected.
208. 208. Grunt Productions 2007 Wind ForceWind Force FORCE EQUIVALENT SPEED DESCRIPTION SPECIFICATIONS FOR USE AT SEA 10 m above ground miles/hour knots 11 64-72 56-63 Violent Storm Exceptionally high waves (small and medium-size ships might be for a time lost to view behind the waves). The sea is completely covered with long white patches of foam lying along the direction of the wind. Everywhere the edges of the wave crests are blown into froth. Visibility affected.
209. 209. Grunt Productions 2007 Wind ForceWind Force FORCE EQUIVALENT SPEED DESCRIPTION SPECIFICATIONS FOR USE AT SEA 10 m above ground miles/hour knots 12 73-83 64-71 Hurricane The air is filled with foam and spray. Sea completely white with driving spray; visibility very seriously affected.
210. 210. Grunt Productions 2007 Sea BreezeSea Breeze •A sea-breeze (or onshore breeze) is a wind from the sea that develops over land near coasts. •It is formed by increasing temperature differences between the land (which heats up faster) and water (which warms slower) which create a pressure minimum over the land due to its relative warmth and forces higher pressure, cooler air from the sea to move inland.
211. 211. Grunt Productions 2007 Sea BreezeSea Breeze It generally occurs in the afternoon.
212. 212. Grunt Productions 2007 Land BreezeLand Breeze •A land-breeze (or offshore breeze) is a wind to the sea that develops over land near coasts. • It is formed by increasing temperature differences between the land (which cools faster) and water (which cools slower) which create a pressure minimum over the sea due to its relative warmth and forces higher pressure, cooler air from the land to move offshore.
213. 213. Grunt Productions 2007 Land BreezeLand Breeze It generally occurs in the very early morning.
214. 214. Grunt Productions 2007 Katabatic WindsKatabatic Winds •A katabatic wind, from the Greek word katabatikos meaning "going downhill", is a wind that blows down a topographic incline such as a hill, mountain, or glacier. •The cold form of katabatic wind originates in a cooling, either radiatively or through vertical motion, of air at the top of the mountain, glacier, or hill.
215. 215. Grunt Productions 2007 Katabatic WindsKatabatic Winds •Since the density of air increases with lower temperature, the air will flow downwards, warming adiabatically as it descends, but still remaining relatively cold.
216. 216. Grunt Productions 2007 Wind Force & Sea StateWind Force & Sea State •The visible effects of the wind on the sea will be modified by the relative directions of wind and tide. •If the wind and tide are in opposite directions, then a larger chop will be created, giving the impression of the wind being stronger. •If wind and tide are in the same direction, the amount of sea will be reduced, giving the impression of the wind being less.
217. 217. Grunt Productions 2007 Sea and SwellSea and Swell •Sea is the effect of wind passing over the water locally. •Swell is only found in the open ocean and will be effects of weather systems, hundreds of miles away.
218. 218. Grunt Productions 2007 Fog
219. 219. Grunt Productions 2007 FogFog
220. 220. Grunt Productions 2007 FogFog • Fog is a cloud in contact with the ground. • Fog differs from other clouds only in that fog touches the surface of the Earth. • The same cloud that is not fog on lower ground may be fog where it contacts higher ground such as hilltops or mountain ridges. • Fog is distinct from mist only in its density.
221. 221. Grunt Productions 2007 FogFog • Fog is defined as cloud which reduces visibility to less than 1 nautical mile, where as mist is that which reduces visibility to more than 1 nautical mile.
222. 222. Grunt Productions 2007 FogFog •Fog forms when water vapor in the air at the surface begins to condense into liquid water. •Fog normally occurs at a relative humidity of 100%. This can be achieved by either adding moisture to the air or dropping the ambient air temperature. •Fog can form at lower humidities, and fog can sometimes not form with relative humidity at 100%.
223. 223. Grunt Productions 2007 FogFog •Advection fog occurs when moist air passes over a cool surface by advection (wind) and is cooled. It is common as a warm front passes over an area significantly cooler. It's most common at sea when tropical air encounters cooler waters, or in areas of upwelling.
224. 224. Grunt Productions 2007 Upslope FogUpslope Fog
225. 225. Grunt Productions 2007 Other Types of FogOther Types of Fog
226. 226. Grunt Productions 2007 FogFog “Slight Sea, Low Swell, Cloudy, Fine and Clear”“Slight Sea, Low Swell, Cloudy, Fine and Clear”
227. 227. Grunt Productions 2007 Precipitation
228. 228. Grunt Productions 2007 Orographic RainOrographic Rain •Orographic rain (or relief rain) is caused when the warm moisture-laden wind blowing in to the land from the sea encounters a natural barrier such as mountains. This forces the wind to rise. •With gain in altitude, the air expands dynamically due to a decrease in air pressure. •Due to this the wind experiences a decrease in temperature, which results in the increase of the relative humidity.
229. 229. Grunt Productions 2007 Orographic RainOrographic Rain •This causes condensation of the water vapor into water droplets to form clouds. •The relative humidity continues to increase until the dewpoint reaches the level of condensation, causing air to be saturated. •This height where the condensation occurs is called the level of condensation. •When the cloud droplets become too heavy to be suspended, rain falls.
230. 230. Grunt Productions 2007 Orographic RainOrographic Rain
231. 231. Grunt Productions 2007
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