Where is the main magnetic compass installed on the ship? Magnetic compass: history of creation, principle of operation and application. Ruler on a magnetic compass
A magnetic compass is the simplest of all types of compasses known today. But it continues to be used by many people: tourists, military, fishermen, etc.
The simplest models of magnetic compass consist of:
- Arrows are the main element of any such device
- Scales indicating the cardinal directions
- A housing in which the pointer is fixed so as to be able to rotate
- Protective glass that protects the needle and scale from mechanical damage
More complex models can be equipped with additional elements, such as:
- Movable dial with pointer for faster and more convenient operation
- Arrest for fixing the arrow
- Fluid for quick needle stabilization
- Rear sight and front sight allowing for more accurate measurements
- Mirror for monitoring the position of the compass needle during field measurements
- Rectangular base with ruler for measuring on a map
- A clinometer that allows you to determine the slope of the terrain
- Lens for working with small map details
- Fastening elements for more comfortable work with the compass
- Protective housing that protects the flask from damage
Now let's look at some of the listed elements in more detail.
compass needle
The needle is the main element of any magnetic compass, although there are models in which the needle forms one whole with a disk on which a scale is applied.The compass needle is made of ferromagnetic material and is a permanent magnet that rotates on an axis. This arrow is directed towards the magnetic poles of the Earth, unless it is significantly influenced by extraneous magnetic fields (here are some options)
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Most often it is located on the spire to reduce friction during rotation. In some models of compasses, it is integral with the disk on which the scale is applied.
Like any other magnet, the needle of a magnetic compass has a north and south pole, which are located at its two opposite ends. The northern one points towards the north, the southern one - towards the south.
To avoid confusion during measurements, the opposite ends of the arrow must be different in some way. To do this, they are most often painted in different colors, or only the northern end of the arrow is painted.
How to distinguish the north needle of a magnetic compass
The simplest option is a compass needle with a triangular or other arrow shape in the north or a dot (usually a luminous one).
Quite often, the arrow is painted in different colors, or only the northern end of the arrow is painted. The color of the north arrow may vary. This is decided by the manufacturer, and often does not coincide with what is written in various sources.
Usually one end of the arrow is marked with color. It could be blue, red, orange, green etc. Regardless of the color, if only one end of the arrow is marked, then it is the northern one. In this case white or black paint on the arrow are background colors.
If a compass has red and blue arrows, then the red compass arrow pointed south and the blue arrow pointed north. Blue was associated with cold, and red with warmth.
Therefore, before using the compass, it is necessary to independently check your compass by finding your way around the area in any available way (for example, using a map, stars or the Sun) and comparing the result with the readings of the device.
Magnetic compass card
If you look at the examples of compasses above, you will see that they have letters and numbers printed in a circle on a disk located near or under the arrow. They are called a card or sometimes some call it scales.
First of all, they are indicated on the card. There are 32 in total, dividing the compass disk into 32 equal parts, but most often only 8 are used: 4 main and 4 auxiliary:
- N (North) - north.
- NE (North-East) - northeast.
- E (East) - east.
- SE (South-East) - southeast.
- S (South) - south.
- SW (South-West) - southwest.
- W (West) - west.
- NW (North-West) - northwest.
Also on the compass scale there are numbers that, depending on the compass model, show or degrees or thousandths. Although there are models with two scales at the same time.
Degrees are used by tourists to work with azimuths, and thousandths are units of measurement of angles used in military affairs.
If this is a degree scale, then the numbers in it are arranged in ascending clockwise order. A full rotation is 360 degrees.
If the scale is given in thousandths, then the numbers here can be located either clockwise or counterclockwise, depending on the compass model.
The values of the scale showing thousandths can lie within different limits. There are three possible options:
- from 0 to 60
- from 0 to 63
- from 0 to 64
- in the former USSR and some other armies, the thousandth was taken equal to 1/6000
- in the Swedish army - 1/6300
- in the NATO army - 1/6400
To find out the price of a scale division, you need to take the adjacent serifs on which the numbers are indicated and divide their difference by the number of segments separated by the serifs between these numbers.
For example, in order to find out the division value of the internal scale of the Adrianov compass:
- Let's take offhand two of its values, lying next to each other on the scale - 45° and 60°.
- We determine the difference between them: 60° – 45° = 15°.
- We count the number of spaces delimited by strokes between the values of 45° and 60° - there are 5 of them.
- We calculate the price of dividing the degree (internal) scale of this model: 15° / 5 = 3°.
Magnetic compass housing
The compass body can be either metal or plastic.Metal cases are generally stronger. There are even special impact-resistant models that can withstand significant mechanical impacts. However, at the same time, compasses with a metal frame are usually heavier compared to models whose body is made of plastic.
It is believed that the brass case contributes to faster stabilization of the arrow due to the resulting induction currents. But in most modern models of tourist compasses and compasses for orienteering, this problem is solved in a different way - by filling the sealed flask of the device with a special liquid, which creates additional resistance for the needle and instantly dampens any of its vibrations, which is very convenient, especially if you have to orient yourself on the go.
Movable magnetic compass dial
A movable dial with a pointer makes working with the compass faster and more convenient.
On the compass dial, divisions go from 0° to 360° in a counterclockwise direction or thousandths.
The arrester presses the needle to the top glass of the bulb and thus prevents it from moving, which is especially important when a person moves over rough terrain, when the fluctuations of the compass needle can be significant.
One of the most famous compasses with a arrester is the Hadrianov compass. In this model, the arrow is fixed in a stationary position when the lock is pressed and is set in motion if the lock lever is slightly pulled out of the body.
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Rear sight and front sight (sight)
The rear sight and front sight (sight) make it possible to accurately determine the azimuth to a selected object or to find the direction on the ground using a known azimuth.The rear sight and front sight, as a rule, are located on opposite sides of the point where the compass needle is attached, and even when rotated, they retain their position relative to the center of the needle. Although, of course, not all models provide for the mobility of these elements.
There are different options for the design of rear sights and front sights.
Mirror
A mirror as part of the compass design usually serves for more accurate measurements, since it allows you to monitor the position of the arrow while the device is sighting an object located on the ground.In some models, the mirror also allows you to more accurately point the compass at the desired object.
Typically, such a mirror is a flat, smooth metal plate, which makes it invulnerable to falls, because, unlike a glass mirror, the metal plate will never break.
In addition to more accurate measurements, the mirror on the compass allows you to use the mirror for its intended purpose, for example, to independently remove a foreign body (midge, speck) that has entered the eye. And in an emergency, such a mirror can reflect the sun's rays and send distress signals.
Fluid for quick needle stabilization
This non-freezing liquid slows down the movement of the compass needle and stops it faster than in a case filled with air.
At high altitudes or low temperatures, the liquid may shrink and form bubbles. Bubbles do not affect accuracy. They disappear when the compass returns to normal conditions.
Substrate
The backing is a rectangular transparent base on which the compass is placed.
Typically, ruler markings are applied to the substrate, which allows it to be used effectively for working with the map.
Very often, instead of one ruler, two scales are applied to the tablet, one of which is designed in such a way as to measure distances in inches or to automatically convert map centimeters to kilometers on the ground. The second option only works on maps of a certain scale, which is indicated on the ruler with such a scale.
If the substrate is transparent, then additional scales can be applied to it.
Also, cutouts in the form of various geometric shapes of different sizes can be made on the substrate for sketching symbols on the map, and a lens can also be built into it for viewing small details of the area plan/map.
Magnetic compass mount
There are three main options for attaching a compass: on the thumb, on the wrist, or hanging on the neck.
This type of compass mount is used for orienteering. It allows you to quickly navigate to the cardinal directions without additional manipulations.
However, finger-mounted devices are less accurate than others for two reasons:
- their dimensions are too small to be marked with a scale with a minimum division value
- there is no ruler in their design, which makes it impossible to make accurate measurements on the map
Typically, such compasses are more accurate when taking measurements on the ground, since they have a more “detailed” scale, and are often equipped with sighting elements.
Attaching a magnetic compass by hanging it on your neck
To hang the compass around your neck, many models are equipped with a thin rope.When moving, the compass is hidden under outer clothing so as not to dangle around the neck, not to cling to surrounding objects (for example, tree branches, protruding parts of the relief) and not to hit them, and if necessary, it is quickly removed and used for its intended purpose, and then again hides under clothes
Luminous scale and pointer
Often a compound is applied to the pointer and scale that glows in the dark. Which, of course, improves the ability to navigate in the dark.
Initially, for the luminous compass, special phosphorus substances were applied to the magnetic needle and dial, which have the property of phosphorescence - glowing in the dark after being irradiated (“charging”) with sunlight. However, the duration of this glow was short.
In the 20s last century, substances (usually based on thorium or radium isotopes) began to be used for these purposes, the glow of which was due to soft and hard radiation (radioluminescence). At the same time, “recharging” with sunlight was not required, and the glow persisted for decades. However, due to the harmful effects on health, in the middle of the last century they were replaced by new types of phosphorescent materials, the glow duration exceeded 10 hours.
In the 1960s The Swiss company Mb-microtec AG has developed a new technology for radioluminescent illumination GTLS (Gaseous Tritium Light Source - gas tritium light sources), which received the trade designation Trigalight. The technology is based on tiny cone tubes filled with tritium (an isotope of hydrogen). Their inner surface was coated with a phosphor that glowed under the influence of soft tritium radiation. Since the chemical element tritium is designated 3H, this technology is sometimes called “3H” or “H3” backlighting.
Depending on the composition of the phosphor, the glow of tritium tubes can be of different colors - from green and yellow to blue and red. Military compasses usually use phosphors that produce a green color (the brightest and most intense glow).
The guaranteed service life of tritium backlight is at least 10 years (depending on the composition of the phosphor and manufacturing technology, the glow can last for 15–20 years).
The safety of compasses with tritium illumination is confirmed by modern medical research, which has established that the annual dose of trigalight radiation is almost 500 times less than that from natural background radiation.
Despite many advantages, tritium illumination technology also has a significant drawback - the high labor intensity of manufacturing trigalight tubes and, as a consequence, the high cost of products using this technology.
Commonly used in geological and some military compasses.
Ruler on a magnetic compass
If you carefully examined the above compasses, you quite often saw a ruler on them.
A ruler is needed to plot a route and measure distances on a map.
- Marine stations
- River stations
- Others
Marine radio equipment is equipment designed to protect human life at sea, ensure the safety of navigation, control the operation of the fleet and transmit public and private correspondence. To effectively use radio equipment on ships, you need to know its construction principles, technical characteristics and operating features. Depending on the navigation area, different requirements are put forward for marine radio equipment.
A1 – in the coverage area of coastal VHF radiotelephone stations using DSC.
A2 – in the coverage area of MF radiotelephone stations using DSC, excluding area A1.
A3 – within the range of INMARSAT satellites, excluding areas A1 and A2.
A4 – outside the areas A1, A2, A3.
Thus, the radio equipment on the ship consists of three complexes: VHF equipment, MF/HF equipment and a ship earth station (SES) of the INMARSAT system. Regardless of the navigation areas, each vessel must be equipped with: a VHF radio installation, a radar beacon (radar transponder), a NAVTEX receiver, an EPIRB (emergency radio buoy), and portable emergency VHF radios.
The radio equipment on the ship must meet the GMDSS requirements specified in the rules of the RMRS (Russian Maritime Register of Shipping) and RRR (Russian River Register). Each ship must be equipped with a reserve power source to enable radio equipment to provide distress communications in the event of failure or damage to the main and emergency power sources. When moving from one power source to another, light and sound alarms should sound. To operate and repair the equipment, maintenance is provided, which carries out the following procedures: delivery to the installation site, storage (if necessary) and installation. All these steps must be carried out in accordance with the instructions in the technical documentation.
The quality of radio equipment is a set of indicators that determine its compliance with modern requirements of science and technology. Device quality indicators include reliability, performance characteristics, efficiency, safety, design, etc. Many indicators have a numerical value and, in essence, determine the effectiveness of the use of any equipment on the ship.
On ships with a displacement of over 500 r.t. there must be at least three VHF portable stations and two radar transponders. On ships with a displacement from 300 to 500 r.t. - two stations and 1 radar. It is also recommended to equip ships with equipment for receiving facsimiles.
In the company's product catalog you can familiarize yourself with various models and brands of global radio equipment manufacturers and make the necessary order.
- Gyroscopic compasses
- Magnetic compasses
- Chartplotters
- Lags
- Weather sensors
- GNSS GPS/GLONASS receivers
- Radar stations
- Repeaters
- SKDVP (BNWAS)
- Voyage data recorders VDR/U-VDR
- Automatic Identification System (AIS)
- Systems for receiving external audio signals
- Sonars
- Satellite compass
- Echo sounders
- Autopilots
- Electronic cartography
- FleetBroadband
- Inmarsat LRIT, SSAS (OSDR, SSOO)
- Iridium (Iridium)
- Satellite television
- BGAN terminals
- VSAT terminals
Satellite communications at sea are now an important means of communication with the shore. Satellites of various operators create a large coverage of the earth's surface, which ensures communication from anywhere in the world.
On ships supervised by classification communities, satellite equipment is used both as mandatory installation and as additional equipment. On small ships, boats, yachts, satellite equipment is used at the discretion of the owners and mainly for accessing the Internet.
Equipment types:
Inmarsat LRIT, SSAS terminals (OSDR, SSOO) are marine satellite equipment required for installation on passenger, commercial and cargo ships with navigation areas A2, A3, A4.
- Ship Security Alert System - allows you to send a hidden alarm signal in the event of an attack on the ship. LRIT or LRIT is a long-range vessel identification and tracking system.
- FleetBroadband terminals are equipment for a marine satellite communication system that provide broadband Internet access, satellite telephone communications, and SMS messaging.
- VSAT – equipment that provides high-speed data transmission via satellite Internet, which even allows you to organize video conferences on board.
Also for these purposes, BGAN terminals are used, which differ from FBB and VSAT equipment in their compactness, mobility and communication speed.
Among highly specialized satellite marine equipment, the following vessels are used: a satellite communication station, an antenna for receiving a TV signal and, for long-distance navigation areas, telephones operating through satellite communication systems of operators such as Iridium, Inmarsat and Thuraya.
- Inclinometers
- NAVIS automation systems
- Praxis automation systems
- Automation systems MRS
- Fuel consumption control systems
- Sensors
- ABS automation systems
- Valkom automation systems
1. Maintenance, service and repair of ship electrical automation:
- automation of remote control systems for main engines;
- automation of ship power plants;
- repair and adjustment of power plant systems;
- repair, adjustment and testing of automation and alarm systems of main engines (Wartsila, MAN, MAK, SKL);
- repair, adjustment and testing of automation and alarm systems of auxiliary and emergency diesel generators (Volvo Penta, Scania, Deutz, CAT).
2. Maintenance, service and repair of electrical equipment of general ship systems:
- repair, adjustment of steering devices and automatic pilots;
- repair, adjustment, comprehensive testing of fire alarm systems;
- automation of boiler equipment;
- automation of fuel preparation systems;
- automation of water treatment systems;
- automation of wastewater treatment systems.
3. Maintenance, service and repair of electrical equipment of deck mechanisms.
4. Development and coordination of design documentation for the modernization and re-equipment of ship automation systems.
5. Major, medium and current repairs of electric motors and generators of any power. Repair and adjustment of the generator excitation system, adjustment of parallel operation of generators.
- Headsets and handsets
- Hydrostats
- Spare parts for KVU
- Spare parts for gyrocompasses
- Spare parts for typhons
- Magnetrons
- Converters and distributors
- Batteryless communication systems
- Fire safety systems
- Marine displays and PCs
- Ship typhons
- Batteries (battery)
- Power supplies
- Additional blocks
The technical means used to determine the main directions at sea also include magnetic compasses. Magnetic compasses use the property of a magnetized needle to be located along the magnetic lines of force of the Earth's magnetic field in the north-south direction. On a ship, the magnetic needle, in addition to the Earth's magnetic field, is affected by magnetic fields created by the ship's iron and electrical installations. Therefore, the magnetic needle of a compass installed on a ship will be located in the so-called compass meridian.
Simplicity of the device, autonomy, constant readiness for action and small size are the advantages of a magnetic compass compared to a gyroscopic one.
But the readings of the magnetic compass must be corrected by a correction, the magnitude and sign of which vary depending on the course of the ship, its location on the earth’s surface and other reasons. At high latitudes, the accuracy of the magnetic compass readings decreases, and in the area of the Earth’s magnetic and geographic poles it ceases to function at all.
All naval vessels are equipped with marine magnetic 127 mm (5 inch) compasses (Fig. 131).
The main parts of the compass are: bowl 1 with a card, binnacle 2, direction finder 3 and deviation device 4.
Bowler(Fig. 132) is a brass cylindrical tank divided into two chambers that communicate with each other. The upper chamber 1 houses the compass card, the lower chamber 2 serves to compensate for changes in the volume of the compass fluid when the ambient temperature fluctuates.
A solution of ethyl alcohol (43% by volume) in distilled water, which freezes at a temperature of -26°C, is used as a compass liquid. To reduce the vibrations of the pot during pitching, a brass cup with a lead weight 3 is attached to the lower part of its body.
The bowler is equipped with a cardan ring, which allows you to keep the azimuth ring of the bowler in a horizontal position.
Cartushka(Fig. 133) - the main part of the compass, consists of a system of magnetic needles 1, a float 2, an agate firebox 3, a screw for fastening the firebox 4, six brackets 6 supporting a mica disk 5, onto which a paper disk is glued, divided into rhumbs and degrees .
Rice. 131.
Rice. 132.
Direction finder- a special device for determining directions to visible objects and celestial bodies. It consists of a base, object and eye targets and a deflector cup.
Binnacle made from silumin. The main parts of the binnacle are: body, upper and lower bases, shock-absorbing suspension, deviation device and protective cap.
Rice. 133.
Deviation device is placed inside the binnacle and is a brass pipe with two movable carriages for installing destroyer magnets. A set of magnets for eliminating semicircular deviation is supplied in a special wooden case.
All manufactured 127 mm compasses have a bottom illuminated card. The lighting system includes: a umformer, a power supply and a socket with a light bulb (if powered from the ship's DC network).
The lighting system can operate on ship's alternating current, but in this case, instead of an umformer, a transformer is included in the power circuit, reducing the voltage to 6.12 or 24 V.
A compass is a navigation device designed to determine the course of a ship and directions to various coastal or floating objects that are in the field of view of the navigator. The compass is also used to determine the direction of the wind and the drift of the ship. Based on the readings of the magnetic compass, the ship is controlled, and with its help, bearings are determined to coastal objects. Typically, a magnetic compass is installed in a high, open place in the centerline of the ship.
The magnetic compass uses the property of a magnetic needle to set its ends in the direction of the magnetic field acting on it. In addition to the earth's magnetic field, the ship's compass needle is also affected by the magnetic field created on the ship by the iron hull and iron pieces of equipment. Under the influence of these two forces, the magnetic needle is established in the plane of the compass meridian. A magnetic compass is also subject to the influence of other external forces that arise when the ship rolls and turns, which remove the needle from a stable position. The compass needle is also affected by the vibration of the housing from engine operation.
In marine magnetic compasses, the role of the needle is played by a system of four, six or more thin magnets placed in a pot of liquid, which quickly damps the vibrations of the magnetic system.
For compasses used on land, including tourist ones, a scale with degree division is printed on the compass body. Such a compass, installed on a ship, will rotate with the ship and the reference scale. - WHAT IS THIS ALL FOR??????????????????????????
An air float keeps the magnetic system afloat, which ensures minimal friction at the suspension point. A marine magnetic compass is equipped with a special device - a deviation device, which reduces the impact on the magnetic system of the compass of the magnetic field of the iron hull of the ship. With the help of a gimbal suspension, the horizontal position of the pot is ensured during pitching, roll and trim. NO BASIC FORMULA
3.2. Methods for determining compass correction. MEANING GYROCOMPASS
A compass correction is the value of a parameter (course or bearing) that compensates for the systematic error in its measurement.
To determine the correction of any compass, it is necessary to compare the true and compass directions to the same landmark, i.e.:
∆MK = IP – CP.
Determination of compass correction along the target. The target IP is removed from the map. The control point is taken at the moment of crossing the alignment line. Determination of compass correction along natural coastal alignments (for example, sections of two capes). At the moment of crossing the line of natural alignments, the compass bearing is taken and compared with the direction of the line taken from the map passing through the sections of the two capes.
Determining the compass correction based on the bearing of a distant landmark. This method is used when the vessel is anchored, when the landmark and anchorage location is precisely known.
Determining the compass correction by comparison with another compass whose correction is known. The method is used to determine the correction of the main and traveling magnetic compasses by comparing the readings with a gyrocompass, the correction of which is known. On command, two observers simultaneously note the heading on both compasses. Define:
∆MK = (GKK + ∆GK) – KK.
Determination of the compass correction when determining the ship's position using three bearings. When determining the position of a ship using three bearings, a so-called triangle of errors may appear, i.e., the laid position lines do not intersect at one point. When there is confidence in the correct identification of landmarks and in the absence of gross errors in bearings, and the triangle turns out to be large, this indicates an error in the adopted compass correction. To eliminate such an error, and at the same time determine the current compass correction, proceed
in the following way:
– all bearings are changed by 3-5 0 in one direction or another, and after laying a new triangle of errors is obtained;
– lines are drawn through the similar vertices of the old and new error triangles, and the point M of their intersection is taken as an observed place on the vessel, free from the influence of a systematic error in the compass correction ∆K;
– point M is connected to landmarks on the map and the resulting true bearings are measured with a protractor. By comparing them with the compass bearings of the same landmarks, three values of the compass correction are found ∆K = IP - KP. The arithmetic mean of the results obtained is taken as the actual correction for a given course.
When determining the compass correction astronomically, the bearing to the luminary, measured using a direction finder, is used as the compass direction, and the calculable azimuth of the luminary, calculated at the time of measurement in a tabular or machine way, is used as the true direction.
The following conditions must be met:
1. To clarify ∆K, use luminaries located at a low altitude (h< 30°) и вблизи диаметральной плоскости судна (КУ< 30°);
2. Measurements should be made in series of 3-5 bearings with re-fixation of the direction finder;
3. The bearing is measured with an accuracy of 0.1°, the measurement moments are recorded with an accuracy of no worse than 2-3 s;
4. The countable azimuth must be converted into a circular count, i.e. IP = A k.
There are several ways to determine AK by luminaries:
1. Determination of ∆K from a star located at an arbitrary azimuth;
2. Determination of ∆K from the Sun at the moment of its true rising and setting;
3. Determination of ∆K from observations of the North Star.
The first method is the main and most common, the other two are its special cases. It is performed in the following sequence:
Example: August 24, 2006, Mediterranean Sea. V T s = 20:46′; N=1E; Measured a series of compass bearings: α Scorpio
– KP av = 219.5°; T gr.av. = 19:45′ 07″, ϕ с = 33°19.0′ N; λ c = 21°43.0′ E; KK = 196.0°, determine ∆K.
1. Calculate from MAE δ and t m of the star α Scorpius on T gr.av. =19: 45′ 07″
2. Calculate the true bearing of the star in one of the following ways: – using TVA tables:
Using a calculator using PT formulas: SHIPMENTS WILL NOT UNDERSTAND
Ctg A = cosϕ · tgδ · cosec tм - sinϕ · ctg tм
Сtg A = 0.8356∗ - 0.4975 ∗ 1.4525 – 0.5493 1.0547 = -1.1825
A = arcctg – 1.1825 = 40.22°; A k = 220.2°
on a computer using the “Electronic Almanac” program А к = 220.2°
3. Calculate the compass correction:
∆K = IP – CP = 220.2° - 219.5° = + 0.7°. – the symbols in the formulas are NOT CLEAR
Determination of ∆K by the Sun at the time of its rising and setting:
If at the moment of sunrise or sunset (at the moment the horizon touches its lower edge) you measure its compass bearing, then you can quickly and fairly accurately determine the compass correction. The specificity of this method is that at the moment of sunrise (sunset) the height of its center is equal to a very specific value (- 24.4′ cm. MT-2000), therefore the desired Azimuth is a function of two parameters - latitude and declination. Therefore, A c is easier to calculate and easier to tabulate. To calculate the azimuth of the Sun, table 3.37 MT-2000 is used. The input arguments in Table 3.37 are the countable latitude - ϕ с, taken from the pad at the time of measuring the compass bearing, and the declination of the Sun - δ о, which is selected from the MAE at the Greenwich moment of sunrise (sunset). The tabulated azimuth is given in semi-circular count; The first letter of the name is the same as the number latitude, and the second letter at sunrise is E, and at sunset it is W.
It should be remembered that the instantaneous compass correction obtained in this way is less accurate and reliable than that obtained by the main method, so it is often used only for control.
Example: April 12, 2006; Black Sea. ϕ с = 44°25.0′ N; λ c = 34°12.0′ E; CC = 92.0°; T s = 06:08′; N=3E; We measured the compass bearing of the Sun at the moment of its rise: KPo = 77.2°; determine ∆K.
1. Determine the Greenwich time of sunrise and at the obtained moment select the declination of the Sun from MAE:
T gr = T s ± N W/E = 06:08′ – 3 = 03: 08′
At T gr = 03:08′ 04/12/02 from MAE - δ o = 08°36.0′ N
2. Included in the table. 3.37 MT-2000 with ϕ с = 44°25.0′ N and δ о = 08°36.0′ N and obtain on April 12 А t = N 77.7° E, taking into account
interpolation by ϕ and δ o results in A k = IP = 77.5°.
3. Calculate ∆K = IP – CP = 77.5° - 77.2° = + 0.3°. THE SAME THING – IT’S UNCLEAR WHAT’S WHAT’S WHAT
3.3. Practical methods for determining the deviation of a magnetic compass.
Typically, residual deviation is determined after its destruction, but sometimes the determination of deviation can be performed as an independent work. Such a need arises if a noticeable discrepancy between the observed deviation on individual courses and its tabulated values is detected, as well as when transporting metal cargo, after sailing in ice, or when the ship’s latitude changes significantly.
There is a full definition of deviation for compiling a deviation table and a partial one, on individual courses, in order to monitor the operation of the magnetic compass.
To compile a table, deviation is most often determined at eight main and quarter compass courses, then, using the observed deviation values, deviation coefficients A, B, C, D and E are calculated. Next, using the known coefficients, a deviation table is calculated for any number of courses, using formula (1) . Depending on the value of the coefficients, the deviation table is calculated for 24 or 36 courses. If any coefficient exceeds 3°, the table is compiled in 10° intervals, and for smaller coefficients - in 15° intervals. The input argument to the table is the compass heading.
The deviation table is signed by the person who determined it. The calculated values of deviation coefficients are also entered into the table.
Determination of deviation is carried out on the pole or at low speed of the vessel, and before proceeding to determine the deviation on a new course, it is necessary to wait 3 - 5 minutes necessary for the vessel to remagnetize. In each course, if possible, the deviation should be determined from 3 to 5 observations, and the result should be averaged. The accuracy of bearing or heading readings must be no less than 0.2°.
All main methods of determining deviation come down to comparing magnetic directions (bearings, headings) with directions measured by a compass. To calculate the deviation, the following formulas are used:
δ = MP - CP,
δ = WMD - OKP, (1)
δ = MK - KK
All methods for determining deviation differ only in the method of obtaining the magnitude of the magnetic bearing or heading. The main ways to determine deviation are:
- Determination of deviation along a target or along a fan of targets - is the most accurate way. The essence of the method is that at the moment of crossing the target, the compass bearing is noted.
The magnetic direction of the alignment is calculated based on the true direction and magnitude
The fan of alignments (Fig. 24) allows you to determine the deviation several times on the same course. The magnetic directions of the alignment fan are given in sailing directions or in descriptions of deviation polygons. If there are no alignments marked on the map in the area where the deviation is determined, then you can use the alignment of any objects (conspicuous towers, buildings, masts, capes, etc.). The magnetic direction of such a alignment is approximately calculated as the average of eight directions measured by compass on the main and quarter courses,
- Determining deviation from the bearing of a distant object carried out when there are no alignments in the work area. More often, this method is performed when the position of the vessel does not change or changes slightly, i.e. when the vessel is moored on a deviation pole, barrels, etc. The magnitude of the magnetic bearing can be obtained from a chart if the ship's position is known with high accuracy. If this is not possible, the magnetic bearing is again calculated as the average of eight measured compass points at the main and quarter directions according to formula (2). When a ship turns to a new course, its place on the ground does not remain constant, and at the same time the value of the MP changes. Obviously, the method can be used only when the change in bearing Δ from the average value does not exceed a certain permissible value. From Fig. 25 it can be seen that there is a relationship between the distance to the landmark D, the radius of the circle within which the position of the vessel (compass) changes, r and the angle Δ:
if you set Δ = 0.2°, then D = 300r. (3)
Thus, for example, with r = 100 m, the distance to the landmark must be at least 16.2 miles.
The method can also be used while the ship is moving, but in this case, a bearing on a distant object is taken at the moment when the ship passes in close proximity to a pre-installed buoy or pole. An approximate scheme of maneuvering when determining deviation using the indicated method is shown in Fig. 26.
Determination of deviation by comparison with the main magnetic compass usually carried out at a traveling compass, since there is no possibility of measuring bearing from it. The eight main and quarter courses are calculated using the heading compass, and the magnetic course is calculated using the CC of the main compass. The deviation of the traveling compass δп is obtained using the following formulas:
MK = KKgl + δgl. δp=MK - KKp (4)
or according to the working formula obtained after substituting the first equation into the second,
δp=KKgl - KKp+δgl. (5)
Comparison of compass readings, i.e. simultaneous fixation of heading, is carried out 3 - 5 times and the average value is displayed.
Determination of deviation from mutual bearings can be performed when there are no targets or distant objects in sight, but it is possible to take the compass ashore and install it on a tripod. The location where the compass is installed must ensure mutual visibility of the compass and the ship.
When determining deviation using any signal(lowering a conditioned signal flag, radio command, etc.) simultaneously measure the bearing from the shore and the ship. The bearing from the coast compass is MP + 180°, so it is easy to calculate the amount of deviation.
Determination of deviation by comparison with a gyrocompass- a common method on ships with a gyrocompass. The essence of the method is that the magnetic heading is obtained by determining the true one from the gyrocompass readings, and the declination is selected from the map. In the process of determining the deviation, the ship sequentially lies on eight main and quarter courses on the magnetic compass. On each course, the gyrocompass and magnetic compass courses are simultaneously noted (compared).
Deviation is calculated sequentially using the following formulas:
ik=gkk+Δgk,
MK = IR - d, δ = MK - KK
or according to the working formula obtained from them, (6)
δ = GKK-KK+(ΔGK - d),
where GKK n ΔGK is the gyrocompass heading and compass correction, respectively.
The comparison is performed 3–5 times, and the resulting deviations are averaged.
The method should be performed at the smallest speed, avoiding turns at a large angle, since this minimizes errors in the gyrocompass correction due to the influence of accelerations.
In addition to the methods discussed, a method for determining deviation is used according to the bearings of the heavenly bodies, if it is possible to measure the bearing of a star (Sun, Moon, star) and calculate its azimuth.
During sailing, it is necessary to use every opportunity to regularly determine the deviation on individual courses in order to monitor the reliability of the deviation table. To do this, they most often use definitions of compass corrections by alignments, by bearings of celestial bodies, and by comparison with a gyrocompass.
3.4. The principle of operation of the gyrocompass, taking into account errors in its readings. Methods for determining the gyrocompass correction.
The main heading guidance device is the gyrocompass. The basis of all gyroscopic direction indicators is a gyroscope (a rapidly rotating solid body), and the operation of these direction indicators is based on the property of the gyroscope to maintain the direction of the rotation axis in space unchanged without the action of moments of external forces.
The principle of operation of a gyrocompass can be described using a simplified diagram shown in Figure 27. The simplest gyrocompass consists of a gyroscope suspended inside a hollow ball that floats in a liquid; 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. Let's assume that the gyrocompass is located at the equator, and the axis of rotation of its gyroscope coincides with the west - east direction (position a); it maintains its orientation in space in the absence of external forces. But the Earth rotates, making one revolution per day. Since a nearby observer rotates with the planet, he sees the eastern end (E) of the gyroscope axis rising and the western end (W) descending; in this case, the center of gravity of the ball shifts to the east and upward (position b). However, the force of gravity prevents such a shift in the center of gravity, and as a result of its influence, the gyroscope axis rotates so as to coincide with the axis of the Earth’s daily rotation, i.e., with the north-south direction (this rotational movement of the gyroscope axis under the influence of an external force is called precession) . When the axis of the gyroscope coincides with the north-south direction (N-S, position c), the center of gravity will be in a lower position on the vertical and the cause of precession will disappear. By placing the “North” (N) mark on the place of the ball where the corresponding end of the gyroscope axis rests, and correlating the scale with the required divisions, you get a reliable compass. In a real gyrocompass, compensation for compass deviation and correction for latitude are provided. The action of the gyrocompass depends on the rotation of the Earth and the characteristics of the interaction of the gyroscope rotor with its suspension.
a B C)
Fig.27 Operating principle of the gyrocompass
To reduce the time of arrival at the meridian, gyrocompasses have a device for accelerated alignment to the meridian. If, using such a device, the SE of the main body is installed and held in the meridian with an accuracy of 2÷3°, then the time to reach the equilibrium position is reduced to 1÷1.5 hours (min 45 min.) The main axis of the SE of the working main body on a moving ship due to the presence dynamic and static errors are located in the direction of the gyroscopic meridian, which does not coincide with the true meridian.
Dynamic errors:
speed error, which arises due to the angular velocity of rotation of the true horizon plane due to the movement of the vessel along the surface of the Earth. This error is eliminated in the GC using a special counting and solving mechanism-corrector of the GC (by introducing IR, V, φ into it); inertial errors of type I and II, which arise when the course and speed of the vessel changes. At the end of the maneuver, the main body reaches a new equilibrium position in 25-30 minutes. These errors are eliminated in the HA by adjusting the period of undamped oscillations of the HA SE (84.3 min.) and the use of an oil damper in the CE;
the error due to pitching, which is caused by the swinging of the main body element relative to its main axis. Eliminated by stabilization of the SE in the horizontal plane.
Static errors: presence of friction in gyromotor suspensions; inconsistency of rotation speed of gyromotor rotors; inaccurate installation of the main device in the vessel's DP; action of magnetic fields. These errors, which characterize the stability of the operation of the hydraulic system on a fixed base, are determined experimentally. If it is possible to eliminate all the indicated errors, then the main axis of the GC SE is set in the direction of the true meridian (NI), and the tracking system allows this direction to be directly recorded and transmitted to the GC repeaters. The guiding moment of the GC is many times greater than that of the MC and does not depend on the Earth's magnetic field. However, with increasing latitude (φ), it decreases in proportion to cos φ, and at high
at latitudes (> 75°) the HA works less reliably.
Laboratory work No. 1
Magnetic compasses UKP-M and KMO-T
Goal of the work:
1. Study the principle of operation and structure of the UKP-M magnetic compass.
2. Study the principle of operation and structure of the KMO-T magnetic compass.
Lesson plan
1. Familiarization with the principle of operation and structure of the UKP-M magnetic compass.
2. Familiarization with the principle of operation and structure of the KMO-T magnetic compass.
Theoretical provisions
Design of the UKP-M magnetic compass
Magnetic compasses are used on ships as a course indicator, as well as to determine the ship’s position at sea using the bearings of coastal landmarks and celestial bodies. A compass used for direction finding and course control is called main. It is installed on the upper bridge in the center plane of the vessel or, as an exception, close to it. The compass located in the wheelhouse, according to the readings of which the helmsman keeps the ship on a given course, is called travel.
The sensitive element of the UKP-M magnetic compass is a six-pointer magnetic system (Fig. 1.1), placed in a pot with a supporting liquid. The sensitive element has a circular scale for reading the ship's heading. A magnetic system with a scale is called magnetic compass card, centered using a pin.
Since the ends of the arrows 1 are on the same circle and at given angles with respect to the diameter of their magnetic system, then this automatically eliminates the deviation coefficients of higher orders with sufficient accuracy for practice. This circumstance allows in all cases of shipboard practice to limit ourselves to determining the residual deviation of the compass only on eight equally spaced compass or magnetic courses.
In addition, this arrangement of the arrows also ensures equality of the moments of inertia of the card relative to any equatorial axis of its disk with divisions, which eliminates random vibrations of the card itself during the rocking of the ship.
| Fig.1.1 Magnetic compass card |
The frame of the card (Fig. 1.1) consists of a float 2 , made of thin sheet brass with a rim, cone 7 equipped with an agate firebox 3 and fastening screw 4 to her, a paper disk 5 and support disk 6 . Cone 7 serves so that the pot can acquire an inclination angle of ≤ 12° on a pin screwed into the pot column completely, without touching this column.
Paper disk 5 divided into 360° every 1°, with numbers indicating tens of degrees, starting from 0°. Latin letters indicate the main and quarter directions.
The compass pot with the liquid in which the card is located is installed in a gimbal suspension in the upper part of the binnacle, intended for suspending the magnetic compass and placing the deviation device. The binnacle is attached to the upper deck and, as a rule, is located in the centerline of the ship. This arrangement provides the most favorable magnetic conditions for the operation of a magnetic compass.
There is a hole on the side wall of the pot that is closed with a screw cap. Through the indicated hole, the kettle is filled with a supporting liquid (an aqueous solution of ethyl alcohol with a strength of 43º), which does not freeze down to -26º. If there are air bubbles in the main chamber of the pot, they must be removed. To do this, the compass bowl is carefully turned over with the glass lid down and rocked around the horizontal axis, or, after removing the light bulb socket from the cup with the weight, lightly press the diaphragm plug several times. If these measures do not give the desired result, then you should add a certain amount of compass liquid to the kettle.
The compass kit includes a direction finder - a device for finding direction of objects and celestial bodies, as well as for determining heading angles.
A magnetic compass mounted on a non-magnetic ship shows the magnetic heading ( MK ), different from the true course ( IR ) by the magnitude of magnetic declination d :
IR = MK + d(1.1)
Ship's iron affects magnetic compass readings. In its reference - compass course ( QC ) – an error appears, called deviation δ . The general correction of the magnetic compass will be
∆ = d + δ.(1.2)
The true course of the vessel is determined from the expression
IR = CC + ∆, (1.3)
IR = CC + δ + d(1.4)
Compass course ( QC ), corrected by deviation δ , determines the magnitude of the magnetic course ( MK ),
MK = KK + δ(1.5)
In Fig. 1.2 presents relations (1.1)-(1.5). Magnetic compass deviation δ - This is an error that includes four components:
- constant deviation, arising from soft iron;
- semicircular deviation, caused mainly by the influence of solid ship iron;
- quarter deviation, caused by soft ship's iron;
-roll deviation, which occurs during the roll and pitching of the ship, and is mainly caused by the action of the vertical ferromagnetic elements of the ship's hull.
To eliminate these three deviations, the design of the magnetic compass has three independent devices.
Semicircular deviation compensators - two pairs of permanent destroyer magnets installed inside the compass. One pair is longitudinal magnets, the other is transverse. Eliminating semicircular deviation involves finding the proper position of the magnets using carriages or flywheels IN And WITH .
The fourth deviation compensators are made in the form of horizontal plates made of soft ferromagnetic material, which are installed outside the binnacle, in its upper part.
A vertical permanent magnet for eliminating heel deviation is placed inside the binnacle in the deviation pipe. Flywheel Z set its appropriate position.
A magnetic compass makes it possible to determine not only the course of a ship, but also the heading angle and bearing of any object.
Magnetic compass checks
Checking the card for stagnation
Stagnation of the card is caused by dry friction in the suspension of the sensitive element. To determine the amount of stagnation, the card is deflected at a small angle, influencing it with some kind of magnet. After the magnet is removed, it should return to the original reading. If there is stagnation, the card will be installed in a different position. The difference in readings characterizes the amount of stagnation.
To increase the accuracy of determining the stagnation angle, readings from the card are measured through the prism of the direction finder. The work is carried out on shore in the following sequence:
– set the direction finder to a reading of 0° in the azimuthal circle and turn the compass binnacle so that the reading of 180° appears under the direction finder prism ( S) cards.
– using a small magnet, they deflect the card by 2 - 3 degrees, remove the magnet and, after the card has calmed down, take a reading under the direction finder prism (with an accuracy of 0.2°); the procedure is repeated several times;
– find the stagnation angle as the average difference in readings compared to the initial value of 180°.
The stagnation of the card is considered normal if the stagnation angle does not exceed 0.2°. If there is a lot of stagnation, it is necessary to sharpen or replace the compass pin.
