Navigation

navigation, science and technology of finding the position and directing the course of vessels and aircraft.

Early Navigational Techniques

In ancient times, mariners navigated by the guidance of the sun and stars and landmarks along the coast. The Phoenicians were probably the most daring of the ancient navigators. They built large ships and, traveling out of sight of land by day and by night, probably circumnavigated Africa. The Polynesians navigated from island to island with the help of guide stars, knowledge of which was passed from generation to generation.

In England, Queen Elizabeth I did much to establish navigation laws, giving additional powers to Trinity House, a guild that had been created in 1514 for the piloting of ships and the regulation of British navigation. During this period the study of bodies of water, or hydrography, was given much attention, and harbors and the outlets of rivers were surveyed and buoyed. A tremendous advance in navigation had taken place with the introduction of the compass. Early in the 15th cent. there was progress by the Portuguese under the leadership of Prince Henry the Navigator, who built an observatory and formulated tables of the declinations of the sun; collected a great amount of nautical information, which he placed in practical form; made charts; and sponsored expeditions that led to numerous discoveries.

Introduction of Navigational Instruments

With the development of shipbuilding and the increase in knowledge of astronomy, there was increased use of instruments. The cross-staff was used to find latitude early in the 15th cent. It consisted of two pieces of wood, the cross at right angles to, and sliding on, the staff. At each end of the 26-in. (66-cm) cross a small hole was bored, and at the end of the staff a sight was fixed. To measure the altitude of a heavenly body, the instrument was sighted in that direction, and the cross was moved forward or back until the heavenly body appeared through the upper hole and the horizon through the lower. The altitude could then be read on a scale marked on the staff. Another device used for finding latitude was the astrolabe. Both were far from accurate.

The navigating equipment carried by Columbus probably was simply a compass, a cross-staff, and a table of the sun's declination. Vasco da Gama on his first voyage around the Cape of Good Hope in 1497 used an astrolabe. The Flemish geographer G. K. Mercator's work in improving charts at the end of the 16th cent., the works of the Spanish scientist Martín Cortés during the same period, the determining of the earth's circumference, and the introduction of logarithms at the beginning of the 17th cent. by the Scottish mathematician John Napier all helped advance navigation.

By the middle of the 18th cent. a quadrant could be used to find latitude and a log line and half-minute glass could help keep track of distance traveled; but the problem of finding the longitude remained unsolved until the invention of the chronometer. The appearance of the Nautical Almanac (see ephemeris) in 1767 was a great step forward in navigation, and the 19th cent. saw the development of books on navigation that far surpassed any earlier instructions, such as the standard book by Nathaniel Bowditch, an American mathematician. The system of dead reckoning, which was much refined, is the art of finding a position by calculating the point of departure (i.e., the last known point of latitude and longitude), the course (as shown by the compass), the speed and the distance traveled according to the log, and the time elapsed. The use of buoys and the making of careful charts made navigation easier, while the fixing of positions by sextant and astronomical charts was greatly improved.

Modern Navigational Tools

The next great revolution in navigation occurred in the 20th cent., when radio signals came into wide use. The development of radar, loran, and radio direction finding during World War II caused fundamental changes in navigational practice; a mariner or pilot today can turn on a Loran or Global Positioning System receiver and determine position and course to within a few yards. Inertial guidance systems, most often used to navigate submarines, aircraft, and spacecraft, allow navigation without contact with a ground base. In such systems, a computer navigates the vehicle with the aid of an inertial navigator device, which consists of a gyroscope to indicate direction and an accelerometer to measure changes in speed and direction. Inertial guidance systems and terrain-following radar allow a cruise missile to fly a thousand miles and hit its designated target.

See also air navigation; navigation satellite.

Bibliography

See latest edition of Bowditch's Practical Navigator; see also D. Sobel, Longitude (1995).

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navigation

Science of directing a craft by determining its position, course, and distance traveled. Early mariners followed landmarks visible on shore and studied prevailing winds for clues to direction. The Phoenicians and Polynesians sailed out of sight of land and used the stars to set their course. The compass (first used by the Chinese c. 1100) was the first navigational aid that gave a constant reference point, though its accuracy was limited, especially in heavy seas. Modern compasses are stabilized by gyroscopes and housed in binnacles that compensate for the craft's motion. Ship speed was first calculated by dropping overboard a log attached to a reel of line knotted at regular intervals; the number of knots exposed while the log drifted and a sandglass emptied gave the vessel's speed in knots (nautical mph). Charts are another essential navigational tool. Fixing a position requires charts detailing known locations, together with instruments that calculate a vessel's bearing relative to them. The earliest instrument for determining latitude was the quadrant, which measured the altitude of the polestar or the noonday sun. Other early instruments included the sextant and the astrolabe. Longitude (used for navigation with increasing success in the 17th–18th century) was fixed using chronometers and tables showing positions of celestial bodies throughout the year. In the 20th century, radio beacons and satellite networks allowed aircraft and ships to determine their position. Dead reckoning uses an accurate history of a vessel's headings and speeds drawn from gyroscopes and from computerized measurements of the craft's acceleration. See also Global Positioning System.

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navigation [‚nav·ə′gā·shən]

(computer science)

In a database management system, the techniques provided for locating information within the system.

(engineering)

The process of directing the movement of a craft so that it will reach its intended destination; subprocesses are position fixing, dead reckoning, pilotage, and homing.

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Navigation 

(1) Ship handling, shipping.

(2) The time of year when navigation is possible in terms of local climatic conditions.

(3) The main branch of ship handling, in which the theoretical grounds and practical procedures of ship operation are developed.

The origin of maritime navigation dates to remote antiquity. The simplest procedures of navigation were known not only to the ancient Egyptians and Phoenicians but also to peoples who were at a lower stage of development. The principles of modern navigation were established by use of a magnetic pointer to determine the ship’s course (11th century), the compilation of charts in a direct orthogonal cylindrical projection (G. Mercator, 1569), and the invention of the deck log (19th century). At the turn of the 20th century, advances in physics were the basis for the development of electrical and electronic navigation instruments. In Russia the first training aid for navigation was compiled in 1703 by L. F. Magnitskii, an instructor at the School of Mathematical and Navigational Sciences, which was founded by Peter I in 1701. Russian seamen and scholars such as S. I. Mordvinov, L. Euler, and M. V. Lomonosov made a major contribution to work on navigational problems. Round-the-world voyages and scientific expeditions conducted by Russian seamen contributed to the further development of navigational science. Textbooks were written in which the methods of navigation were given a treatment close to that of the present day. P. Ia. Gamaleia’s textbook Theory and Practice of Navigation, which was published in several editions and served as a main guide to navigation in the first half of the 19th century, first came out in 1806. A new stage in the development of navigation was opened by the invention of radio by A. S. Popov. Major contributions to the establishment and development of the Soviet school of navigation were made by such scientists as N. N. Matusevich, N. A. Sakellari, A. P. Iushchenko, and K. S. Ukhov.

The tasks of modern navigation are the selection of the safest and most convenient route for a ship, the use of navigational instruments and devices to determine the direction of travel and the distance covered by a ship at sea (including determination of corrections for the readings of such instruments), the study and selection of the cartographic projections that are most convenient for navigation and their use to solve problems of navigation by analytical and graphic methods, the consideration of the effect of external factors that cause deviation of the ship from the selected route, the determination of the ship’s location on the basis of land reference points and navigation satellites, and the assessment of the accuracy of such determinations. A number of problems of navigation are solved using methods of geodesy, cartography, hydrography, oceanography, and meteorology.

A ship’s voyage between specific points requires the calculation and plotting of its route on maritime navigation charts, and also determination of a course that will ensure that the ship travels along the planned route with consideration for the effect of external disturbances (wind and currents). The nautical mile has been adopted as the fundamental unit for measuring distance at sea, and the degree as the fundamental unit for measuring direction.

The shortest distance between two given points on the surface of the earth, which is assumed to be spherical, is the shorter arc of the great circle that passes through the points. Except in cases when a ship travels along a meridian or the equator, the great circle intersects the meridians at various angles. Therefore, a ship traveling along such a curve must change course continuously. In practice it is more convenient to travel a course that is a constant angle to the meridians and that can be represented in a Mercator projection on a chart by a straight line—a rhumb line. At great distances, however, the difference between the length of the great circle and that of the rhumb line becomes significant. Therefore, in such cases the great circle is computed and intermediate points are plotted, between which the ship sails along the rhumb line.

The graphic representation of a ship’s route on a chart is called a plot. During the voyage the navigator keeps a continuous record of the ship’s position, according to its direction and the distance traveled, on the basis of readings of the ship’s compass and log and data on the current and drift. The method of computing a ship’s position on the basis of the elements of its motion is called deal reckoning, and the ship’s position on a chart as obtained by this method is called the dead-reckoning position of the ship. However, no matter how carefully the dead reckoning is performed, the position thus determined always deviates from the actual position of the ship because of errors in the corrections of compass readings and the log, inaccuracies in incorporating the elements of the current and drift, and deviations of the ship from course caused by various factors. Therefore, to eliminate errors, the dead reckoning is continuously corrected during a voyage by means of periodic determinations of the ship’s position (observations) according to land reference points (that is, by navigational methods) or according to heavenly bodies by using methods of nautical astronomy. The navigational methods are based on measurement of the distance and direction (or combinations thereof) to objects whose coordinates are known, or of the angles between the objects. Each measurement gives one position line. The intersection of two position lines determines the ship’s observed position. With three or more lines it is possible not only to determine the ship’s position but also to find the probable values of the errors of observation. Reference points for navigational determinations near the coast include natural landmarks or artificial structures (mainly navigational aids, such as lighthouses, signs, and channel markers), which are entered on the chart and can be observed visually or by radar or the signals of circular or course radio beacons; sound signals; and deeps. Pulsed, pulsed-phase, and phase radio navigation systems or quadrant radio beacons are used at great distances from shore.

The increase in the traffic density on sea routes and in the dimensions and speeds of oceangoing ships requires improvements in equipment and methods of navigation. Use of the Doppler effect in sonar logs, which makes it possible to measure the speed of a ship with respect to the bottom, is one way of increasing the accuracy of dead reckoning. During approaches to ports and when sailing in crowded channels, the required accuracy of guidance is ensured by the use of precision short-range radio navigation systems or coastal radar stations. Global radio navigation systems that make possible determination of a ship’s position at any point are being developed for navigation on the open ocean. The system of navigation satellites is extremely promising in this regard.

The development of navigational equipment is making possible automation of the acquisition and processing of navigational information and direct input of data into the control system to solve the problem of stabilization of the ship on a prescribed path. The development and use of autonomous inertial navigation systems on transport vessels is promising.

REFERENCES

Ukhov, K. S. Navigatsiia. Leningrad, 1954.
Shchegolev, E. Ia. Radiotekhnicheskie sredstva morskogo sudovozhdeniia. Leningrad, 1956.
Iakushenkov, A. A. “Sudovozhdenie i sviaz’.” In Problemy razvitiia morskogo flota. Leningrad, 1970.
Iushchenko, A. P., and M. M. Leskov. Navigatsiia, 2nd ed. Moscow, 1972.

B. P. KHABUR

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Navigation 

the movement of vessels along waterways. Distinctions are made between maritime, inland, and combined navigation and between commercial, fishing, and other navigation.

Ancient navigators used reference points on riverbanks, lake-shores, and seacoasts. Later, navigation on the open sea was made possible by the development of nautical astronomy, the use of the compass, and improvements in vessel design. Modern navigation is based on developed technical facilities—vessels and their equipment—and navigation services—port, hydrometeoro-logical, hydrographic, rescue, repair, and other services.

Hydrometeorological conditions, maritime law, and waterways themselves can place limitations on the extent of navigation. Northern seas and inland waterways in the temperate zone freeze in winter, tides cause changes in depths, and natural waterways may be too shallow for navigation in some areas. In basins that freeze in winter, icebreakers and vessels with improved reliability in ice conditions help make prolonged navigation possible. Dredging deepens waterways, and dams are constructed to regulate river levels. Hydrometeorological conditions may limit navigation for restricted-use vessels, for example, inland vessels entering roads.

Navigation procedures are regulated by national laws and international agreements.

E. G. LOGVINOVICH