Marine Charts and
Navigation
Oceanography
2014
Earth Coordinate System
►
1.
2.
3.
4.
Latitude
Parallels of arc
0º-90º N-S from the
equator to poles
1º = 60’ (1’=60 sec)
small circles
►
1.
2.
3.
4.
Longitude
Meridians of angle
0º (prime meridian) 180º E-W pole to
pole
Prime meridian is
measured at
Greenwich England
great circles
Marine Charts
Water depths
► Configuration of the shoreline in coastal
waters
► Navigational lights, buoys, landmarks
► Chart title block
► Nature of the bottom (hrd, rky, g, sh, s,
co)
► North is the top, latitude scale on side,
and longitude on top and bottom
► Many charts cover less than a 1º of lat
or long, so be careful when “fixing” a
position
►
Units of Distance
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Statute vs. nautical miles
1 nautical mile = 1’ of latitude
1 nautical mile = 1.15 statute miles
1º of latitude = 60’ = 60 nautical miles
1º = 60 nautical miles = 69 statute miles
Use a drafting compass or dividers and spread points to
apply to chart bar scale to determine distance
Units of Speed
► Knot
= 1 nautical
mile/hour
►1
knot x 1.85 = km/hr
Plotting a Course
Magnetic vs. true (geographic) North
► Use the “Compass rose” on the chart
► The compass is graduated from 0º-360º and broken into
32 points on the compass
► Cardinal points (0, 90, 180, 270 degrees)
► Intercardinal points (northeast, southeast, southwest,
northwest)
► Cardinal-intercardinal points (ie. east northeast = 67.5º
and south southeast = 157.5º)
►
Cont’
Course
►
Intended direction of travel
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Expressed in degrees
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However, influenced by winds, currents, and pilot error
Heading
►
The direction in which the ship is actually traveling regardless of
prescribed course
Bearing
►
Direction from one point to another
►
Expressed as an angle from North
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Traditional expressed as relative parts of the vessel
Time and Earth’s Rotation
► Earth
rotates on its axis once in 24hrs = day
► Each rotation is 360º = 24hrs
► Longitude 0º (prime meridian at Greenwich
England) when sun is directly overhead is 12:00
noon
► Therefore at 180º the time is 12:00am (midnight)
► Therefore, every 15º of longitude E or W of
Greenwich = 1 hour of time (Zulu or Z. time)
► 360º/24 = 15º
D.R. Navigation
Also known as Dead Reckoning or “Ded”
Reckoning
► Method of navigating using the following from a
KNOWN position:
1. Time
2. Speed
3. Distance
4. Direction
► Note: Does not account for error or currents
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Formulas
► Distance
► Speed
► Time
= Speed x Time
D
= Distance / Time
= Distance / Speed
Use 60 D = S * T (for minutes)
S
T