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Charts and drafting instruments



· Charts are maps of the areas to be navigated with details specific to the marine environment.

· Dividers used for measuring lengths of lines and approximate lengths of non-linear paths on a chart.

· Nautical almanac used to determine the position in the sky of a celestial body after a sight has been taken. A nautical almanac is a publication describing the positions of a selection of celestial bodies for the purpose of enabling navigators to use celestial navigation to determine the position of their ship while at sea.

· Parallel rules used for transferring a line to a parallel position. Also used to compare the orientation of a line to a magnetic or geographic orientation on a compass rose.

Parallel rulers are a drafting instrument used by navigators to draw parallel lines on charts. The tool consists of two straight edges joined by two arms which allow them to move closer or further away while always remaining parallel to each other.

History. The parallel ruler was invented in about 1584 by Fabrizio Mordente, but it was not in common use until the 18th century. In the 19th century, a Captain William Andrew Field (1796 – 1871) improved the design by adding a protractor-style scale to the upper edge of one rule, and compass points to the opposing edge, which made reading bearings easier.

Position finding and celestial navigation instruments

Index mirror: large polished plate that reflects light.

Telescope: optical instrument made of lens that magnifies objects.

Telescope clamp: reinforcing circle.

Eyepiece: lens the user looks through.

Telescope printing: lens adjustment.

Frame: structure that serves as the base for the different parts of the sextant.

Graduated arc: graduated edge of the arc.

Locking device: apparatus that holds the sextant in place.

Drum: graduated button used to take measurements.

Index arm: type of ruler that determines direction or measures an angle.

Screw to regulate small mirror: piece of metal used to adjust the horizon mirror.

Glass filter: colored transparent substance.

Horizon mirror: small polished glass plate that reflects light.

Glass filter: colored transparent substance.

This is an instrument which measures the angle between the celestial body and the horizon. A sextant can also be held horizontally to measure the angle between any two landmarks which allows for calculation of a position on a chart. Navigators’ sextants were primarily used for celestial navigation. The first sextant was made in 1757.

Taking a sight. A navigator would typically go out on the navigation bridge wing. He or she then takes an altitude and notes the exact time. Calculations are then made to determine the ship’s position. This is usually done when the ship is far from land, and lighthouses and other land based objects cannot be used to ascertain our position.

With the advent of the GPS, the marine sextant is slowly becoming obsolete. However, its use and the calculations is a mandatory part of all marine navigational examinations.

Compasses

The compass is an instrument is used for navigation; it generally has a magnetic needle that points towards the Earth’s magnetic North Pole. This is without doubt the most important of all instruments aboard even the most modern vessel, and it is probably the most reliable. The earliest compasses were most likely invented by the Chinese in around 1050 BC. They were created first for the purposes of spiritual life or developing a feng shui environment and then later used for navigation. It was used for maritime navigation by 1117. The use of a compass is recorded in Western Europe between 1187 and 1202 and in Persia in 1232.

There are two widely used and radically different types of compass:

The magnetic compass. The magnetic compass, the most simple and common type of compass, contains a magnet that interacts with the Earth’s magnetic field and aligns itself to point to the magnetic poles. This compass points to the Earth’s magnetic North Pole.

The compass rose. The compass rose is a depiction of orientation and directional that is placed on compasses, maps and charts. Thirty-two points are depicted around a circle in equal intervals, making the four cardinal directions (N, E, S, W), the four intercardinal directions (NE, SE, SW, NW), and the other sixteen secondary intercardinal directions (NE by N, N by E, etc.) Most modern compasses use the 360-degree system of indicating direction on compass. Though the use of degrees, navigation is more accurate than through the use of the compass rose.

Why do we need great compass accuracy at sea? The marine magnetic compass at sea is mainly used for steering a course. The compass reading must be accurate, especially on long sea passages, because a error of one or two degrees in a long course can make a difference of thousands of nautical miles in reaching your destination after many days.

The compass is also used to take bearings of terrestrial and celestial objects for navigation, and errors must be minimized for this purpose. The compass reading at sea must be therefore corrected as accurately as possible.

Compass error is divided into two parts, namely magnetic variation and magnetic deviation.

Compasses are used to determine the direction of true North. However, the compass reading must be corrected for two effects. The first is magnetic declination, the angular difference between magnetic North (the local direction of the Earth’s magnetic field) and true North. The second is magnetic deviation, the angular difference between magnetic North and the compass needle due to nearby sources of iron. Magnetic deviation occurs when a large iron or steel mass warps the magnetic field near the compass. This can be caused by the ship itself or by the cargo if it made up of steel or steel containers.

A gyrocompass is a type of non-magnetic compass which has a needle that spins in relation to the rotation of the Earth to automatically find geographical direction. Gyrocompasses are widely used for navigation on ships, because they have two significant advantages over magnetic compasses:

- they find true north as determined by Earth’s rotation, which is different from, and navigationally more useful than, magnetic north;

- they are unaffected by ferromagnetic materials, such as ship’s steel hull, which change the magnetic field.

IV. Make-up word combinations and translate them:

1) magnetic field 1)____________________________

2) steel needle 2)____________________________

3) magnetic time 3)____________________________

4) geographical north 4)____________________________

5) nautical hull 5)____________________________

6) equal direction 6)____________________________

7) true advantage 7)____________________________

8) compass objects 8)____________________________

9) magnetic navigation 9)____________________________

10) celestial north 10)___________________________

11) exact miles 11)___________________________

12) drafting intervals 12)___________________________

13) celestial reading 11)___________________________

14) significant instrument 12)___________________________

V. Translate the following word combinations into English:

1. сучасний компас – ___________________________________________________

2. прибувати в порт – ___________________________________________________

3. вимірювати кут – ____________________________________________________

4. визначати напрямок – _________________________________________________

5. крило навігаційного містка – ___________________________________________

6. довгий морський перехід – ____________________________________________

7. брати пеленги наземних об’єктів – ______________________________________

______________________________________________________________________

8. малювати паралельні лінії на карті – ____________________________________

______________________________________________________________________

9. визначати місцезнаходження судна – ____________________________________

VI. Read the following text, fill in the blanks with necessary letters, and then translate it:

The plo_ting eq_ipment consists of se_eral instru_ents, the prin_ipal of w_ich are divi_ers, protr_ctors and pa_allel rulers. Divider_ are used b_ navigat_rs for mea_uring dista_ce on the char_. Protr_ctors are inte_ded for meas_ring direc_ion on ch_rts. Par_llel rul_rs con_ists of t_o strai_ht edges, so that if one e_ge is fi_ed along a li_e, the other is restri_ted to m_tion para_lel to the first.

VII. Decide which form of the verb is correct and choose the necessary form of the verb, read and translate the text:

A number of new electronic devices (have been developed; developing) to help the navigator. They (are extending and improving; extend and improve) information about the ship’s position and movement, and (reduce; reducing) the probability of navigation errors. Besides commonly used radar and echo sounder, the modern navigator may (be operated; operate) with highly sophisticated satellite systems for the positioning of the ship at every point of the ocean. Such systems (give; gives) an accuracy of between then one tenth of a mile in all weathers, all over the world. This (have led; has led) to fully automatic navigation in the open sea for modern ships.

VIII. Translate the following sentences into English:

1. Секстант – це навігаційний вимірювальний інструмент.

______________________________________________________________________

2. За допомогою секстанту можна виміряти кут між двома напрямками.

______________________________________________________________________

3. Циркуль використовується для виміряння відстаней на карті.

______________________________________________________________________

4. Компас – це навігаційний прилад, призначений для визначення курсу судна.

______________________________________________________________________

5. Паралельна лінійка – це інструмент для прокладання курсу судна, який складається з двох звичайний лінійок, що з’єднані одна з одною.

______________________________________________________________________

______________________________________________________________________

IX. Self-assessment questions:

1. What is the purpose of navigation?

2. What are navigational instruments?

3. What drafting instruments do you know?

4. What is a nautical almanac?

5. What is a sextant used for?

6. In what navigation is sextant used?

7. What kinds of compasses do you know?

8. What is the construction and application of magnetic compass?

9. What is the compass rose?

10. Why do we need to correct compass errors?

11. What is magnetic declination?

12. What is magnetic deviation?

13. What are the advantages of gyrocompass over magnetic compass?

 

 

UNIT 2





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