How sailors used to determine their coordinates. How was the location of the ship determined?

Long before the advent of satellites and computers, various "cunning" devices helped sailors surf the oceans. One of the most ancient - the astrolabe - was borrowed from Arab astronomers and simplified for working with it at sea.

With the help of disks and arrows of this device, it was possible to measure the angles between the horizon and the sun or other celestial bodies. And then these angles were translated into the values of the earth's latitude. Gradually, the astrolabe was replaced by simpler and more accurate instruments. These are the transverse rail, quadrant and sextant, invented between the Middle Ages and the Renaissance. Compasses with divisions printed on them and which received an almost modern look back in the 11th century allowed sailors to navigate the ship directly along the intended course.

By the beginning of the 15th century, "blind reckoning" began to be used. To do this, logs were thrown overboard, tied to these ropes - lines. Knots were tied on the ropes after a certain distance. The sundial marked the time of unwinding the line. We divided the length by time and obtained, of course, very inaccurately, the speed of the vessel.

Latitude reading

In the Middle Ages, sailors determined their position relative to the equator, that is, latitude, by looking at the sun or at the stars. The angle of inclination of the celestial body was found using an astrolabe or a quadrant (figures below). Then they opened their table, which was called ephemeris, and determined the position of the ship from it.

Measurement of the height of celestial bodies

To measure the height of a celestial body, the navigator had to set a metal rail on this body, looking at the body, drive crossbars of different lengths along the rail until they reached the horizon line. Marks were marked on the rail with the values \u200b\u200bof the heights above the horizon, that is, above sea level.

Determination of longitude

Sailors tried to do this with a sundial and a line - a thick rope with tied knots. The elapsed time was determined by the amount of sand poured out in the clock, and the speed of movement was determined by the length of the line thrown overboard, wound on the ship's view. Multiplying the time of the daily transition by the speed, the distance traveled was obtained. Knowing where the ship started its journey from, in what direction and how much it traveled in a day, one could roughly imagine the movement in the east-west direction, that is, the change in longitude.

The ship pictured below is the Victoria. On it, Magellan and his team made the world's first trip around the world and returned home to Portugal in 1522. Their route is shown as a wavy line on the left on a map issued in 1543.

The art of navigating a ship the shortest way from port to port is called navigation. In other words, navigation is a way of laying the course of a vessel from the place of departure to the destination, controlling the course, and, if necessary, correcting it.

On the navigation bridge there are instruments and devices necessary to control the vessel. Navigational instruments - compasses, gyroazimuths, autoplotters, logs, lots, echo sounders, sextants and other devices, are designed to determine the position of the vessel and measure individual elements of its movement of the vessel.

compasses

A compass is the main navigational instrument used to determine the course of a vessel, to determine directions (bearings) to various objects. On ships, magnetic and gyroscopic compasses are used.

Magnetic compasses are used as backup and control devices. According to their purpose, magnetic compasses are divided into main and travel compasses.

The main compass is installed on the upper bridge in the center plane of the vessel, so as to provide a good view over the entire horizon (Fig. 3.1). The image of the scale of the card with the help of an optical system is projected onto a mirror reflector installed in front of the helmsman (Fig. 3.2).

Rice. 3.1. Master magnetic compass

A traveling magnetic compass is installed in the wheelhouse. If the main compass has a telescopic reference transmission to the helmsman's station, then the steering compass is not installed.

Rice. 3.2. Mirror reflector magnetic compass

The magnetic needle on the ship is affected by the ship's magnetic field. It is a combination of two magnetic fields: the Earth's field and the ship's iron field. This explains that the axis of the magnetic needle is located not along the magnetic meridian, but in the plane of the compass meridian. The angle between the planes of the magnetic and compass meridians is called deviation.

The compass kit includes: a bowler hat with a card, a binnacle, a deviation device, an optical system and a direction finder.

Lifeboats use a light, small compass that is not permanently fixed (Fig. 3.3).

Rice. 3.3. Boat magnetic compass

Gyrocompass - a mechanical indicator of the direction of the true (geographical) meridian, designed to determine the course of an object, as well as the azimuth (bearing) of the oriented direction (Fig. 3.4 - 3.5). The principle of operation of the gyrocompass is based on the use of the properties of the gyroscope and the daily rotation of the Earth.

Rice. 3.4. Modern gyrocompass

Gyro compasses have two advantages over magnetic compasses:

they show the direction to the true pole, i.e. to the point through which the axis of rotation of the Earth passes, while the magnetic compass indicates the direction to the magnetic pole;
they are much less sensitive to external magnetic fields, such as those generated by the ferromagnetic parts of a ship's hull.

The simplest gyrocompass consists of a gyroscope suspended inside a hollow ball that floats in a fluid; the weight of the ball with the gyroscope is such that its center of gravity is located on the axis of the ball in its lower part, when the axis of rotation of the gyroscope is horizontal.

Rice. 3.5. Gyrocompass repeater with direction finder mounted on a pelorus

The gyrocompass may give measurement errors. For example, a sharp change in course or speed causes deviation, and it will exist until the gyroscope has worked out such a change. Most modern ships have satellite navigation systems (such as GPS) and/or other navigation aids that feed corrections into the gyrocompass's built-in computer. Modern designs of laser gyroscopes do not produce such errors, since they use the principle of optical path difference instead of mechanical elements.

The electronic compass is built on the principle of determining coordinates through satellite navigation systems (Fig. 3.6). The principle of the compass:

based on signals from satellites, the coordinates of the receiver of the satellite navigation system are determined;
the moment of time at which the determination of the coordinates was made is detected;
a certain time interval is expected;
the location of the object is re-determined;
based on the coordinates of two points and the size of the time interval, the velocity vector is calculated:
- direction of movement;
- movement speed.

Rice. 3.6. Electronic compasses

echo sounder

The navigation echo sounder is designed for reliable measurement, visualization, registration and transmission to other systems of data on the depth under the keel of the vessel (Fig. 3.7). The echo sounder must operate at all vessel speeds from 0 to 30 knots, in conditions of strong aeration of water, ice and snow slush, crushed and broken ice, in areas with a sharply changing bottom topography, rocky, sandy or muddy ground.

Rice. 3.7. Sonar Pointer

Hydroacoustic echo sounders are installed on ships. The principle of their operation is as follows: mechanical vibrations excited in the vibrator-emitter propagate in the form of a short ultrasonic pulse, reach the bottom and, reflected from it, are received by the vibrator-receiver.

Echo sounders automatically indicate the depth of the sea, which is determined by the speed of sound propagation in water and the time interval from the moment the impulse is sent to the moment it is received (Fig. 3.8).

Rice. 3.8. The principle of operation of the echo sounder

The echo sounder should provide measurement of depths under the keel in the range from 1 to 200 meters. The depth indicator must be installed in the wheelhouse, and the recorder - in the wheelhouse or chart house.

To measure the depths, a hand lot is also used in cases of running the vessel aground, measuring the depths at the side while moored at the berth, etc.

A manual lot (Fig. 3.9) consists of a lead or cast-iron weight and a lotline. The kettlebell is made in the form of a cone 25 - 30 cm high and weighing 3 to 5 kg. A recess is made in the lower wide base of the weight, which is lubricated with grease before measuring the depth. When the lot touches the seabed, soil particles stick to the grease, and after lifting the lot, one can judge the nature of the soil from them.

Rice. 3.9. hand lot

The breakdown of the lotlin is made in metric units and is indicated according to the following system: flags of various colors are intertwined at tens of meters; each number of meters ending in 5 is marked with a leather stamp with axes.

In each five, the first meter is indicated by a leather stamp with one prong, the second by a stamp with two prongs, the third by three prongs, and the fourth by four.

lag

Around the end of the 15th century. a simple speed meter became famous - a manual log. It consisted of a wooden plank with a lead weight in the shape of 1/1 of a circle, to which a light cable was attached, having knots at regular intervals (most often 7 m). To measure the speed of sailing ships sailing in those days, the log, as an approximately constant mark on the surface of the water, was thrown overboard and the hourglass was turned, measuring a certain length of time (14 s). During the time that the sand was pouring, the sailor counted the number of knots that passed through his hands. The number of knots received during this time was converted into the ship's speed in nautical miles per hour. This way of measuring speed explains the origin of the expression "knot".

Log - a navigational device for measuring the speed of the vessel and the distance traveled by it. Mechanical, geomagnetic, hydroacoustic, induction and radio Doppler logs are used on sea vessels. Distinguish:

relative lags, measuring speed relative to water; and
absolute logs that measure speed relative to the bottom.

Hydrodynamic log - a relative log, the action of which is based on the measurement of the pressure difference, which depends on the speed of the ship. The basis of the hydrodynamic lag is made up of two tubes brought out under the bottom of the vessel: the outlet of one tube is directed to the bow of the vessel; and the outlet of the other tube is flush with the skin. Dynamic pressure is determined by the difference in water heights in the tubes and is converted by the lag mechanisms into indications of the ship's speed in knots. In addition to speed, hydrodynamic logs show the distance traveled by the ship in miles.

The induction lag is a relative lag, the principle of which is based on the relationship between the relative speed of a conductor in a magnetic field and the electromotive force (EMF) induced in this conductor. The magnetic field is created by the lag electromagnet, and sea water is the conductor. When the vessel moves, the magnetic field crosses the stationary sections of the aquatic environment, while an EMF is induced in the water, proportional to the speed of the vessel. From the electrodes, the EMF enters a special device that calculates the speed of the vessel and the distance traveled.

A hydroacoustic log is an absolute log that works on the principle of an echo sounder. There are Doppler and correlation hydroacoustic lags.

Geomagnetic lag - an absolute lag based on the use of the properties of the Earth's magnetic field.

Radio lag - a lag, the principle of which is based on the use of the laws of radio wave propagation.

In practice, the lag readings are noted at the beginning of each hour and, from the difference in readings, the navigation S in miles and the ship's speed V in knots are obtained. Logs have an error, which is taken into account by the lag correction.

Radio navigation instruments

The ship's radar station (RLS) is designed to detect surface objects and the coast, determine the position of the ship, ensure navigation in narrow spaces, and prevent ship collisions (Fig. 3.10).

Rice. 3.10. Radar screen

The radar uses the phenomenon of reflection of radio waves from various objects located on the path of their propagation, thus, the phenomenon of echo is used in radar. The radar contains a transmitter, a receiver, an antenna-waveguide device, an indicator with a screen for visual observation of echo signals.

The principle of operation of the radar is as follows. The station's transmitter generates powerful high-frequency pulses of electromagnetic energy, which are sent into space with the help of an antenna in a narrow beam. Radio pulses reflected from some object (ship, high bank, etc.) return in the form of echo signals to the antenna and enter the receiver. From the direction of the narrow radar beam that is currently reflected from the object, you can determine the bearing or heading angle of the object. By measuring the time interval between sending an impulse and receiving a reflected signal, you can get the distance to the object. Since the antenna rotates during the operation of the radar, the emitted impulse oscillations cover the entire horizon. Therefore, an image of the situation surrounding the vessel is created on the display screen of the ship's radar. The central luminous dot on the radar indicator screen marks the position of the vessel, and the luminous line extending from this point shows the course of the vessel.

The image of various objects on the radar screen can be oriented relative to the center plane of the ship (heading stabilization) or relative to the true meridian (north stabilization). The "visibility" range of the radar reaches several tens of miles and depends on the reflectivity of objects and hydrometeorological factors.

Ship radars make it possible to determine the course and speed of an oncoming vessel in a short period of time and thus avoid a collision.

Rice. 3.11. ARPA screen

All ships must provide radar plotting on the radar screen, for this they are equipped with an automatic radar plotting system (ARPA). ARPA performs the processing of radar information and allows you to perform (Fig. 3.11):

manual and automatic capture of targets and their tracking;
display on the screen of the indicator of vectors of relative or true movement of targets;
identification of dangerously approaching targets;
indication on the board of movement parameters and elements of target rendezvous;
playing the maneuver with the course and speed for a safe divergence;
automated solution of navigation tasks;
display of elements of the content of navigation charts;
determining the ship's position coordinates based on radar measurements.

The Automatic Information System (AIS) is a maritime navigation system that uses mutual exchange between ships, as well as between the ship and the coast service to transmit information about the call sign and name of the ship for its identification, coordinates, information about the ship (size, cargo, draft, etc.). ) and its voyage, movement parameters (course, speed, etc.) in order to solve the problems of preventing collisions of ships, monitoring compliance with the navigation regime and monitoring ships at sea.

Electronic Chart Navigational Information Systems (ECDIS) are an effective means of navigation, significantly reducing the workload on the watch officer and allowing you to devote maximum time to observing the environment and making informed decisions on ship management (Fig. 3.12).

Rice. 3.12. ECDIS

Main features and properties of ECDIS:

carrying out preliminary laying;
checking the route for safety;
maintenance of executive laying;
automatic ship control;
display of "dangerous isobath" and "dangerous depth";
recording information in an electronic journal with the possibility of further playback;
manual and automatic (via the Internet) proofreading;
alarm when approaching a given isobath or depth;
day, night, morning and twilight palettes;
electronic ruler and fixed marks;
basic, standard and full load display;
an extensive and complementary base of marine objects;
base of tides in more than 3000 points of the World Ocean.

A satellite navigation system is a system consisting of ground and space equipment designed to determine the location (geographical coordinates), as well as movement parameters (speed and direction of movement, etc.) for land, water and air objects (Fig. 3.13) .

Rice. 3.13. GPS indicator

GPS is the Global Positioning System, a global navigation satellite positioning system. The system includes a constellation of low-orbit navigation satellites, ground-based tracking and control facilities, and a wide variety of those used to determine coordinates. The principle of determining one's place on the earth's surface in the global positioning system is to simultaneously measure the distance to several navigation satellites (at least three) - with known parameters of their orbits at each moment of time, and calculate their coordinates from the changed distances.

Navigation tools

Navigational sextant is a goniometric tool (Fig. 3.14), which serves:

in nautical astronomy - to measure the heights of luminaries above the visible horizon;
in navigation - to measure the angles between terrestrial objects.

Rice. 3.14. sextant

The word "sextant" comes from the Latin word "sextans" - the sixth part of the circle.

A marine chronometer is a high-precision portable watch that allows you to get a fairly accurate GMT at any time (Fig. 3.15).

Rice. 3.15. Chronometer

Ship time is determined by the meridian of the vessel's location and is most often corrected at night by the watch officer. So, for example, when the longitude changes by 15 ° to the east, the clock is moved forward 1 hour, and when the longitude changes by 15 ° to the west - 1 hour ago.

In order to have an accurate and uniform time indication in the engine room, crew mess, cabins, saloons, bars, galley, an electric clock is installed, corrected from the main clock located on the bridge.

Rice. 3.16. Interlining tool

Gasketing tools include (Fig. 3.16):

measuring compass - for measuring and postponing distances on the map;
parallel ruler - for drawing straight lines on the map, as well as lines parallel to a given direction;
navigational protractor - for plotting and measuring angles, courses and bearings on the map.

In addition, there are magazines, folders with documentation, navigation maps, mandatory reference books and manuals, etc. on the bridge (Fig. 3.17).

Rice. 3.17. Documentation

GPS

astrolabe

rail, quadrant and sextant

tench

Navigators' assistants

The most important thing for any vessel is to know its exact position at sea. At any point in time. The safety of the vessel itself, the cargo and the entire crew depends on this. I will not discover America if I say that at present the ship is controlled by a computer. Man only controls this process. In this article, I will talk about navigation assistants - satellite navigation systems that help ships get the exact coordinates of their position. I will also tell you what instruments the ancient navigators used. Now all ships are equipped with GPS receivers - global positioning system. Flying around our planet, navigation satellites continuously send streams of radio signals to it. These satellites belong to the US Naval Navigation Satellite System (VMNSS) and, more recently, the US Global Positioning System (GNS or GPS). Both systems enable ships at sea, day and night, to determine their coordinates with great accuracy. Almost up to a metre.

The principle of operation of both VNSS and GSM is based on the fact that a special GPS receiver on board the ship catches radio waves sent by navigation satellites at certain frequencies. The signals from the receiver are continuously sent to the computer. The computer processes them, supplementing them with information about the time of transmission of each signal and the position of the navigation satellite in orbit. (Such information gets to VNSS-satellites from ground tracking stations, and GSM-satellites have time and orbit reference devices on board). Then the navigation computer on the ship determines the distance between them and the satellite flying in the sky. The computer repeats these calculations at certain intervals and eventually receives data on latitude and longitude, that is, its coordinates.

But how did the ancient navigators determine the location of the vessel at sea? Long before the advent of satellites and computers, sailors were helped to surf the oceans by various "cunning" devices. One of the most ancient astrolabe- was borrowed from Arab astronomers and simplified for working with him at sea. With the help of disks and arrows of this device, it was possible to measure the angles between the horizon and the sun or other celestial bodies. And then these angles were translated into the values of the earth's latitude.

Gradually, the astrolabe was replaced by simpler and more accurate instruments. It is invented between the Middle Ages and the Renaissance cross rail, quadrant and sextant. Compasses with divisions printed on them and which received an almost modern look back in the 11th century allowed sailors to navigate the ship directly along the intended course.

By the beginning of the 15th century, “blind reckoning” began to be used. For this, logs tied to these ropes were thrown overboard - tench. Knots were tied on the ropes after a certain distance. By sun or hourglass, the time of unwinding the line was noted. We divided the length by time and obtained, of course, very inaccurately, the speed of the vessel.

Sailors of the past used such simple devices. By the way, today's ships also have a sextant. In a box, lubricated. And always new. True, this device is rarely used by anyone. GPS systems and computers have replaced the old proven navigational devices. On the one hand, this is normal. Progress. And on the other hand... A favorite phrase of some captains: "What will you do, comrades shipbreakers, when the satellites fail and the entire GPS system grunts"? We will re-master the sextant. But I hope that such a disgrace will not happen. For I really would not like to be in instead of, for example, one fine morning.

P.S. Photos belong to their rightful owners. Thank you kind people.

Page 2 of 2

So was the information contained in the portolans reliable? I think that it depended on the tasks assigned to them. For solving "local" applied problems - getting from point A to point B - they were quite suitable. Navigation in the Mediterranean was fairly well understood, as it was constantly supported by major pilot schools, such as the Genoese, Venetian or Lagos. For the knowledge of the whole world, portolans were completely unsuitable, more confusing researchers than helping them.

Only from the end of the 13th century, the first attempts at ocean navigation, as well as the wider use of the compass, revealed the need for a real display on a flat sheet of paper of the relief of the coast, indicating the winds and the main coordinates.

After the 14th century, portolans are often accompanied by rough contour drawings of the Mediterranean coast and the Atlantic coasts of Western Europe. Gradually, ships leaving for ocean voyages begin to be included in the work of compiling more accurate portolans and drawings.

Somewhere by the beginning of the 15th century, real navigation charts. They already represent a complete set of information for the pilot: coast relief, a list of distances, indications of latitude and longitude, landmarks, names of ports and local inhabitants, winds, currents and sea depths are indicated.

The map, the successor to the mathematical knowledge acquired by the ancients, the ever more accurate knowledge of astronomy, and thousands of years of experience in navigating from port to port, becomes one of the main fruits of the scientific thought of the pioneers: from now on, during long voyages, it is required to draw up reports necessary for a complete display of knowledge about the world. Moreover, the first ship's logs! Of course, sea travel has been described before, but now it is starting to become a regular occurrence. He was the first to introduce a mandatory log book for the captains of his caravels. The captains had to record daily information about the coast with the indication of coordinates - a matter extremely useful for compiling reliable maps.

Despite the desire to clarify and verify that moved the most famous cartographers (Fra Mauro in 1457 claimed that he could not fit into his map all the information that he managed to collect), fantasies, legends, fiction surrounded any cartographic work with a kind of “folklore” halo : on most maps dated before the 17th century, we see how, in place of little-known or insufficiently explored regions, images of various monsters appear, drawn from ancient and early Christian mythologies.

Quite often, the compiler, describing the inhabitants of remote corners, resorted to speculation. Areas that were explored and fell under the rule of European kings were marked with coats of arms and flags. However, the magnificently painted vast wind roses could not be useful if they were incorrectly oriented or marked in the wrong lines of "diamonds" (a primitive system of orientation that preceded the system of meridians and parallels). Often the work of a cartographer became a real work of art. At the courts of kings, planispheres were looked at like canvases, navigators set off on long journeys were guessed behind them, monsters caused shivers, the distances traveled and intriguing names fascinated. It took a long time before the custom of making a map decorative gave way to really useful cartography, devoid of all fiction.

This explains the incredulity with which the great navigators, and above all Christopher Columbus, belonged to the decorated maps of the 15th century. Most sailors preferred to rely on their knowledge of the winds, bottom topography, currents and observations of the celestial sphere, or tracking the movement of schools of fish or flocks of birds, in order to navigate the vast expanses of the ocean.

Undoubtedly, it was in the 15th century, thanks to the Portuguese navigators, and then the voyage of Columbus and, finally, the round-the-world voyage of Magellan in 1522, that humanity was able to test the calculations of the ancient Greeks and ideas about the sphericity of the Earth in practice. Many navigators now in practice received specific knowledge testifying to the sphericity of our planet. The curved line of the horizon, the shifting of the relative heights of the stars, the rise in temperature as we approached the equator, the change of constellations in the southern hemisphere - all this made obvious the truth that contradicted Christian dogma: the Earth is a ball! It remained only to measure the distances that had to be covered on the high seas in order to reach India, in a southerly direction, as the Portuguese did in 1498, or in a western direction, as it seemed to Columbus, when in 1492 he met an insurmountable obstacle in his path in face of the Americas.

Columbus was well acquainted with the cosmographic literature of that time. His brother was a cartographer in Lisbon, and he himself tried to build a globe on the basis of available atlases, modern and ancient treatises on cosmography. True, he made, following his Imago Mundi (1410), a gross mistake in estimating the distance between Portugal and Asia, underestimating it (there is a hypothesis that he did this deliberately). However, he heeded the advice of eminent cartographers such as (who believed in the sea route to the west), (the future Pope Pius II) and (later the author of a fairly accurate globe).

Beginning in 1435, Portuguese and Italian sailors made it a habit to sail at a distance from the African coast to avoid dangerous areas and changeable winds. The coastal zone, replete with reefs and shoals, indeed presented an obvious danger of shipwreck.

However, such a significant distance from the coast that it is lost from sight presupposes the ability to navigate the open sea in a flat, uniform space without lighthouses, limited only by the horizon line. And the sailors of the 15th century lacked the theoretical knowledge of mathematics and geometry necessary to accurately determine their location. As for measuring instruments, things were even worse with them. Until the 16th and 17th centuries, none of them were really good at what they did. The maps, although constantly updated, had significant gaps.

To appreciate the extraordinary courage of the navigators who explored the near and then the far Atlantic, one must remember what miserable means they had at their disposal to determine their location on the high seas. The list will be short: the sailors of the 15th century, including Christopher Columbus, had practically nothing that would help them solve the three main tasks of any navigator going on a long voyage: to keep a course, measure the distance traveled, know with accuracy their present location.

The 15th-century sailor had only a primitive compass (in various variations), a crude hourglass, buggy charts, approximate declination tables, and, in most cases, erroneous ideas about the size and shape of the Earth! In those days, any expedition across the ocean became a dangerous adventure, often fatal.

In 1569 Mercator made the first map conformal cylindrical projection, and the Dutch Luca Wagener brought into use atlas. This was a major step in the science of navigation and cartography, because even today, in the twenty-first century, modern nautical charts are compiled in atlases and made in the Mercator projection!

In 1530 a Dutch astronomer Gemma Frisia(1508-1555) in his work “Principles of Astronomical Cosmography” proposed a method for determining longitude using a chronometer, but the lack of sufficiently accurate and compact clocks left this method purely theoretical for a long time. This method has been named chronometric. Why did the method remain theoretical, because the clock appeared much earlier?

The fact is that watches in those days could rarely go without stopping during the day, and their accuracy did not exceed 12-15 minutes a day. And the clock mechanisms of that time were not adapted to work in conditions of sea rolling, high humidity and sudden changes in temperature. Of course, in addition to mechanical ones, sand and sundials were used in maritime practice for a long time, but the accuracy of the sundial, the winding time of the hourglass were completely insufficient for the implementation of the chronometric method for determining longitude.

Today it is believed that the first accurate clock was assembled in 1735 by an Englishman John Harrison(1693-1776). Their accuracy was 4-6 seconds per day! At that time it was simply fantastic accuracy! And what's more, the watch was adapted for sea travel!

Ancestors naively believed that the Earth rotated uniformly, lunar tables were inaccurate, quadrants and astrolabes introduced their own error, so the final errors in calculating coordinates were up to 2.5 degrees, which is about 150 nautical miles, i.e. almost 250 km!

In 1731, an English optician improved the astrolabe. The new device, called octant, made it possible to solve the problem of measuring latitude on a moving ship, since now two mirrors made it possible to simultaneously see both the horizon line and the sun. But the octant did not get the glory of the astrolabe: a year earlier, Hadley had designed sextant- a device that made it possible to measure the position of the vessel with very high accuracy.

The fundamental device of a sextant, i.e. a device that uses the principle of double reflection of an object in mirrors, was developed back in Newton, but was forgotten and only in 1730 was reinvented by Hadley independently of Newton.

The marine sextant consists of two mirrors: an index mirror and a stationary translucent horizon mirror. Light from a luminary (star or planet) falls on a movable mirror, is reflected on the horizon mirror, on which both the luminary and the horizon are visible at the same time. The angle of inclination of the pointing mirror is the height of the luminary.

Since this site is about history and not about navigation, I will not go into details and features of various navigational instruments, but I want to say a few words about two more instruments. These are lot() and lag().

In conclusion, I would like to briefly dwell on some historical dates in the history of the development of navigation in Russia.

One thousand seven hundred and first year is perhaps the most significant date in domestic navigation, since this year the emperor Peter I issued a decree on the establishment of "Mathematical and Navigational, that is, nautical cunning sciences of learning." Year of birth of the first national navigation school.

Two years later, in 1703, the teacher of this school compiled the textbook Arithmetic. The third part of the book is entitled "Generally about the earthly dimension, and even belongs to navigation."

In 1715, the senior classes of the school were transformed into the Naval Academy.

1725 is the year of birth of the St. Petersburg Academy of Sciences, where such luminaries of science taught as, Mikhail Lomonosov(1711-1765). For example, it was Euler's astronomical observations and mathematical description of the motion of the planets that formed the basis of high-precision lunar tables for determining longitude. Bernoulli's hydrodynamic studies made it possible to create perfect logs for accurately measuring the speed of a ship. Lomonosov's works dealt with the creation of a number of new navigation instruments, which served as prototypes for instruments that are still in use today: course plotters, recorders, logs, inclinometers, barometers, binoculars...

Vessel positioning

Let's talk about a few simple, but very necessary, ways to determine the location of a yacht in the sea. The task is simple, but extremely important for your safety. It can be roughly divided into two cases:

1. You are sailing within sight of the shores and navigation marks that are marked on your chart.
2. You are sailing a yacht on the high seas in the absence of any landmarks.

By the way, if the course passes near the coast, but in conditions of limited visibility (for example, at night or in dense fog), then the method of determining the location will most likely refer to the second case.

So, we are making a coastal voyage and the yacht does not lose sight of the land (or signs of navigational conditions). It is important for us that at the moment of determining our location, we see the required number of landmarks that we can identify on the map.

There is another issue that needs to be discussed. We live in the 21st century, and the development of electronic navigation aids has reached fantastic heights. And if you rely only on electronics, then navigation turns out to be no more difficult than a computer game - you only need to study the instructions attached to the device.

But pay attention to one circumstance: according to the laws of any country, all ships going to sea - merchant, military and sports, sailing and motor - are required to have on board a complete set of traditional navigation aids: a set of paper charts, a laying tool, a sextant, sailing directions and etc. Navigators, skippers and captains are required to plot on traditional charts during any sea passage. I must say that I fully agree with this order. It must be understood that the sea is an element hostile to man, and he is alone with it.

Is it really possible to unconditionally entrust the lives of people on board, the life and fate of the yacht to a small plastic box with electronic filling?! Sea air is a very aggressive environment, which sooner or later will disable fine microelectronics; sooner or later you will forget to take on board a spare set of batteries for her; on the GPS can get sea spray, rain; lightning can strike a mast and disable all electronics - after all, according to the theory of reliability, any device can fail on its own - and what to do?

Life has shown that knowledge of navigation and stable skills in navigation by traditional methods are simply necessary for any person who goes to sea as a navigator, skipper or captain.

Therefore, let's move on, in fact, to the methods of determining the location of the vessel using traditional methods.

1. Reckoning, or Dead Reconing

Imagine that the yacht is sailing on the open sea and there are no visible landmarks. To understand the principle of the method, suppose that at 10.00 our yacht was at point A, which we have plotted on the map. The speed of the yacht is 7 knots (we read it from the ship's log), the true course is 045ºT (they counted from the directional compass and took into account the magnetic declination). We want to determine where the yacht will be at 11.30. Naturally, according to the conditions of our problem, from 10.00 to 11.30 the yacht sails without changing course (045ºT) ( see fig. one), at a constant speed (7 knt). The distance traveled is calculated by the elementary formula:
D = S X t, where
D– distance traveled in miles;
S is the speed of the boat in knots;
t- time in hours.
D = 7knt x 1.5 = 10.5 n.m.

Rice. 2

This is, in the simplest case, the calculated location of our yacht (indicated by the + sign and the letters DR with time).

Rice. 3

But this method can be used in the case when the previous coordinates of the yacht are known exactly ( fix), its speed and heading, and there is no drift associated with wind and currents.

2.Estimate Position (EP)

If the direction and speed of the current are known, we can plot the location of the yacht on the map using a simple graphical method. Suppose, when calculating DR in step 1 ( see fig. 4) we learned from the atlas of tidal currents that from 10.00 to 11.30 in the navigation area there was a current with a speed of 3 knots and a direction of 110ºT. Please remember that the current always flows "in" the indicated direction, unlike the wind, which always blows "out" of the indicated direction.

Rice. 4

So, using the principle of independence of motions, known from the school physics course (he says that any movement of the body can be represented as a vector sum of simple rectilinear displacements), from the point DR 11.30 we will postpone with the help of the plotter the direction 110ºТ ( see fig. 5). Please note that the current vector is denoted exactly as in the figure.

Rice. 5

Then we calculate the length of the vector, the time of the yacht’s movement: 1.5 hours = 90 min, the current speed is 3 knots ( knts). This means that during the movement from 10.00 to 11.30 the yacht moved in the direction of 110ºT under the influence of the current by: 3 knots x 1.5 hours = 4.5 nautical miles. Set aside on a segment measuring 4.5 n.m. and get a point EP 11.30 (standard symbol) ( see fig. 6). This is the calculated position of our yacht at 11.30, which from 10.00 from point A was moving on a course of 045ºT at a speed of 7 knt under the influence of the current direction 110ºT and speed 3 knt. Further laying the course, we must do already from the point EP 11.30. We also completed the task - we know where the yacht is.

Rice. 6

3.FIX

The specific position of a vessel at a given time is denoted by the English term FIX. There are many ways to define it. We will consider the most widely used and general way: finding FIX-A on two or more compass bearings (preferably three).

Let's say our yacht is heading 0ºE (360º) at a speed of 7 knots. You pass a section of the coast where you can clearly and distinctly see the lighthouse A, Lighthouse V and a small island WITH. The time is 10.15 and the last EP was determined at 9.30 ( see fig. 7).

Rice. 7

Turning to the map of the area, you must absolutely accurately identify the selected landmarks A, B and WITH with their image on the map. (All land features depicted on a navigation chart are clearly visible from the sea (day and night) and can be used for navigation.) Charts always show lighthouses, water towers, tall, free-standing buildings, radio masts, etc. visible from the sea.

Using a manual direction finder compass, we will take magnetic bearings to selected landmarks A, B and WITH (see fig. eight). We understand that in order to map a magnetic bearing, we must convert it to true bearing using a declination correction.

Rice. eight

Recall the rule: when moving from a magnetic bearing to a true bearing, the western declination is subtracted, and the eastern declination is added.

Let's assume that after we took the bearings one by one to the lighthouse A, Lighthouse V and the island and converted them into true bearings, we got the following values:

True bearing to the lighthouse A– 045ºT
True bearing to the lighthouse V– 90ºT
True bearing to the island WITH– 135ºT

With the help of the plotter, we set aside these true bearings from our objects A, B, C, as shown in rice. 9.

Rice. 9

As we can see, the bearings did not intersect at one point, but formed a kind of triangle ( hat). This was due to small errors in taking bearings. But we can say that the yacht is at 10.15 somewhere inside this triangle. For our purposes, this accuracy is quite enough - we found FIX. Remember, please, a few rules that must be observed in order to FIX your yacht was as accurate as possible:
1. choose the nearest, more clearly visible objects for taking bearings;
2. try to keep the angles between objects not too sharp or too obtuse (optimal angles are in the range of 30-110º);
3. take bearings as accurately as possible;
4. If the speed of the yacht is high (for example, a motor yacht), then try to take bearings for as little time as possible in order to reduce the error caused by the movement of the yacht during this time.

Of course, there are many more ways to define FIX, for example, with the help of a radar, using leading objects, the height of objects measured by a sextant, astronomical methods, etc. These methods are beyond the scope of our course for dummies.

Perhaps it is necessary to mention the simplest way of taking FIX via GPS- your GPS it will simply show you the coordinates of the vessel - plot them correctly on the map and set the time.

Navigation for dummies. (Lesson 4)

Rescue cruise bearing

A very experienced yachtsman once told me that many years ago, on a small yacht, he got into a five-day storm in the Mediterranean Sea. The yacht's electrical equipment failed on the second day of the storm due to a lightning strike, a pocket battery GPS exhausted their resource a little later, the sky was covered with clouds, so there was no opportunity to get a fix using celestial navigation, and how to use a sextant on a small yacht (32 feet) with a wave height of 5-6 meters ?! For five days and nights, a wind of force 8-9 raged and changed its direction several times, and the only thing that could be said with certainty about the location of the yacht was that it was somewhere in the Mediterranean Sea.

And then on the fifth evening, through the rain and splashing waves, the skipper noticed a gleaming red light. Noticing the period of fire, the skipper determined the lighthouse using the light guide, and then, despite the strong sea, using the cruise-bearing method, determined his position with an accuracy of one nautical mile!

So, we have only one visible object that we can reliably identify on the map. Within our visibility, for example, one lighthouse or a sign of navigational conditions, or a small island, a cape, a rock, a radio mast.

In this case, to determine the position of the yacht, we can use a method called running fix, or cruise bearing. The method is based on the fact that we take two bearings for one object at different times. A necessary condition for the application of this method is that the boat's speed and heading must be maintained for at least the time interval between taking the first and second bearing to this object.

Let's see how this looks in practice. Suppose our yacht is on a true course of 080°T at a speed of 8 knots. We clearly and clearly see the rock ( rock) indicated on our map. Using a direction finder compass ( hand bearing compass) at 0900 we take the bearing to this rock and, taking into account the magnetic declination, we recalculate it to the true one and put it on the map. Please note that we plot the course (080°T) on the map at an arbitrary location, since we do not yet know where the yacht is.

Suppose the first bearing taken by us at 0900 is 45°M. Let's set the magnetic declination equal to 07 ° 30 "W. We recalculate the magnetic bearing into true: 045 ° M - 07 ° 30" W \u003d 37 ° 30 "T. Put it on the map. We continue to walk, say, 30 minutes, trying to keep as accurate as possible heading 080 ° T and maintaining a speed of 8 knots. At 0930 we take the second bearing to this rock. Suppose it is 015 ° M. Convert it to true: 015 ° - 07 ° 30 "= 07 ° 30" T and put on the map - see pic 1.

Rice. one

In 30 minutes (the time between taking the first and second bearings), our yacht covered 4 nautical miles on a course of 80°T. On the course line from the point of its intersection with the first bearing, we set aside the distance traveled (4 nautical miles). We transfer the first bearing parallel to itself to this point. The point of intersection of the bearing taken at 0930 and the transferred bearing is our boat's position at 0930, or RF 0930 ( running fix), --see fig. 2 and rice. 3.

Rice. 2

Rice. 3

The accuracy of this method depends on how accurately you can keep your course, speed and, of course, how accurately you can take two bearings. On relatively calm water and with a well-calibrated log, this method can be used to obtain a fix with almost accuracy. GPS.