unit 4 navigation instruments

7/29/2019 Unit 4 Navigation Instruments

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UNIT 4 NAVIGATION

NAVIGATION INSTRUMENTS



Navigation instruments are designed

to fix position,

measure direction, distance, the depth of water,

determine speed,

assist in plotting on charts,

observe the weather elements



MAGNETIC COMPASS

The magnetic compass is one

of the oldest instruments used

aboard ships.It is used primarily to determine

the direction.

It was invented in China around

300 A.D.

http://www.wikipedia.org/wiki/China

http://www.wikipedia.org/wiki/China



GYROCOMPASS

A gyrocompass finds North by using a

fast spinning wheel and friction forces to

exploit the rotation of the Earth.

Gyrocompass has two main advantages

over magnetic compass: It finds true

North and It is not affected by metal in aship's hull.



SEXTANT

A sextant measures the angle of declination of a celestial body. One

can calculate the degree of latitude

by knowing the angle and time.



Using sextant



CHARTS

Charts are graphic

representations of areas of the

Earth either in digital or graphicform.

All charts show geographic

features useful to the navigator, as

well as indications of direction.



Data shown on marine charts

include the outline and nature of

coasts, landmarks; currents, winds,tides, lighthouses, buoys, beacons,

position of rocks, bars, reefs,

shoals, wrecks, or other dangers;the nature of bottom (mud, sand,

rock, or gravel) and depth.



On a Mercator chart the meridians

of longitude are represented by

equally spaced vertical lines, andthe parallels of latitude are

represented by horizontal lines that

are closer together near theEquator than near the poles.



In Gnomic projection, lines of latitude and longitude are projected

onto the chart tangent to a single point

on the Earth.

Lines of longitude appear as

straight lines converging towards one

of the poles, while lines of latitude

appear as curves.



Course plotters are used todetermine the direction of a course

or bearing from a given point



Parallel rulers are used for measuring

and plotting directions on charts.



Distance is measured on a chart

with a pair of divider.



Timepieces for keeping

accurate time are a marine

chronometer , a quartz watch or

an atomic clock.



The log is the mariner’s

speedometer for

measuring the speed.



ANSWER THE QUESTIONS

1-What are the purposes of navigation

instruments?



2-What are the superiorities of

gyrocompass over magnetic compass?



3-What is a divider used for?



4-What is used to keep time at sea?



5- What is a sextant used for?



6-What does log measure?



Rewrite sentences by using relative

pronouns.

1- The magnetic compass is one of the

oldest instruments used aboard ships.



2- The modern magnetic compassactually consists of several parallel

magnets mounted to a compass card.



3- All charts show geographic

features useful to the navigator.



4- The most widely used projection innavigation charts is the Mercator named

after Gerardus Mercator.



5-Electromagnetic radiation is energymoving in waves at or near the speed of

light.



What measures the angle of

declination of celestial bodies?

a. chronometer

b.sextant

c. log

d.magnetic compass

e. gyrocompass



What measures the angle of

declination of celestial bodies?

b. sextant



What is used for finding true north?

a. course plotter

b. sextant c. log

d. Mercator chart

e. gyrocompass



What is used for finding true north?

e. gyrocompass



Speed is measured by;

a. log

b. compass c. atomic clock

d. chronometer

e. quartz watch



Speed is measured by;

a. log



What do charts display?

a. navigational aids

b. navigational hazardsc. currents and tides

d. nature of bottom

e. all



What do charts display?

e. all

unit 4 navigation instruments

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