2. Answer the following questions.

1. What does the word “navigate” mean?

2. What are the main methods of navigation at sea?

3. What is Piloting?

4. How does the navigator determine a ship's position in Dead Reckoning?

5. How does the navigator find a ship's position in Electronic and Celestial Navigation?

6. How does the ship leave and enter the port?

7. What are the following instruments used for: compass, chronometer, sextant?

8. What electronic navigation equipment do you know?

9. What units of measurement used at sea do you know?

3. Answer whether the following sentences are true or false. Correct the false ones.

1. To sail a ship requires only great skill.

2. A ship's officers use only modern devices – to tell where their ship is at all times.

3. In dead reckoning the navigator finds a ship's position by observing the sun, moon,

planets, and stars.

4. There are four basic methods of navigation at sea: Dead Reckoning, Electronic Navigation, Compass navigation and Celestial Navigation.

5. Navigation in coastal waters is known as pilotage.

6. A large ship leaves port without any help.

7. A chronometer is used to calculate a ship's latitude by measuring the angle of the sun or of a star above the horizon.

8. At night and in bad weather, a ship's radar can spot icebergs, rocks, and other vessels in time to prevent a collision.

9. Official nautical charts can be only paper.

10. The speed of a vessel is given in knots.

4. Aids to Navigation.

The Instruments of Navigation

One of the basic tools of the marine navigator is the nautical chart. This is a representation, drawn to scale of the water and land areas of a particular region of the Earth's surface. On the chart the navigator keeps a graphic record of the ship's progress. Such a record is kept regardless of the method or combination of methods of navigation that is being used. Lines drawn between successive positions marked on the chart indicate at a glance the courses that the ship has followed. From scales on the chart the navigator can measure directly, without computation, the distance that the ship has travelled. Traditionally, Mercator charts have been used at sea.

2. Piloting

In piloting, the navigator guides a ship largely by the bearings of landmarks. A bearing is the horizontal angle between an object and a reference point.

Bearings are used to determine, or fix, a ship's position. Drawn on a chart, a bearing forms a line of position, a line on which some point must represent the ship's location. Therefore, when two or more bearings intersect (cross-bearings), the intersection must represent the ship's position. In shallow water, soundings help fix a ship's position. Sonic, or echo, depth finders make use of the known speed of sound in water. Sound transmitted from the ship is reflected from the ocean floor to a receiver, which measures elapsed time and calculates distance. Some devices produce fathograms continuous profiles, or graphs, of the ocean bottom.

Marks and lights are the guideposts of the sea, helping the Captain navigate unfamiliar coasts and ports. They consist of lighthouses, buoys and other local structures. At night, the most important ones are lit, and each light has individual characteristics of range, colour, duration, type and number of flashes. Visiting ships pay “light dues” to provide a fund of money for the maintenance of lights, which are looked after by local authorities.

With the aid of charts, the navigator can identify which light he is looking at. A chart may describe a lighthouse as: GpFl(3) 15sec 24M. This cryptic message means that the light gives a group of three flashes, every 15 seconds, and can be seen in clear weather for 24 miles. By day, mariners can still take visual bearings from lighthouses. By the way, there are rarely more than 60m high, because their light could be lost in clouds in poor weather.

Light stations and lightships are maintained along coastlines to warn approaching ships of potential dangers such as off-lying rocks.

Floating navigational aids which are anchored or moored are called buoys. Simple arrangements of colors, shapes, numbers, and lights are employed to indicate the side of a buoy on which a ship should pass when moving in a given direction.

These navigational aids include buoys of two kinds, lateral marks, which mark each side of the channel, and cardinal marks, which relate to compass direction and indicate hazards. Port-side buoys are red, can-shaped and are topped by a flashing red light; starboard buoys are green, cone-shaped, and bear a flashing green light.

Also a navigator may measure with a sextant the altitudes of two or more celestial bodies. He carefully notes to the second the time at which he made his observations. He obtains the time from radio signals or from accurate clocks called chronometers. These are kept set to Greenwich mean time, or GMT, for this is the time the navigator must know as he turns next to the Nautical Almanac.

The Nautical Almanac is a book of astronomical tables from which may be found, for every second of every day, the positions on the celestial sphere of the sun, the stars, the moon, and the planets used in navigation.

The Global Positioning System (GPS) is a highly accurate, worldwide navigation and positioning system that can be used 24 hours a day.

Navigation with the Global Positioning System and a well-designed GPS receiver is very simple. The receiver uses data collected from three or four satellites and presents it in navigation displays.

Course, heading, and track

The terms course, heading, and track are often loosely used. They should, however, be considered to have the meanings that follow. The course is the intended direction of the ship's travel. The heading is the direction in which the ship is pointed at any given time. The track, or course made good, is the direction of a straight line between a point of departure and a present position. The factors that together result in failure to make good an intended course are termed drift. The flow of ocean water, however, is only one of the factors involved.