Vessel's heading - the angle between the centerline of the ship and the direction to the north. Measured in degrees clockwise from 0° to 359°. Vessel's true heading (IR)- this is the angle between the northern part of the true meridian (NS line) and the center line of the ship (the direction of the bow of the ship). The true course is counted clockwise from 0 to 360°.
Magnetic course (MC)— the angle between the magnetic northern meridian N and the heading line.
The action 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 northern end of the magnetic compass needle points to the north magnetic pole of the earth N. Magnetic and geographic poles do not coincide. 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. Compass heading (CC) called the angle in the plane of the true horizon, measured from the north part of the compass meridian clockwise to the bow of the center plane of the ship. Compass courses and bearings can range from 0° to 360°.
Magnetic declination (d)— the angle between the northern part of the true meridian and the northern part of the magnetic meridian is called magnetic declination. Declination is measured from the northern part of the true meridian to the east or west from 0 to 180°. The eastern, or core, declination is assigned a plus sign, the western, or western, declination is assigned a minus sign. The magnetic declination for a given place is not constant; it constantly increases or decreases by a small constant amount. The magnitude of the declination in a given navigation area, its annual increase or decrease in the year to which the declination is given are indicated on navigation charts. Magnetic compass deviation (δ) is the horizontal angle by which the plane of the compass meridian deviates from the plane of the magnetic meridian (the difference between Nm and Nk). On each course, the deviation of ship compasses is different. This is explained by the fact that when the course changes, the position of the ship's iron relative to the magnetic compass needles changes. In addition, after the ship turns, the ship's iron is partially remagnetized, which also leads to a change in the ship's magnetic field.
Magnetic compass correction- the algebraic sum of deviation and magnetic declination, by the amount by which the compass directions differ from the true ones: ΔMK=δ+d MK deviation and declination must be taken with their own signs.

In order to find the true course (IR) knowing the magnetic course (MC) and the declination d of the compass in a given navigation area, it is necessary to algebraically add the declination given to the year of navigation with its sign to the magnetic course: IR=MK+(±d) hence: MK=IR-(±d)


Example:True heading(IR) = 90°Deviation (δ) = 5°E (deviation to the east (E) sign “+”, if to the west (W) sign “-“)Declination given to the year of navigation (d) = 10°W (we have a declination to the west, then the sign will be “-“, i.e. -10°)1) Find ΔMKΔMK=δ+d=5+(-10°)=-5°2) Find MKMK=IR-(±d)=90°-(-10°)=100°3)Find QCCC=IR-(±d)-(± δ )= 90°-(-10°)-(+5°)=95°
To make the calculations clearer, I’ll make a sketch, since the example is interesting:

It is also necessary to remember that: a) the course does not have negative values, if one is obtained during calculations, the result should be subtracted from 360°; b) if the course obtained in calculations is more than 360°, then 360° should be subtracted from the result.

The principle of determining the corrections of any compass ΔK is to compare the compass direction (measured using a compass) with the true direction:

ΔK = IR – KK; ΔK = IP – KP.

There are three main methods for determining compass correction:

-comparing bearings;

- along the target;

-by comparing compasses.

Determination of ΔK by comparison of bearings

The method is based on exact knowledge of the vessel’s location and the coordinates of the bearing being taken.

The true bearing is calculated, the landmark is taken bearing (CP).

The resulting CP is compared with the IP:

ΔK = IP – KP.

tgIP = Δλ cosφm/Δφ,

where: Δλ – difference in longitude between the ship and the landmark;

Δφ – latitude difference between the ship and the landmark;

φm = 0.5(φ1 + φ2) – average latitude.

IP can also be measured using a map, but this will add to the measurement errors using a spacer tool.

Determination of ΔK by site

A system of two or three beacons, signs, lights, located on the ground in a certain order, and forming a position line (alignment axis), is called a marine navigation alignment.

The gates are designed mainly to ensure navigation along straight sections (bends) of fairways in narrow areas where there are many navigational hazards.

According to their purpose, the alignments are leading, turning, secant and deviation

The method for determining compass corrections along a target is to compare the CP measured at the target marks at the moment of crossing the target line with the target PI indicated on the map:

ΔК = IPstv – KPstv.

To determine ΔK, you can also use the alignment of two natural landmarks shown on the map (mountain peaks, capes) or structures (chimneys, masts), the IP of which is measured on the map using a laying tool.

Determination of ΔK by comparison of compasses

The method is based on comparing the compass course, the correction of which is determined with the compass course, the correction of which is known. Based on the simultaneous comparison of rates, ΔK is calculated.

ΔK = Ko + ΔKo – K *,

where Ko is the compass course, the correction of which is known;

ΔKo – known correction;

K – compass course, the correction of which is determined.

The difference Ko – K = R is called comparison. From here

ΔК = R + Ko.

Example:

Determine ΔMK if KKmk + 6º, GKK = 354º, ΔGK = -2º.

Solution:

R = Ko – K = GKK – KKmk = 354º - 366º = -12º;

ΔK = R + Ko;

ΔMK = R + ΔGK = (-12) + (-2) = -14º.

Answer: ΔMK = -14º.

Derivation of formula *:

IR = K + ΔK; IR = Ko + ΔKo; because IR = IR, then

K + ΔK = Ko + ΔKo; ΔK = Ko + ΔKo – K.

Determining the gyrocompass correction

In order to reduce random errors, after the gyrocompass arrives at the meridian (while parked), multiple bearing measurements are taken every 10 - 15 minutes for 2.5 - 3.0 hours. Based on the measurement results, the average value of the gyrocompass bearing of the GCP is calculated:

GKPsr = 1/p(GKP1+GKP2+GKP3+…+GKPp);

where n is the number of measurements.

Then the constant correction is determined:

ΔGK = IP – GKPsr.

At sea, the constant correction of the gyrocompass is determined when the vessel moves uniformly. At the time of each compass bearing measurement, a high-precision observation is performed, relative to which the true bearing is calculated. For each gyrocompass bearing, the corresponding IP and the gyrocompass correction ΔGK are calculated. The average correction value is calculated using the formula

ΔGKsr = 1/p(ΔGK1+ΔGK2+ΔGK3+…+ΔGKp);

where n is the number of measurements.

Determination of magnetic correction

compass

The magnetic compass correction depends on the magnetic declination d and the deviation δ:

ΔMK = d + δ.

Declination changes with changes in the ship's coordinates and over time, deviation depends on the ship's course.

Therefore, ΔMC, determined by comparing bearings, by alignment and by comparison, can only be used on the course on which it was determined.

In the general case, the magnetic compass correction is defined as the algebraic sum of the magnetic declination d, which is taken from the navigation chart and reduced to the year of navigation and deviation δ, selected from the deviation table.

Sometimes, when interviewing 3rd mates, I jokingly ask: “How does the morning begin for the 3rd mate and for the captain?”

The young guys are confused and try to come up with something to answer my unexpected question.

I explain to them all that the captain’s morning begins with a cup of aromatic coffee, and for the 3rd mate, the morning begins with adjusting the compass. A joke of course, but with a grain of truth. This is what I want to talk about.

All navigators know that the compass correction must be determined every watch. How to do it?

In coastal navigation, when there are coastal landmarks, this is very simple and takes a few minutes. What to do if the ship is on the open ocean? There is nothing around, only the sky, the ocean, seagulls and the captain, who is watching with interest how the 3rd mate will solve the task. He probably considers you “GPS generation”. As they say, everything ingenious is simple.

There is a quick and easy way to determine the compass correction based on the lower or upper edge of the Sun. To do this, you need very little - install a direction finder on board where the Sun sets, and at the moment when the last segment disappears behind the horizon. After this, you should take a bearing, note the time, latitude, longitude and enter the data into the Navimate or Skymate computer program. If you don’t want to blush in front of the captain, or at some inspection, then show your class and calculate the correction manually.

For this we need a manual called Nautical Almanac.

So, we take a bearing on the Sun, record the current time and coordinates, record the course using the gyro and magnetic compass.

Example:

Date: 03/19/2013 LMT(UTC+2): 17:46:30 Lat: 35-12.3 N Long: 35-55.0 E

Gyro bearing: 270.6 Heading 005 Magnetic heading 000

We adjust the time to Greenwich (2nd time zone) GMT 15:46:30

Finding GHA (Greenwich Hour Angle)

Finding DEC (declension)

To find them, go to the main table of the Almanac and find the current date. We write out GHA and DEC for the current hour, and also write out the correction d for the Sun (bottom right of the table). In our case it is equal to 1.0.

Then you need to correct the Greenwich hour angle and declination by adjustments to minutes and seconds.

This data can be found at the end of the book. The pages are headed by minutes and a GHA correction is provided for each second. There is also a correction for declination on the right side, which is selected according to d.

M’S” = 11-37.5 corr = 0-00.8

Now we adjust the Greenwich hour angle to the local time zone. To do this, we add (if E) or subtract (if W) our longitude:

GHA = 54-42.5 + Long 35-55.0

LHA = 90-37.5

Go to the Sight reduction table and select the values ​​A, B, Z1:

A = 55.0 B = 0 Z1 = 0

For the second entry in the table we need F and A.

To get F you just add B and DEC (+/-).

Our DEC is positive if the sign of declination and latitude coincides (N and N/S and S).

If our declination and latitude are different, then DEC is negative.

B=0

DEC=0-20.6S

F = 359 39.4 (rounded to 360)

Now having F and A, we enter the same table for the second and last time, and write out the second component of the azimuth Z2:

Z2 = 90

Then we add Z1 and Z2 and get the semicircular azimuth Z:

Z = 0 + 90 = 90

We convert semicircular azimuth to circular using the rule:

For northern latitude, if LHA is greater than 180: Zn = Z, if LHA is less than 180: Zn = 360 Z

For Southern latitude, if LHA is greater than 180: Zn = 180 – Z, if LHA is less than 180: Zn = 180 + Z

In our case Zn = 360 – 90 = 270

The desired bearing has been found. We take away our compass bearing 270 – 270.6 = - 0.6W

In order not to get confused in the order of calculations, I present the algorithm:

1. We make calculations, record bearing, position, time, and course.
2. We convert local time to Greenwich Mean Time.
3. We select the value of LHA and Dec from the tables.
4. We correct them by adjusting them for minutes and seconds.
5. Select the values ​​A, B, Z1 from the table.
6. We calculate F and select Z2 from the table.
7. We find the azimuth and convert it to circular.
8. We find the compass correction (true bearing minus compass bearing).
9. WE HANG A LARGE ASTRONOMICAL MEDAL ON OUR CHEST.

At first glance, everything looks cumbersome and unclear. But after a couple of practical calculations, everything will fall into place.

By the way, by adjusting your compass as the sun sets, you will have a unique chance to see the green beam. The fact is that at sunset, at the moment when the Sun disappears behind the horizon, due to refraction and refraction of color, it is very rare, but you can observe a green ray for several seconds. This mysterious, enigmatic and very rare phenomenon is reflected in numerous legends of different peoples, and is overgrown with legends and predictions.

For example, according to one legend, the one who saw the green ray will receive a promotion, prosperity, and will be able to meet the one with whom he will meet his happiness.

And this is not a story, since the Captain, having seen and appreciated the efforts, as well as the competence of the young navigator, will, of course, recommend him for promotion.

So determining the compass correction based on sunset is a direct path to promotion and, as a result, to well-being and happiness.

I wish all young navigators calm seas, career advancement, and a return to their native shores. May the green ray bring you happiness in your life.

After I started working under contracts, quite often I came across some methods that were accepted all over the world, but were completely different from the methods of the former Union. One such technique is determining the compass correction. Knowing the compass correction is both an international requirement and often a company requirement, and, just as no nation can lay claim to genius, no nation is immune from stupidity. I was in a company where it was necessary to determine compass correction every watch, and if this could not be done, then there should have been a mandatory entry in the log about the reason for the failure.

No one argues that the most effective method for determining compass corrections is by alignment. But what to do on the high seas? In fact, only astronomical methods remain.

The idea of ​​somehow improving the process of determining the compass correction was prompted by my third, who regularly came to my watch and was engaged in taking bearings of sunrise and sunset. After that, he spent about half an hour toiling over some wild calculations. I had to look for a ship in the nearest port on which the forgotten MT-75 tables would be preserved. I made photocopies of the necessary pages and explained how to use them to the Filipino, who was our third navigator. His gratitude knew no bounds.

Maybe someone remembers, in MT-75, each table contains explanations with formulas by which this table was calculated. Therefore, the second stage of my activity in this direction was the translation of the table for determining compass corrections into electronic form, namely into EXCEL. Still, it’s easier to carry one laptop to a contract, rather than a bunch of paper. After arriving on the ship, I printed out these tables and then used the paper copy.

But various routine actions remained, which increased the calculation time. For example, when making calculations, degrees and fractions are used to enter the table, rather than degrees and minutes. It would seem that it would be easier to divide the minutes by 60 - you get fractions of a degree. But all this is again an unnecessary action, which means extra wasted time. A more complex stage is interpolation between neighboring table values, which takes much longer and significantly increases the likelihood of making an error. Why do all this if EXCEL spreadsheets do it all for you? Therefore, the second stage of my automation was programming all these routine actions.

A third stage of automation is also possible - this is when the declination of the Sun will be automatically calculated. But this stage is too complex to implement in practice, and it is not at all necessary, because On any ship you can easily find a Naval Astronomical Yearbook (MAE), because its presence on board the ship is also an international requirement. It can be either an independent publication or part of some other book. For example, MAE is included in Brown's Almanac.

So, if you are interested in this technique, then the calculation procedure is as follows:

Take the bearing of the upper edge of the sun at the time of sunset/sunrise

Record the given bearing, latitude and time

Convert time to Greenwich and use it to determine the declination of the Sun from MAE

Enter the required data into the spreadsheet and get the result

For example, this whole calculation takes me less than a minute. You just need to remember that the MT-75 tables were calculated for predefined values, i.e. standard refraction, horizon visibility range, etc., but in most cases the calculation error does not exceed 0.1 degrees, which is much less than the error in taking bearings. And who needs special precision? The main thing is that if you use this method regularly and get approximately the same compass correction and suddenly get some incredible value, then there are quite a few options. Either you entered the wrong data, or something happened to nature, or your compass is about to close.

§ 17. Magnetic and compass points, courses and bearings. General compass correction

Rice. 21.

Thus, Magnetic course The vessel is called the angle at the center of the compass, measured from the northern part of the magnetic meridian to the direction of the bow of the ship's center plane clockwise from 0 to 360°. Compass heading- the angle at the center of the compass, measured from the northern part of the compass meridian to the direction of the bow of the centerline plane of the ship clockwise from 0 to 360°. Magnetic bearing an object is called the angle at the center of the compass, measured from the northern part of the magnetic meridian to the direction towards the object clockwise from 0 to 360°. Compass bearing an object is called the angle at the center of the compass, measured from the northern part of the compass meridian to the direction towards the object clockwise from 0 to 360°.

True courses and bearings are related to the magnetic following algebraic relations:

Solution(formulas 19)

Solution(formulas 20)

Solution(formulas 21)

Solution(formulas 22)

The general correction is called the truss or leading and is given a “plus” or “minus” sign depending on whether the northern part of the compass meridian is deviated towards the truss or the leading from the northern part of the true meridian. For example:

AK = +3° or AK = -10°.

The general compass correction, declination and deviation are related by the following algebraic relationships.