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CHAPTER 1
INTRODUCTION TO NAVIGATION
Navigation enables mariners to:
• Locate their position
• Travel from one place to another
Terrestrial Sphere or Globe




A sphere on which is depicted a map
of the Earth (terrestrial globe)
North Pole




                         South Pole
The north and south poles are
located at the ends of the axis on
which Earth rotates.
North Pole



                 Meridians




                               South Pole

Lines running through the poles and
around the Earth are called meridians.
Equator

The great circle of the Earth that is
equidistant from the North Pole and
South Pole

(Cuts every meridian in half)
60°                60°


 30°    Northern Hemisphere     30°




0°
             EQUATOR              0°


 30°                            30°
        Southern Hemisphere

       60°                60°
Northern     Western
Hemisphere    Hemisphere
 North Pole            North Pole




 South Pole            South Pole

 Southern                     Eastern
Hemisphere                 Hemisphere
Hemisphere

Half of a globe
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.
Great Circle

Any circle formed by the intersection
of a plane passing through the Earth’s
center, with the Earth’s surface
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.
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.
What is the significance of the
great circle in navigation?
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.
Arc

Any unbroken part of the
circumference of a circle or
other curved line
Circumference

The distance around a circular area
What is the circumference of the Equator?
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
360°




   1° = 60 minutes
1 minute = 60 seconds
Measurement along a meridian
or parallel is expressed in terms
of degrees, minutes, and seconds
of arc (the curve of the circle).
Greenwich Royal
  Observatory

                       0°


                              0°




The Greenwich meridian is numbered
0, or 0°, and is called the prime
meridian.
Prime Meridian

The meridian running through
Greenwich, England, from which
longitude east and west is measured
INTERNATIONAL DATE LINE




         NORTH
          POLE




    PRIME MERIDIAN
International
Date Line
           New Date
                        Noon
 Old Date




  Old Day                                  0° Prime
                                           Meridian
              New Day
   Midnight                             180°
                                        International
                                        Date Line




              International Date Line
Eastern
Hemisphere
             International
               Date Line
                          Equator




                       Pacific
                       Ocean



                Western Hemisphere
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).
Longitude

Measurement of position east or west
from the prime meridian
Greenwich




                              Prime
                              Meridian

                      W   E




              Longitude
The distance of arc east (E) or west (W)
of the prime meridian, measured along
a parallel
Longitude Lines
Latitude

Measurement of position north or
south of the equator
Latitude




The distance of arc north (N) or
south (S) of the equator, measured
along a meridian
Latitude            Longitude




Equator




                                 Prime
                                meridian
     Grid system of latitude and longitude
     lines
90°                   90°




                       EARTH’S
LATITUDE   LONGITUDE
                         GRID
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°
New Orleans, LA
   30N, 90W
Washington, D.C.

38°58'52"N
latitude

77°01'12"W
longitude

Express latitude
and longitude in
degrees, minutes,
and seconds.
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.
Washington, D.C.

38°58'52"N
latitude

77°01'12"W
longitude

Seconds are used
only if very exact
locations are
required.
Nautical Mile

One minute of arc measured along
the equator, or any other great
circle
6,865 Nautical Miles




    6,888
Nautical Miles




Equatorial Diameter - 6,888 Nautical Miles
Polar Diameter - 6,865 Nautical Miles
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
Dividers




 Distance on a chart is measured along
 the meridian, using a tool called dividers.
Measuring Distance
P
                  30 Nautical
                     Miles
 60°
       Parallel



                    52 Nautical
30°                    Miles
                    60 Nautical
                       Miles
0°
Length of a Degree of Longitude at
        Various Latitudes
Remember!

Distances are not
measured on
parallels of latitude,
because one minute
equals one nautical
mile only along the
equator.

Dividers
1 knot = 1 nautical mile per hour
Origin of the term knot
                          Chip Log




An old sailing day’s log for measuring
the speed of a vessel
True Nautical Direction




Measured from true north (North Pole)
as located on a globe
32-point Compass
Cardinal Points

The four primary directions of the
compass; the north, south, east,
and west points
Cardinal Directions




North, South, East, West:
the four primary directions
of the compass
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.
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.
Express nautical directions in
three digits:
065° (Zero six five degrees)
090° (Zero nine zero degrees)
Heading – Direction the ship is facing
Course – Direction the ship is steered
through the water
MAGNETIC COMPASS     GYROCOMPASS

Magnetic compasses Gyrocompasses
give direction relative reference true
to magnetic north.      north.
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.
MAGNETIC    TRUE
 NORTH     NORTH
Magnetic Compass




A compass having a magnetized
needle generally in line with the
magnetic poles of the Earth
NORTH
                     MAGNETIC
                     POLE




         Canada




     United States
Magnetic compasses point to the
Earth’s northernmost magnetic pole,
located in northern Canada.
Variation Angle

Difference between magnetic and true
north in degrees
How Variation Affects the Compass
   Magnetic North   North Pole
                                 Variation




Remember, variation changes
depending on your position relative
to magnetic north.
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.
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?
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.
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?
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.
Bearing

The direction of an object from an
observer, measured clockwise in one
of three standard ways:

• True bearing
• Magnetic bearing
• Relative bearing
TN




                     Light
                     House


                 090°
                TRUE
               BEARING



True Bearing
True Bearing

Bearing using true north as the
reference
MAGNETIC         TRUE NORTH
      NORTH




                                     Light
                                     House




Difference between true and magnetic bearing
Magnetic Bearing

The direction of an object measured
clockwise from magnetic north
TN




                   RELATIVE
                   BEARING
                     030°


                         Light
                         House



Relative Bearing
Relative Bearing

The direction of an object measured
clockwise from the ship’s head (bow)
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
Objects seen by lookouts are reported
in terms of relative bearing by degrees.
Relative Bearings




•   Dead ahead, or bow – 000°R
•   Starboard beam – 090°R
•   Dead astern – 180°R
•   Port beam – 270°R
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.‖
TN




                                   RELATIVE
                                   BEARING
                                     030°
                                    090°
                                   TRUE   Light
                                  BEARING House


True Bearing = Relative Bearing + True Heading
(Subtract 360° if sum is greater than 360°)
Nautical Chart

Type of map used to navigate on
water
Nautical Chart

A nautical
chart is a
standardized
drawing
representing
part of the
navigable
waters of the
Earth.
Hydrography




Science of measurement, description,
and mapping of the Earth’s surface
waters, with special reference to their
use for navigation
Hydrographic information
given on a chart includes:




• Water depths
• Nature of bottom
• Overhead obstructions
• Navigation aids; buoys,
  lights, and anchorages
Globe             Chart
Impossible to     Necessary to
work navigation   work navigation
problems or       problems
chart courses
Cartographers
Makers of maps and charts who use
math to work out chart projection
techniques
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.
Planar                Conical        Cylindrical
Orthographic        Perspective Conic    Mercator




Chart projections
Chart Projection

Flat surface representative of the
Earth
Mercator Projection
The best-known map or chart projection
Mercator Projection

Earth is projected onto a
cylinder-shaped piece of paper,
wrapped around the globe at the
equator
Geradus Mercator




          Mercator Projection
• Commonly used for navigational charts
• Developed by a Dutch cartographer,
  Geradus Mercator, in the 1500s
• Most useful projection for navigation
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
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
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
Small scales
are used to
depict large
areas on a
chart, and
large scales
are used to
depict small
areas.
Measuring distance on a chart




If an inch on the chart represents 50 miles,
what would five inches represent?
Measuring distance on a chart




If an inch on the chart represents 50 miles,
what would five inches represent?
                250 Miles
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.
Nautical            Sailing




                       Types of Charts
           Harbor
Nautical charts have information for
safe navigation, such as:




• Symbols, figures, and abbreviations
• Depth of water
• Type of bottom
• Navigational aids
Harbor charts are large-scale charts that
show harbors and their approaches in
detail.
Coastal
charts are
intermediate-
scale charts
used to
navigate a
vessel whose
position may
be determined
by landmarks
and lights,
buoys, or
soundings
offshore.
Sounding

The act of measuring the depth of an
area of water
General
ocean sailing
charts are
small-scale
charts
showing the
approaches
to large
areas of the
coast.
INTRODUCTION TO NAVIGATION
       End of Part 1
INTRODUCTION TO NAVIGATION
          Part 2
Depths of
water may
be given in
feet, fathoms,
or meters.
Fathom (of depth)

A unit of length equal to six feet
(1.8 meters); used chiefly in nautical
measurements
Plotting
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.
Parallel Rulers
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
Protractor
An instrument having a graduated arc
for plotting or measuring angles
Three-Arm     Parallel Motion
Protractor   Protractor (PMP)
Measuring
Distance on a
Mercator Chart
Fix (position)

Accurate position determined without
use of any previous position, using
visual, electronic, or celestial
observation
Line of Position
      (LOP)
A line indicating
a series of possible
positions of a ship
as a result of
observation or
measurement
SPIRE




  RANGE          BEARING

       Lines of Position
CAPE



                     DISTANCE ARC



   TANGENT
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.
Visual Range

Two landmarks or navigation aids are
observed in line, one behind the other
Rear
              Marker
              Front
              Marker




Rear Marker            Visual Range
    Front Marker
A circular line of position




       Distance Arc
Radar   Stadimeter


Devices used to
measure distance
to a landmark

                       Sextant
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
Stadimeter
Sextant

An astronomical instrument used to
determine latitude and longitude at
sea by measuring angular distances,
especially the altitudes of Sun, Moon,
and stars
Sextant
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
TOWER



                     1545


  A fix from two
  crossed bearings
DOUBLE POINT
   LIGHT


                      A fix by a
                      bearing and
                      distance from
                      the same object

               1314
SMITH
                           POINT




HALL REEF LIGHT


    A fix from three   JONES
    intersecting       BLUFF

    bearings
LIGHT
                           W


A fix from two
visual ranges
                 LIGHT
                   X




                                 LIGHT
                     2152          W
Visual Fix

Electronic/Celestial Fix

Dead Reckoning Position


Estimated Position


Plotting Symbols
LIGHTHOUSE


                        1300 FIX

1245 FIX




                                   TOWER


                 FACTORY

           Marking Ship’s Fix
Piloting

The determination
of position by
visual means
Piloting




The determination of the course or
position of a ship or airplane by any
of various navigational methods or
devices
Navigation Aids
  Compass

                  Bearing Circle
                                     Fathometer




        Chart


                                       Stadimeter
                                   Radar

                      Buoy
Lighthouse
Echo sounder (Fathometer)

Sonic device used to measure water
depth
Fathometer
Echo Sounder
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)
In piloting, soundings are usually
taken every 5 minutes.
 D=1/2 t x 4,800 feet per second
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.
Electronic navigation is
a form of piloting.
Electronic Navigation

              Advantages

• Unaffected by weather
• Determines ship position electronically

             Disadvantages
      • Equipment malfunction
      • Insufficient coverage
RADAR




RAdio Detection And Ranging
RADAR

Navigation system using reflected
pulses of energy
RADAR
Advantage of radar, as a navigational
aid, is that it does not require external
transmitting stations.
Disadvantage of radar, as a navigational
aid, is that maximum range is currently
limited to slightly more than line-of-sight.
Lighthouse




Use Reliable Radar Targets
Radar System
PIPS




Targets appear on the scope as
bright spots of light called pips.
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.
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.
• Very accurate and rapid
• Used to locate and track storms
• Very important for ship safety
Loran




Long Range Navigation
Loran

Long range navigation system using
radio signals
Loran is a system
of radio signals
broadcast by
stations of known
position.
Loran Receiver

A loran fix is determined by a loran
receiver from the intersection of lines
of position obtained from those shore
stations.
GPS Satellites




           Satellite Navigation
The newest electronic navigation system
is the Global Positioning System (GPS).
Global Positioning
  System (GPS)       • Six 10,900-
                       mile-high
                       orbits
                     • 24 satellites
                     • Continuous
                       three-
                       dimensional
                       fix capability
                     • Fix accurate
                       to within
                       ±10 meters
GPS Navigation
GPS is used for a wide variety of land
navigation purposes, including position
and direction-finding in many new cars
and golf carts.
Military applications of GPS navigation
systems include guidance for:
           • Smart bombs
           • Cruise missiles
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.
Ship’s Inertial Navigation
         System (SINS)




Provides accurate and continuous
dead reckoning (DR) positions
SINS gives ships an accurate and
continuous dead reckoning position
using three gyroscopes to determine
latitude, vertical, and longitude with
great accuracy.
Submarines use SINS to navigate when
submerged for months even when
traveling under the Arctic ice cap.
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
The widespread availability of GPS is
fast making celestial navigation at sea
a vanishing art.
The sextant is used in celestial
navigation to measure the angle
(altitude) between a heavenly body
and the visible horizon.
Sextants
INDEX MIRROR
                                          LENS
HORIZON
                          INDEX ARM       HOOD
MIRROR
                           TELESCOPE




                                         VERNIER
 ARC                                      SCALE
SCALE
                                 MICROMETER
 DRUM SCALE                         SCREW

          Sextant — Nomenclature
          Reading the Vernier Scale
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
Visual Fix

Electronic/Celestial Fix

Dead Reckoning Position


Estimated Position


Plotting Symbols
FIX
       DR POSITION
                         DESTINATION




1200
          DEAD RECKONING TRACK
Set and Drift

Set – The direction in which a ship
      is forced by wind and current


Drift – The speed of that force in
        knots
FIX
       DR POSITION
                                DESTINATION




                                          1615

                                   1600



1200
             Effect of Set and Drift
A fix at 1200 is plotted and labeled.
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.
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.
The spot is labeled ―1300DR.‖
The Captain orders the Officer
of the Deck (OOD) to put ship on
a new course, 117° at 1330.
Using dividers, mark a spot 7½
miles from the 1300 DR position
along the direction the ship is
steaming.
Label position 1330DR, and
draw a new course line in the
direction of 117°.
Plotting a ship’s
           DR track from one
           fix to the next is a
1400 FIX   continuous
           process while
           underway.
DR PLOT
1400 FIX
At sea, the navigator will use celestial or
electronic means to get positive fixes at
least every morning, noon, and evening.
In piloting waters, the navigator will
normally be on the bridge getting exact
fixes whenever usable navigation aids
come into sight.
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.
Q.1. Define navigation.
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
Q.2. What is a chart?
Q.2. What is a chart?


A.2. A type of map used to navigate
     on water
Q.3. What are the imaginary lines
     that run through the poles and
     around the Earth?
Q.3. What are the imaginary lines
     that run through the poles and
     around the Earth?


A.3. Meridians or lines of longitude
Q.4. What divides the Earth into the
     northern and southern
     hemispheres?
Q.4. What divides the Earth into the
     northern and southern
     hemispheres?


A.4. The Equator
Q.5. What is a Great Circle?
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
Q.6. Are all meridians great circles?
Q.6. Are all meridians great circles?


A.6. Yes
Q.7. What is the name given to the
     meridian on which the Royal
     Observatory at Greenwich,
     England, is located?
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
Q.8. Do parallel and latitudinal lines
     run in the same direction?
Q.8. Do parallel and latitudinal lines
     run in the same direction?


A.8. Yes
Q.9. Navigators determine their
     ship's position using what
     coordinate system?
Q.9. Navigators determine their
     ship's position using what
     coordinate system?


A.9. Latitude and Longitude
Q.10. If the latitude of the equator is
      0 degrees, what is the latitude
      of the North Pole?
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
Q.11. Latitude and longitude are
      expressed in what units?
Q.11. Latitude and longitude are
      expressed in what units?


A.11. Degrees, minutes, and
      seconds
Q.12. How many degrees are there in
      a circle?
Q.12. How many degrees are there in
      a circle?


A.12. 360
Q.13. Approximately how many
      yards are in a nautical mile?
Q.13. Approximately how many
      yards are in a nautical mile?


A.13. 2000 yds.
Q.14. What are meridians?
Q.14. What are meridians?


A.14. Great Circles which pass
      through the Earth’s poles
Q.15. In navigation what is a ―knot?‖
Q.15. In navigation what is a ―knot?‖


A.15. A seagoing term meaning one
      nautical mile per hour
Q.16. How is direction expressed?
Q.16. How is direction expressed?


A.16. As an angle between 000
      degrees and 359 degrees
Q.17. What are the cardinal points?
Q.17. What are the cardinal points?


A.17. North, East, South, and West
Q.18. Define ―true bearing.‖
Q.18. Define ―true bearing.‖


A.18. The direction of an object
      measured clockwise from true
      north
Q.19. What does chart projection
      entail?
Q.19. What does chart projection
      entail?


A.19. Projecting a three-dimensional
      object on a two-dimensional
      plane
Q.20. What is the best-known map or
      chart projection called?
Q.20. What is the best-known map or
      chart projection called?


A.20. Mercator projection
Q.21. What are the three basic types
      of charts used by the Navy?
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
Q.22. What is a cartographer?
Q.22. What is a cartographer?


A.22. One who makes maps and
      charts
Q.23. What is a fix?
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.
Q.24. What is the difference between
      directions measured on a
      gyrocompass and those
      measured on a magnetic
      compass?
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.
Q.25. How is distance on a Mercator
      chart measured?
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
Q.26. If a half-inch on a chart
      represents 10 miles, how many
      inches would represent 100
      miles?
Q.26. If a half-inch on a chart
      represents 10 miles, how many
      inches would represent 100
      miles?


A.26. Five inches
Q.27. What is the shortest distance
      between two points on a
      globe?
Q.27. What is the shortest distance
      between two points on a
      globe?


A.27. An arc of a great circle
Q.28. How many feet are in one
      fathom?
Q.28. How many feet are in one
      fathom?


A.28. Six feet
Q.29. What is a line of position
      (LOP)?
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
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?
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)
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?
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
Sphere

A round body whose surface is at all
points equidistant from the center
Meridian

A great circle of the Earth passing
through the poles and any given
point on the Earth's surface
Parallel

Lines of latitude with only the equator
being a great circle
Dividers

A two–pointed compass used for
dividing lines and measuring
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
Magnetic Compass

Directional instrument that points to
the north magnetic pole


          Gyrocompass

Aligned with true north by means of a
spinning gyroscope
Distortion

The state of being misrepresented
a false
Development
of a Mercator
Projection
Sounding
LORAN CHART
Global Positioning System (GPS)

 Electronic navigation system using
 satellites

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Intro to Navigation

  • 2. Navigation enables mariners to: • Locate their position • Travel from one place to another
  • 3. Terrestrial Sphere or Globe A sphere on which is depicted a map of the Earth (terrestrial globe)
  • 4. North Pole South Pole The north and south poles are located at the ends of the axis on which Earth rotates.
  • 5. North Pole Meridians South Pole Lines running through the poles and around the Earth are called meridians.
  • 6. Equator The great circle of the Earth that is equidistant from the North Pole and South Pole (Cuts every meridian in half)
  • 7. 60° 60° 30° Northern Hemisphere 30° 0° EQUATOR 0° 30° 30° Southern Hemisphere 60° 60°
  • 8. Northern Western Hemisphere Hemisphere North Pole North Pole South Pole South Pole Southern Eastern Hemisphere Hemisphere
  • 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. Great Circle Any circle formed by the intersection of a plane passing through the Earth’s center, with the Earth’s surface
  • 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. 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. What is the significance of the great circle in navigation?
  • 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. Arc Any unbroken part of the circumference of a circle or other curved line
  • 18. What is the circumference of the Equator?
  • 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. 360° 1° = 60 minutes 1 minute = 60 seconds
  • 21. Measurement along a meridian or parallel is expressed in terms of degrees, minutes, and seconds of arc (the curve of the circle).
  • 22. Greenwich Royal Observatory 0° 0° The Greenwich meridian is numbered 0, or 0°, and is called the prime meridian.
  • 23. Prime Meridian The meridian running through Greenwich, England, from which longitude east and west is measured
  • 24. INTERNATIONAL DATE LINE NORTH POLE PRIME MERIDIAN
  • 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. Eastern Hemisphere International Date Line Equator Pacific Ocean Western Hemisphere
  • 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. Longitude Measurement of position east or west from the prime meridian
  • 29. Greenwich Prime Meridian W E Longitude The distance of arc east (E) or west (W) of the prime meridian, measured along a parallel
  • 31. Latitude Measurement of position north or south of the equator
  • 32. Latitude The distance of arc north (N) or south (S) of the equator, measured along a meridian
  • 33. Latitude Longitude Equator Prime meridian Grid system of latitude and longitude lines
  • 34. 90° 90° EARTH’S LATITUDE LONGITUDE GRID
  • 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. New Orleans, LA 30N, 90W
  • 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. Washington, D.C. 38°58'52"N latitude 77°01'12"W longitude Seconds are used only if very exact locations are required.
  • 40. Nautical Mile One minute of arc measured along the equator, or any other great circle
  • 41. 6,865 Nautical Miles 6,888 Nautical Miles Equatorial Diameter - 6,888 Nautical Miles Polar Diameter - 6,865 Nautical Miles
  • 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. Dividers Distance on a chart is measured along the meridian, using a tool called dividers.
  • 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. Remember! Distances are not measured on parallels of latitude, because one minute equals one nautical mile only along the equator. Dividers
  • 47. 1 knot = 1 nautical mile per hour
  • 48. Origin of the term knot Chip Log An old sailing day’s log for measuring the speed of a vessel
  • 49. True Nautical Direction Measured from true north (North Pole) as located on a globe
  • 51. Cardinal Points The four primary directions of the compass; the north, south, east, and west points
  • 52. Cardinal Directions North, South, East, West: the four primary directions of the compass
  • 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. 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. Express nautical directions in three digits: 065° (Zero six five degrees) 090° (Zero nine zero degrees)
  • 56. Heading – Direction the ship is facing Course – Direction the ship is steered through the water
  • 57. MAGNETIC COMPASS GYROCOMPASS Magnetic compasses Gyrocompasses give direction relative reference true to magnetic north. north.
  • 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. MAGNETIC TRUE NORTH NORTH
  • 60. Magnetic Compass A compass having a magnetized needle generally in line with the magnetic poles of the Earth
  • 61. NORTH MAGNETIC POLE Canada United States Magnetic compasses point to the Earth’s northernmost magnetic pole, located in northern Canada.
  • 62. Variation Angle Difference between magnetic and true north in degrees
  • 63. How Variation Affects the Compass Magnetic North North Pole Variation Remember, variation changes depending on your position relative to magnetic north.
  • 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. 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. 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. 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. 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. Bearing The direction of an object from an observer, measured clockwise in one of three standard ways: • True bearing • Magnetic bearing • Relative bearing
  • 70. TN Light House 090° TRUE BEARING True Bearing
  • 71. True Bearing Bearing using true north as the reference
  • 72. MAGNETIC TRUE NORTH NORTH Light House Difference between true and magnetic bearing
  • 73. Magnetic Bearing The direction of an object measured clockwise from magnetic north
  • 74. TN RELATIVE BEARING 030° Light House Relative Bearing
  • 75. Relative Bearing The direction of an object measured clockwise from the ship’s head (bow)
  • 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. Objects seen by lookouts are reported in terms of relative bearing by degrees.
  • 78. Relative Bearings • Dead ahead, or bow – 000°R • Starboard beam – 090°R • Dead astern – 180°R • Port beam – 270°R
  • 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. TN RELATIVE BEARING 030° 090° TRUE Light BEARING House True Bearing = Relative Bearing + True Heading (Subtract 360° if sum is greater than 360°)
  • 81. Nautical Chart Type of map used to navigate on water
  • 82. Nautical Chart A nautical chart is a standardized drawing representing part of the navigable waters of the Earth.
  • 83. Hydrography Science of measurement, description, and mapping of the Earth’s surface waters, with special reference to their use for navigation
  • 84. Hydrographic information given on a chart includes: • Water depths • Nature of bottom • Overhead obstructions • Navigation aids; buoys, lights, and anchorages
  • 85. Globe Chart Impossible to Necessary to work navigation work navigation problems or problems chart courses
  • 86. Cartographers Makers of maps and charts who use math to work out chart projection techniques
  • 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. Planar Conical Cylindrical Orthographic Perspective Conic Mercator Chart projections
  • 89. Chart Projection Flat surface representative of the Earth
  • 90. Mercator Projection The best-known map or chart projection
  • 91. Mercator Projection Earth is projected onto a cylinder-shaped piece of paper, wrapped around the globe at the equator
  • 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. 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. 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. 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. Small scales are used to depict large areas on a chart, and large scales are used to depict small areas.
  • 97. Measuring distance on a chart If an inch on the chart represents 50 miles, what would five inches represent?
  • 98. Measuring distance on a chart If an inch on the chart represents 50 miles, what would five inches represent? 250 Miles
  • 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. Nautical Sailing Types of Charts Harbor
  • 101. Nautical charts have information for safe navigation, such as: • Symbols, figures, and abbreviations • Depth of water • Type of bottom • Navigational aids
  • 102. Harbor charts are large-scale charts that show harbors and their approaches in detail.
  • 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. Sounding The act of measuring the depth of an area of water
  • 105. General ocean sailing charts are small-scale charts showing the approaches to large areas of the coast.
  • 106. INTRODUCTION TO NAVIGATION End of Part 1
  • 108. Depths of water may be given in feet, fathoms, or meters.
  • 109. Fathom (of depth) A unit of length equal to six feet (1.8 meters); used chiefly in nautical measurements
  • 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.
  • 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. Protractor An instrument having a graduated arc for plotting or measuring angles
  • 115. Three-Arm Parallel Motion Protractor Protractor (PMP)
  • 117. Fix (position) Accurate position determined without use of any previous position, using visual, electronic, or celestial observation
  • 118. Line of Position (LOP) A line indicating a series of possible positions of a ship as a result of observation or measurement
  • 119. SPIRE RANGE BEARING Lines of Position CAPE DISTANCE ARC TANGENT
  • 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. Visual Range Two landmarks or navigation aids are observed in line, one behind the other
  • 122. Rear Marker Front Marker Rear Marker Visual Range Front Marker
  • 123. A circular line of position Distance Arc
  • 124. Radar Stadimeter Devices used to measure distance to a landmark Sextant
  • 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
  • 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
  • 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. TOWER 1545 A fix from two crossed bearings
  • 131. DOUBLE POINT LIGHT A fix by a bearing and distance from the same object 1314
  • 132. SMITH POINT HALL REEF LIGHT A fix from three JONES intersecting BLUFF bearings
  • 133. LIGHT W A fix from two visual ranges LIGHT X LIGHT 2152 W
  • 134. Visual Fix Electronic/Celestial Fix Dead Reckoning Position Estimated Position Plotting Symbols
  • 135. LIGHTHOUSE 1300 FIX 1245 FIX TOWER FACTORY Marking Ship’s Fix
  • 137. Piloting The determination of the course or position of a ship or airplane by any of various navigational methods or devices
  • 138. Navigation Aids Compass Bearing Circle Fathometer Chart Stadimeter Radar Buoy Lighthouse
  • 139. Echo sounder (Fathometer) Sonic device used to measure water depth
  • 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. In piloting, soundings are usually taken every 5 minutes. D=1/2 t x 4,800 feet per second
  • 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. Electronic navigation is a form of piloting.
  • 146. Electronic Navigation Advantages • Unaffected by weather • Determines ship position electronically Disadvantages • Equipment malfunction • Insufficient coverage
  • 148. RADAR Navigation system using reflected pulses of energy
  • 149. RADAR
  • 150. Advantage of radar, as a navigational aid, is that it does not require external transmitting stations.
  • 151. Disadvantage of radar, as a navigational aid, is that maximum range is currently limited to slightly more than line-of-sight.
  • 154. PIPS Targets appear on the scope as bright spots of light called pips.
  • 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. 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. • Very accurate and rapid • Used to locate and track storms • Very important for ship safety
  • 159. Loran Long range navigation system using radio signals
  • 160. Loran is a system of radio signals broadcast by stations of known position.
  • 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. GPS Satellites Satellite Navigation The newest electronic navigation system is the Global Positioning System (GPS).
  • 163. Global Positioning System (GPS) • Six 10,900- mile-high orbits • 24 satellites • Continuous three- dimensional fix capability • Fix accurate to within ±10 meters
  • 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. Military applications of GPS navigation systems include guidance for: • Smart bombs • Cruise missiles
  • 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. Ship’s Inertial Navigation System (SINS) Provides accurate and continuous dead reckoning (DR) positions
  • 169. SINS gives ships an accurate and continuous dead reckoning position using three gyroscopes to determine latitude, vertical, and longitude with great accuracy.
  • 170. Submarines use SINS to navigate when submerged for months even when traveling under the Arctic ice cap.
  • 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. The widespread availability of GPS is fast making celestial navigation at sea a vanishing art.
  • 173. The sextant is used in celestial navigation to measure the angle (altitude) between a heavenly body and the visible horizon.
  • 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. 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. Visual Fix Electronic/Celestial Fix Dead Reckoning Position Estimated Position Plotting Symbols
  • 178. FIX DR POSITION DESTINATION 1200 DEAD RECKONING TRACK
  • 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. FIX DR POSITION DESTINATION 1615 1600 1200 Effect of Set and Drift
  • 181. A fix at 1200 is plotted and labeled.
  • 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.
  • 184. 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.
  • 185.
  • 186. The spot is labeled ―1300DR.‖
  • 187. The Captain orders the Officer of the Deck (OOD) to put ship on a new course, 117° at 1330.
  • 188. Using dividers, mark a spot 7½ miles from the 1300 DR position along the direction the ship is steaming.
  • 189.
  • 190. Label position 1330DR, and draw a new course line in the direction of 117°.
  • 191.
  • 192. Plotting a ship’s DR track from one fix to the next is a 1400 FIX continuous process while underway.
  • 194. At sea, the navigator will use celestial or electronic means to get positive fixes at least every morning, noon, and evening.
  • 195. In piloting waters, the navigator will normally be on the bridge getting exact fixes whenever usable navigation aids come into sight.
  • 196. 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.
  • 198. 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
  • 199. Q.2. What is a chart?
  • 200. Q.2. What is a chart? A.2. A type of map used to navigate on water
  • 201. Q.3. What are the imaginary lines that run through the poles and around the Earth?
  • 202. Q.3. What are the imaginary lines that run through the poles and around the Earth? A.3. Meridians or lines of longitude
  • 203. Q.4. What divides the Earth into the northern and southern hemispheres?
  • 204. Q.4. What divides the Earth into the northern and southern hemispheres? A.4. The Equator
  • 205. Q.5. What is a Great Circle?
  • 206. 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
  • 207. Q.6. Are all meridians great circles?
  • 208. Q.6. Are all meridians great circles? A.6. Yes
  • 209. Q.7. What is the name given to the meridian on which the Royal Observatory at Greenwich, England, is located?
  • 210. 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
  • 211. Q.8. Do parallel and latitudinal lines run in the same direction?
  • 212. Q.8. Do parallel and latitudinal lines run in the same direction? A.8. Yes
  • 213. Q.9. Navigators determine their ship's position using what coordinate system?
  • 214. Q.9. Navigators determine their ship's position using what coordinate system? A.9. Latitude and Longitude
  • 215. Q.10. If the latitude of the equator is 0 degrees, what is the latitude of the North Pole?
  • 216. 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
  • 217. Q.11. Latitude and longitude are expressed in what units?
  • 218. Q.11. Latitude and longitude are expressed in what units? A.11. Degrees, minutes, and seconds
  • 219. Q.12. How many degrees are there in a circle?
  • 220. Q.12. How many degrees are there in a circle? A.12. 360
  • 221. Q.13. Approximately how many yards are in a nautical mile?
  • 222. Q.13. Approximately how many yards are in a nautical mile? A.13. 2000 yds.
  • 223. Q.14. What are meridians?
  • 224. Q.14. What are meridians? A.14. Great Circles which pass through the Earth’s poles
  • 225. Q.15. In navigation what is a ―knot?‖
  • 226. Q.15. In navigation what is a ―knot?‖ A.15. A seagoing term meaning one nautical mile per hour
  • 227. Q.16. How is direction expressed?
  • 228. Q.16. How is direction expressed? A.16. As an angle between 000 degrees and 359 degrees
  • 229. Q.17. What are the cardinal points?
  • 230. Q.17. What are the cardinal points? A.17. North, East, South, and West
  • 231. Q.18. Define ―true bearing.‖
  • 232. Q.18. Define ―true bearing.‖ A.18. The direction of an object measured clockwise from true north
  • 233. Q.19. What does chart projection entail?
  • 234. Q.19. What does chart projection entail? A.19. Projecting a three-dimensional object on a two-dimensional plane
  • 235. Q.20. What is the best-known map or chart projection called?
  • 236. Q.20. What is the best-known map or chart projection called? A.20. Mercator projection
  • 237. Q.21. What are the three basic types of charts used by the Navy?
  • 238. 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
  • 239. Q.22. What is a cartographer?
  • 240. Q.22. What is a cartographer? A.22. One who makes maps and charts
  • 241. Q.23. What is a fix?
  • 242. 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.
  • 243. Q.24. What is the difference between directions measured on a gyrocompass and those measured on a magnetic compass?
  • 244. 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.
  • 245. Q.25. How is distance on a Mercator chart measured?
  • 246. 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
  • 247. Q.26. If a half-inch on a chart represents 10 miles, how many inches would represent 100 miles?
  • 248. Q.26. If a half-inch on a chart represents 10 miles, how many inches would represent 100 miles? A.26. Five inches
  • 249. Q.27. What is the shortest distance between two points on a globe?
  • 250. Q.27. What is the shortest distance between two points on a globe? A.27. An arc of a great circle
  • 251. Q.28. How many feet are in one fathom?
  • 252. Q.28. How many feet are in one fathom? A.28. Six feet
  • 253. Q.29. What is a line of position (LOP)?
  • 254. 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
  • 255. 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?
  • 256. 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)
  • 257. 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?
  • 258. 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
  • 259. Sphere A round body whose surface is at all points equidistant from the center
  • 260. Meridian A great circle of the Earth passing through the poles and any given point on the Earth's surface
  • 261. Parallel Lines of latitude with only the equator being a great circle
  • 262. Dividers A two–pointed compass used for dividing lines and measuring
  • 263. 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
  • 264. Magnetic Compass Directional instrument that points to the north magnetic pole Gyrocompass Aligned with true north by means of a spinning gyroscope
  • 265. Distortion The state of being misrepresented a false
  • 269. Global Positioning System (GPS) Electronic navigation system using satellites