Every schoolchild knows very well that the nautical mile is a unit of measurement, which is used to calculate the distance over large expanses of water. Nowadays, this value is not included in the international system. physical units, however, it is widely used by almost all peoples, both European and American. That is why in various sources you can find different designations for this indicator. Among them there are NM, nmi and others.
The history of the origin of the nautical mile
The nautical mile appeared around the Renaissance. Then the sailors calculated the distances that they had to sail on ships, based on the characteristics of the arcs of the meridians of the earth. So this naval unit of distance was equal to the length of one degree of the meridian arc, and was calculated using a complex mathematical formula. However, due to the fact that our planet had and has the shape of an ellipse, this angular minute in practice was not constant. Since the radius of curvature at certain latitudes of the ellipsoid is different, then such a value as a nautical mile would be the smallest in the equator and the largest at the poles of the Earth.
Final acceptance of a given metric unit
In this regard, in the twentieth century, in particular in the USSR, the average standard unit for measuring distance in the sea was adopted. An angle of 45 degrees was taken as the basis for the formula by which this value was calculated, and the result was a number equal to 1852 meters. Despite the fact that a nautical mile can be converted into units of measurement so familiar to us, it is not used as metric... Since it is based on one degree of the arc of the meridian of our planet, it becomes an angular unit of measurement. In matters related to shipping, especially over fairly long distances, this is very convenient and acceptable.
Mathematical division of one mile
As we can see, the total nautical mile is almost two kilometers. In some cases, for sea travel, this value is too large. That is why this value was divided into cable ones. There are 10 cables per mile, which in turn equals one third of the nautical league. This value is not used in shipping and in other sciences, but sometimes it serves as a guideline that allows you to make more accurate calculations, to lay a more detailed and correct sea route.
What other miles are there?
Knowing the features of American units of measurement, many people are confused about what is equal to 1 nautical mile. In this country, this measure is used not only in shipping, but also overland distances. One US mile, which is often used to indicate the speed of a vehicle and the distance it travels, is 1,609.344 meters. It is also worth noting that in this country, in some cases, there are differences in nautical units of length measurement. So, the nautical mile in the states in some documents is equal to 1853.249 meters. However, if it is necessary to export the cargo according to documents concluded with the countries of Europe and Asia, then it is the international measurement system that was recognized as official in 1929.
Back in the days of the ancient Romans, one land mile was equal to 1000 steps. Later, a specific figure was established - 1609 meters. The length of the nautical mile was 1,852 meters. Where did this come from?
A bit of history ...
In order to measure the speed of the ship, it was inconvenient for sailors to use land miles... Especially, there were unjustified risks during emergency work. From the raging elements during the storm, the life of the sailors was in great danger. Under such conditions, it was not possible to use land measurements.
Therefore, we found more suitable option... They took a heavy log and threw it overboard. Then they counted how many knots would pass through the sailor's hands in a certain period of time before the rope was pulled.
Empirically determined the distance between the nodes and the time interval. There are different versions about precise definition... One of them was when the distance between nodes averaged 15 meters. It took 30 seconds.
It was practical and rational. The countdown was measured with an hourglass. All that remained was to count the knots and look at the sand. Even an illiterate sailor could complete the task.
Summed up these studies and found out. The length from one knot to another until the rope is pulled is 15 meters, in time it takes 30 seconds. Simple arithmetic operations calculated average speed ship. Thus, one nautical mile was 1852 meters in one hour.
Further developments
With the development of navigation, even greater convenience was introduced. One nautical mile became equal to one minute along the meridian. 1 degree equals 60 minutes. It will take 60 nautical miles. The nautical mile has become convenient for calculating navigation problems.
Therefore, the navigators began to measure the distance with a compass. Applying it to the scale, they recognized the distance in nautical miles. For example, to find out a distance of 30 miles, 30 arc minutes is enough with a compass on any meridian plotted on the map.
Now, of course, all equipment is computerized. There is no need to use outdated methods, but the nautical mile, as a unit of measure for distance, remained unchanged at 1852 meters. It is called navigational or geographic.
The knot is used in shipping as the basic unit of speed. Nautical miles and knots are the same understandable and familiar measurements at sea as kilometers and meters on land.
Sources:
- Units. What is the SI system?
- Why are nautical miles different from land miles, and sea and land kilometers are the same?
- Why is a nautical mile different from a land mile?
- What is a nautical mile and what is a nautical knot?
Speed on land is measured in the unit of time spent on the passage of one kilometer - kilometers per hour. On the water, speed is measured in knots - special units characteristic only of navigation.
According to encyclopedic dictionaries, a knot is a measure of length equal to 1 sea or 1852 meters. Thus, a ship traveling at a speed of one mile per hour or 1 knot per hour covers a distance equal to one kilometer and 852 meters per hour. What is the reason for such, at first glance, strange peculiarities of measuring in shipping and?
Node birth
What does nautical mile mean?
A nautical mile is approximately two kilometers, or more precisely, 1852 meters. In big Soviet encyclopedia»Mentions that this value was approved in 1929 at the International Hydrographic Conference. It is considered true in the CIS countries and a number of other states, although it is not included in the list international system units.
Where does the meaning come from? It is known that the distance of 1853 meters is the approximate linear length of one minute of latitude, that is, 1/60 of the meridian arc. It should be noted that this length of the meridian corresponds only to middle latitudes the globe... We add that a nautical mile contains 10 cables.
The value of the nautical mile in Great Britain was slightly different, where until 1929 it was considered to be 1853 meters. This was due to the convenience of converting an ordinary mile into a sea mile. In this case, it was enough to add 800 to the mile to get a nautical mile in feet.
What does sea knot mean?
The nautical node displays the specific speed of the vessel. A ship that traveled one nautical mile per hour made one nautical knot. The number of nautical miles that a ship travels in one hour is equal to the number of nodes. Moreover, it is not customary to talk about the speed of the vessel as the number of knots per hour. If it is indicated that a ship makes twelve knots, it is implied that the number of miles it covers in sixty minutes.
Why did the sea knot get this name? It turns out that this concept is associated with a marine device, which previously measured the speed of the vessel - lag. The lag was a long load that was thrown overboard. The rope was previously knotted in 50-foot increments. After that, the captain or his assistant counted the number of knots on the cable that would submerge in the water in a certain time. Their number also corresponded to the speed of the vessel.
Nowadays, the speed of a vessel in knots is rarely measured, only in Britain it is customary to talk about sea per hour. In most countries, sea transport speeds are measured in kilometers per hour.
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Miles accrual rules
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4. Marine length and speed measures
The unit of measure for distance at sea is a nautical mile, equal to the linear length of one minute of the meridian, that is, one minute of latitude. In the USSR and a number of other countries, a mile is adopted equal to 1852.3 m(6,080 feet). 1/10 of a mile is called cables, it is equal to 185.2 m. When solving practical problems of navigation, the standard international mile is taken, the length of which is taken equal to 1852 m, which corresponds to the arc length of one minute of the meridian in the middle latitudes of the hemisphere. The following units can also be used to measure distances at sea:
The speed of a ship is measured by the number of miles traveled by it in 1 hour. The unit of speed "mile per hour" is called a knot. You cannot say: "The speed of the ship is 15 knots per hour." It should be said: "Speed 15 knots."
Currently, a reform is underway to replace miles and knots by kilometers and kilometers per hour, respectively.
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4. Marine length and speed measures.
At sea, a nautical mile is taken as a unit of distance. A nautical mile is equal to one minute of the earth's meridian arc; the value of this minute on the mercator map depends on the latitude of the place. On the map, the linear value of one mile changes in proportion to sec f (secant of latitude).
Table 1
VISIBLE HORIZON RANGE IN MILES AND KILOMETERS DEPENDING ON THE HEIGHT OF THE OBJECT.
|
Height, m |
Visible horizon range |
Height, m |
Visible horizon range |
Height, m |
Visible horizon range |
|||
|
miles |
km |
miles |
km |
miles |
km |
|||
|
0. 3 |
1, 2 |
2, 1 |
7, 6 |
5, 7 |
10, 6 |
19, 8 |
9, 3 |
17, 2 |
|
0, 6 |
1, 6 |
3, 0 |
7, 9 |
5, 9 |
10, 9 |
21, 3 |
9, 6 |
17, 8 |
|
0, 9 |
2, 0 |
3, 7 |
8, 2 |
6, 0 |
11, 0 |
22, 1 |
9, 9 |
18, 3 |
|
1, 2 |
2, 3 |
4, 3 |
8, 5 |
6, 1 |
11, 2 |
24, 4 |
10, 3 |
19, 0 |
|
1, 5 |
2, 6 |
4, 8 |
8, 8 |
6, 2 |
11, 4 |
25, 9 |
10, 6 |
19, 6 |
|
1, 8 |
2, 8 |
5, 2 |
9, 1 |
6, 3 |
11, 6 |
27, 4 |
10, 9 |
20, 2 |
|
2, 1 |
3, 0 |
5, 6 |
9, 4 |
6, 4 |
11, 8 |
29, 0 |
11, 2 |
20, 7 |
|
2, 4 |
3, 3 |
6, 1 |
9, 8 |
6, 5 |
12, 0 |
30, 5 |
11, 5 |
21, 3 |
|
2, 7 |
3, 5 |
6, 5 |
10, 1 |
6, 6 |
12, 2 |
32, 5 |
11, 8 |
21, 8 |
|
3, 0 |
3, 6 |
6, 7 |
10, 4 |
6, 7 |
12, 4 |
33, 5 |
12, 1 |
22, 4 |
|
3, 4 |
3, 8 |
7, 0 |
10, 7 |
6, 8 |
12, 6 |
35, 1 |
12, 3 |
22, 8 |
|
3, 7 |
4, 0 |
7, 4 |
11, 0 |
6, 9 |
12, 8 |
36, 6 |
12, 6 |
23, 3 |
|
4, 0 |
4, 1 |
7, 6 |
11, 3 |
7, 0 |
13, 0 |
38, 1 |
12, 8 |
23, 7 |
|
4, 3 |
4, 3 |
8, 0 |
11, 6 |
7, 1 |
13, 1 |
39, 6 |
13, 1 |
24, 4 |
|
4, 6 |
4, 5 |
8, 3 |
11, 9 |
7, 2 |
13, 3 |
41, 2 |
13, 3 |
24, 6 |
|
4, 9 |
4, 6 |
8, 5 |
12, 2 |
7, 3 |
13, 4 |
42, 7 |
13, 6 |
25, 2 |
|
5, 2 |
4, 7 |
8, 7 |
12, 5 |
7, 4 |
13, 6 |
44, 2 |
13, 8 |
25, 6 |
|
5, 5 |
4, 9 |
9, 1 |
13, 1 |
7, 5 |
13, 9 |
45, 7 |
14, 1 |
26, 0 |
|
5, 8 |
5, 0 |
9, 3 |
13, 4 |
7, 6 |
14, 1 |
48, 8 |
14, 5 |
26, 8 |
|
6, 1 |
5, 1 |
9, 5 |
13, 7 |
7, 7 |
14, 2 |
51, 8 |
15, 0 |
27, 8 |
|
6, 4 |
5, 3 |
9, 8 |
14, 0 |
7, 8 |
14, 4 |
54, 9 |
15, 4 |
28, 5 |
|
6, 7 |
5, 4 |
10, 0 |
14, 9 |
8, 0 |
14, 8 |
57, 9 |
15, 8 |
29, 2 |
|
7, 0 |
5, 5 |
10, 2 |
16, 8 |
8, 5 |
15, 7 |
61, 0 |
16, 2 |
30, 0 |
|
7, 3 |
5, 6 |
10, 4 |
18, 3 |
8, 9 |
16, 5 |
|||
Therefore, it is recommended to measure the distance on the map using a compass, then applying it to the vertical frames of the map at the same latitude as the measured distance. For practical purposes of navigation in the USSR, the following are adopted: standard nautical mile equal to 1852 m; cables - one tenth of a nautical mile (185.2 m); fathom - one hundredth cable (1.85 m, or 6 feet). Fathoms and feet are used to measure depths in England and partly in the United States. Most other countries use meters (one foot equals 305 mm).
The kilometer is the basic unit of measure for distance in rivers, lakes, and reservoirs. It is equal to 1000 m, or 0.54 nautical miles. Vessel speed is measured in knots. One knot corresponds to the speed at which the vessel travels one mile in one hour.
5. True heading and bearing, heading angle.
Rice. 41. Graphical determination of the true heading of the vessel and the true bearing of the subject
The true heading of a vessel IR is the angle between the northern part of the true meridian (lines NS ) and the diametrical plane of the vessel (direction of the bow of the vessel). The diametrical plane of the vessel DP is called the longitudinal vertical plane dividing the vessel into two symmetrical equal parts. True heading is counted clockwise from 0 ° to 360 °.
The true bearing of the IP object is the angle measured from the nordic part of the true meridian clockwise to the direction to the object. Bearing is measured from 0 ° to 360 ° clockwise. On navigational charts, only the ship's true heading and true bearings are plotted (Fig. 41).
To determine directions to the sea, lake and reservoir, i.e. to determine the ship's course and bearings various subjects, serves as a compass. There are hydroscopic and magnetic compasses. The operation of a magnetic compass is based on the property of a magnetic needle to occupy a certain position in the earth's magnetic field, namely: the north end of the magnetic compass needle points to the north magnetic pole of the earth N M.
The magnetic and geographic poles do not match. The direction passing through the axis of the magnetic needle is called the magnetic meridian. The magnetic meridian does not coincide with the direction of the true meridian.
The angle between the north of the true meridian and the north of the magnetic meridian is called magnetic declination. d. Declination is measured from the northern part of the true meridian to the east or west from 0 to 180 °. The eastern, or skeleton, declension is assigned a plus sign, and the western, or vestibular, is assigned a minus sign. The magnetic declination for a given location is not constant; it constantly increases or decreases by a small constant value. The declination value in a given navigation area, its annual increase or decrease in the year to which the declination is reduced, are indicated on navigation charts.
For example, the title of the map reads: "The declination of the compass is given to 1970, 10 ° core, an annual increase of 3 arc minutes." If an amateur uses this map in 1972, then from 1970 to 1972 the declination increased by 6 arc minutes, that is, by 0.1 °, and therefore in 1972 the declination will not be 10 °, but 10.1 °. If there is no difference in declination on the track, at different sections according to the map data, then all sections of the track are processed in the same way.
In order, knowing the magnetic course of the MC or the bearing of the MP and the declination d of the compass in a given navigation area, to find the true course of the IR and the true bearing of the PI, it is necessary to algebraically add the declination given to the year of sailing with its sign to the magnetic course or bearing:
1) MK + (± d) = IR
and the inverse problem:
IR - (± d) = MK
2) MP + (± d) = PI or PI - (± d) = MP.
Rice. 42. Determining true bearing via heading angle or declination
Heading angle KU is the angle between the diametrical plane of the vessel and the direction to the object (Fig. 42). The heading angle is determined using a direction finder and is measured along the azimuth circle of a magnetic compass. It can be starboard or port side, changing from 0 to 180 °. In order to get the heading angle, you need to track the object using a direction finder and take a reading NS in the azimuth circle. If the object is on the port side, then the heading angle reading will be more than 180 °. The heading angle obtained in this case must be subtracted from 360 °.
The difference will be the value of the heading angle of the port side. The starboard heading angle has a plus sign, the port heading angle has a minus sign.
The true bearing can be determined through the heading angle using the formula:
PI = IR + KU p / b,
PI = IR - KU l / w.
If in the first case the true bearing is more than 360 °, then 360 ° must be subtracted from the result obtained. If, in the second case, the true heading is less than the heading angle, then 360 ° must be added to the true heading and the value of the angle must be subtracted from the result obtained.
In fig. 42 shows the correction of the magnetic bearing of the MF with declination d or heading angle to obtain the value of the true bearing of the MT to the beacon M. The line N M S M shows the direction of the magnetic meridian from which the magnetic bearing is measured. V this example it is 280 °. The declination is west 10 ° with a minus sign, so the true bearing will be:
1) PI = MP + (- 10 °), PI = 280 ° + (- 10 °) = 270 °.
2) PI = IR + KU p / b, PI = 225 ° + 45 ° = 270 °.
6. Deviation of the magnetic compass. Correction and translation of points.
Metal ship hull, various hardware, the motors are the cause of the deviation of the magnetic compass needle from the magnetic meridian, i.e. from the direction in which the magnetic needle should be located on land. The magnetic lines of force of the earth, crossing the ship's iron, turn it into magnets. The latter create their own magnetic field, under the influence of which the magnetic needle on the ship receives an additional deviation from the direction of the magnetic meridian.
The deflection of the needle under the influence of the magnetic forces of the ship's iron is called compass deviation. The angle between the nordic part of the magnetic meridian N M and the nordic part of the compass meridian N K is called the deviation of the magnetic compass s (Fig. 44).
Deviation can be either positive - eastern, or skeleton, and negative - western, or messenger. Deviation is a variable value and varies depending on the latitude and course of the ship, since the magnetization of the ship's iron depends on its location relative to the magnetic lines of force of the earth.
To calculate the magnetic heading of the MK, it is necessary to algebraically add the deviation s on the given heading to the value of the compass heading of the KK:
KK + (± s) = MK
or MK - (± s) = KK.
For example, compass heading QC equal to 80 °, while the deviation of the magnetic compass s = 20 ° with a plus sign. Then, using the formula, we find:
M K = KK + (± s) = 80 + (+ 20 °) = 100 °.
If the ship's own magnetic field is large, then the compass is difficult to use, and sometimes it stops working altogether. Therefore, the deviation must first be eliminated using compensation magnets located in the compass noctose and soft iron bars installed in the immediate vicinity of the compass.
After the destruction of the deviation, they begin to determine the residual deviation at various courses of the vessel. The destruction and determination of the residual deviation and the compilation of a deviation table for a given compass is carried out by a specialist-deviator at a deviation range specially equipped with leading signs. The deviation is considered destroyed quite satisfactorily if its value at all courses does not exceed ± 4 °.
As already mentioned, true headings and bearings must be plotted on the charts. To obtain true headings and bearings, you need to make a certain correction to the readings of the compass installed on the ship, since it shows the compass heading and compass bearings. The compass correction D K is the angle between the nordic part of the true meridian N I and the nordic part of the compass meridian N K. Compass correction D K is equal to the algebraic sum of the deviation s and declination d, i.e.:
D K = (± s) + (± d).
It follows that to obtain the true values, it is necessary to add the compass correction with its sign to the compass values:
IR = KK + (± D K)
or KK = IR - (± D K).
In fig. 43 shows the transition from MK to KK through declination.
In fig. 44 shows the relationship between all the quantities on which the correct determination of true sea headings depends. The angles formed by the lines N to, N m, N and and by the course and bearing lines are named as follows:
Compass heading KK - the angle between the line of the compass meridian N K and the heading line.
Compass bearing KP - the angle between the line of the compass meridian N K and the line of bearing.
Magnetic heading MK - the angle between the magnetic meridian N M and the heading line.
Magnetic bearing MP - the angle between the line of the magnetic meridian N M and the line of bearing.
True IR heading - the angle between the line of the true meridian N AND and the heading line.
The true bearing of the PI is the angle between the line of the true meridian and the line of bearing.
Deviation s - the angle between the line of the compass meridian N K and the line of the magnetic meridian N M.
Declination d is the angle between the line of the magnetic meridian N M and the line of the true meridian N I.
Compass correction D K - the angle between the line of the true meridian N And and the line of the compass meridian N K.
There is a mnemonic rule that helps the navigator to correctly operate the values of the true magnetic and compass directions. To fulfill this rule, you must remember the sequence: And K - d - MK - s - KK. If we algebraically subtract the declination d from the IR, then we get the MK value next to the right of the IR; if from MK we read algebraically the deviation s , then we get the KK value next to the right of the MC. If we algebraically subtract from the IC both those standing to the right of the IC. values d - declination and s - deviation, then we get CC. Provided that we have a compass heading and we need to get an MK, we make reverse actions: to the compass heading KK add the deviation s algebraically to the left of it and get the magnetic heading MC. If we algebraically add the declination d, which is to the left of the magnetic heading, to the magnetic heading, we get the true IR heading, and, finally, if we algebraically add the deviation s and the declination d, which are nothing more than the compass correction D K, to the compass heading, we get true heading - IR .
An amateur navigator, when calculating and working on a map, uses only the true values of headings, bearings and heading angles, and magnetic compasses give only their compass value, so he has to make calculations using the above formulas. The transition from known compass and magnetic values to unknown true values is called bearing correction. The transition from known true values to unknown compass and magnetic values is called bearing translation.
MILE MARINE
MILE MARINE
(Nautical mile) - the length of 1 \ "arc of the meridian, considering the Earth a ball, the volume of which is equal to the volume of the earth's ellipsoid. Then the value of a nautical mile is determined from the equality:
n= 2π R/ 360 60 = R· Arc 1 \ ",
moreover, according to the indicated condition, where - semi-major axis of the terrestrial spheroid, b- semi-minor axis.
If we take the values of these semiaxes according to the data of the Clarke spheroid, then n comes out equal to 1853.3 m = 6080.4 feet. But in the USSR, all maps are based on the data of the Bessel spheroid, therefore, by the circular of the Hydrographic Office No. 317 of 8 / VII 1931, the nautical mile was set at 1852.0 m, which corresponds to the length of 1 \ "arc of the elliptical meridian at latitude 45 °, that is, to the value:
(a + b)/2 arc1 \ "
according to the Bessel spheroid.
If 1 \ "arc of the elliptical meridian is taken as a unit for measuring distances, then the divisions of the vertical frames of the map will represent such a scale. This value changes with latitude from 1842.7 m= 6045.7 feet at the equator to 1861.3 m= 6106.7 feet at the poles. Difference 18.6 m, component of 1%, lies outside the accuracy of measuring the distances by the lag.
Our standard nautical mile is 1852.0 m = 6076.1 feet is used for graduation of the lag scale and for various calculations.
The British consider a nautical mile to be 6080 feet. and call her "Admiralty knot".
The length of 1 \ "of the earth's elliptical meridian, that is, the value that changes with latitude, they call" Nautical mile "or" Sea mile ".
In other countries, where other values are adopted for the semiaxes of the ellipsoid and b or where the radius of an imaginary globe, replacing the earth's ellipsoid, is determined not from a comparison of volumes, but by other methods, for example. by comparing the surfaces, there and for the nautical mile, values are obtained slightly different from 6080 feet, but close to them. The table below shows the nautical mile lengths adopted in various states.
States | Length of a nautical mile |
|
Germany | ||
Holland | ||
Portugal | ||
Samoilov K.I. Marine vocabulary... - M.-L .: State Naval Publishing House of the NKVMF of the USSR, 1941
Sea mile
a unit for measuring distances at sea, equal to the 1 'arc length of the earth's meridian. In different countries, the mile is defined at different latitudes, so it has different meanings. In Russia, the nautical mile is taken in latitude 44 ° 30 'and is 1852 m, in Great Britain and Japan - 1853.18 m, in the USA - 1853.24 m, in Italy - 1851.85 m.The international nautical mile is equal to 1852 m.
EdwART. Explanatory Naval Dictionary, 2010
Mile Sea
nautical unit of length used for measurements at sea, equal to 1852 m. The old Russian mile was equal to 7.468 m.
EdwART. Marine Dictionary, 2010
See what "MARINE MILE" is in other dictionaries:
MARINE MILE, a unit of measure for distance at sea. Defined as the length of one minute of the earth's arc. The international nautical mile is 1,852 m (6,076.04 feet), the UK nautical mile is 6,080 feet (1,853.18 m). Speed equal to 1 ... ... Scientific and technical encyclopedic dictionary
1 nautical mile equals 1852 m Glossary of Business Terms. Academic.ru. 2001 ... Business glossary
nautical mile- a unit for measuring distances at sea, equal to the arc length of the earth's meridian in 1. The international nautical mile is 1852 m ... Marine Biographical Dictionary
Sea mile- MARINE MILE, is equal to the length of one minute of the earth. meridiana. For the first time the size of the sea. M. b. It was installed in France in 1880, and for its calculation it was the length of 1/4 of the circumference of Paris. meridian, to paradise after a series of measurements b. defined in ... ... Military encyclopedia