Marine Charts andMarine Charts andNavigationNavigation

OceanographyOceanography

20142014

Earth Coordinate SystemEarth Coordinate System

► LatitudeLatitude

1.1. Parallels of arcParallels of arc

2.2. 0º-90º N-S from 0º-90º N-S from the equator to the equator to polespoles

3.3. 1º = 60’ (1’=60 1º = 60’ (1’=60 sec)sec)

4.4. small circlessmall circles

► LongitudeLongitude

1.1. Meridians of angleMeridians of angle

2.2. 0º (prime 0º (prime meridian) -180º E-meridian) -180º E-W pole to poleW pole to pole

3.3. Prime meridian is Prime meridian is measured at measured at Greenwich EnglandGreenwich England

4.4. great circlesgreat circles

Marine ChartsMarine Charts

► Water depthsWater depths► Configuration of the shoreline in Configuration of the shoreline in

coastal waterscoastal waters► Navigational lights, buoys, landmarksNavigational lights, buoys, landmarks► Chart title blockChart title block► Nature of the bottom (hrd, rky, g, sh, Nature of the bottom (hrd, rky, g, sh,

s, co)s, co)► North is the top, latitude scale on North is the top, latitude scale on

side, and longitude on top and side, and longitude on top and bottombottom

► Many charts cover less than a 1º of Many charts cover less than a 1º of lat or long, so be careful when lat or long, so be careful when “fixing” a position“fixing” a position

Units of DistanceUnits of Distance

► Statute vs. nautical milesStatute vs. nautical miles► 1 nautical mile = 1’ of latitude1 nautical mile = 1’ of latitude► 1 nautical mile = 1.15 statute miles1 nautical mile = 1.15 statute miles► 1º of latitude = 60’ = 60 nautical miles1º of latitude = 60’ = 60 nautical miles► 1º = 60 nautical miles = 69 statute miles1º = 60 nautical miles = 69 statute miles► Use a drafting compass or dividers and spread points to apply to chart bar scale to Use a drafting compass or dividers and spread points to apply to chart bar scale to

determine distancedetermine distance

Units of SpeedUnits of Speed

► Knot = 1 nautical Knot = 1 nautical mile/hourmile/hour

► 1 knot x 1.85 = 1 knot x 1.85 = km/hrkm/hr

Plotting a CoursePlotting a Course

► Magnetic vs. true (geographic) NorthMagnetic vs. true (geographic) North► Use the “Compass rose” on the chartUse the “Compass rose” on the chart► The compass is graduated from 0º-360º and The compass is graduated from 0º-360º and

broken into 32 points on the compassbroken into 32 points on the compass► Cardinal points (0, 90, 180, 270 degrees)Cardinal points (0, 90, 180, 270 degrees)► Intercardinal points (northeast, southeast, Intercardinal points (northeast, southeast,

southwest, northwest)southwest, northwest)► Cardinal-intercardinal points (ie. east northeast = Cardinal-intercardinal points (ie. east northeast =

67.5º and south southeast = 157.5º)67.5º and south southeast = 157.5º)

Cont’Cont’

CourseCourse► Intended direction of travelIntended direction of travel► Expressed in degreesExpressed in degrees► However, influenced by winds, currents, and pilot errorHowever, influenced by winds, currents, and pilot error

HeadingHeading► The direction in which the ship is actually traveling The direction in which the ship is actually traveling

regardless of prescribed courseregardless of prescribed course

BearingBearing► Direction from one point to anotherDirection from one point to another► Expressed as an angle from NorthExpressed as an angle from North► Traditional expressed as relative parts of the vesselTraditional expressed as relative parts of the vessel

Time and Earth’s RotationTime and Earth’s Rotation

► Earth rotates on its axis once in 24hrs = dayEarth rotates on its axis once in 24hrs = day► Each rotation is 360º = 24hrsEach rotation is 360º = 24hrs► Longitude 0º (prime meridian at Greenwich Longitude 0º (prime meridian at Greenwich

England) when sun is directly overhead is England) when sun is directly overhead is 12:00 noon12:00 noon

► Therefore at 180º the time is 12:00am Therefore at 180º the time is 12:00am (midnight)(midnight)

► Therefore, every 15º of longitude E or W of Therefore, every 15º of longitude E or W of Greenwich = 1 hour of time (Zulu or Z. time)Greenwich = 1 hour of time (Zulu or Z. time)

► 360º/24 = 15º360º/24 = 15º

D.R. NavigationD.R. Navigation

► Also known as Dead Reckoning or “Ded” Also known as Dead Reckoning or “Ded” ReckoningReckoning

► Method of navigating using the following Method of navigating using the following from a KNOWN position:from a KNOWN position:

1.1. TimeTime

2.2. SpeedSpeed

3.3. DistanceDistance

4.4. DirectionDirection► Note: Does not account for error or currentsNote: Does not account for error or currents

FormulasFormulas

►Distance = Speed x TimeDistance = Speed x Time

►Speed = Distance / TimeSpeed = Distance / Time

►Time = Distance / SpeedTime = Distance / Speed

Use 60 D = S * T (for minutes)

D

S T