Maintenance And Maintenance Of Ship's Magnetic Compass

1 Introduction

Magnetic compass, also known as "magnetic compass", is a navigational instrument that provides directional reference or horizontal reference on ships, used to mark the heading, observing object's azimuth, and indicate the longitudinal and heel angle of the ship. It is gradually developed on the basis of ancient China's Sinan and compass. It is a compass made by using freely supported magnetic needles to stably point to the magnetic north under the action of the geomagnetic field.

Nowadays, although the role of navigational instruments is becoming less and less obvious with the development of digitalization, when many critical situations occur, modern navigational instruments fail, and magnetic compasses that do not require any external conditions can often play a huge role. Some small and medium-sized ships, especially port-based ships (tugboats, construction ships, transportation boats), fail to meet the relevant requirements for the equipment, use, and management of magnetic compasses. Therefore, understand the current status of the use of magnetic compasses in port-based ships and find out what is incorrect The reasons for using magnetic compasses and improvement methods are of great significance to the safety of maritime navigation and the development of navigation. Therefore, we must correct our thinking, re-examine the status of magnetic compasses in the navigation industry, and increase the importance of maintaining and maintaining magnetic compasses. Awareness.　　

2. The significance of maintenance and maintenance of the magnetic compass

Since the 21st century, despite the rapid development of high-tech instruments, magnetic compasses are still widely used due to their reliability and ease of use. They are essential navigation aids for ships. At the same time, ship drivers must understand magnetic Compass maintenance and maintenance to ensure the safety of navigation.

For example, at 21:30 on March 20, 2006, the "Chang'an 119" ship, which belongs to Chang'an Shipping Co., Ltd. of Wenling City, Zhejiang Province, used the compass to observe the light beacon when it sailed to the 12# light float at the entrance of Yingkou. The compass did not correct the deviation according to the regulations. The compass pointing error reached 15 degrees. The pilot underestimated the situation, resulting in wrong navigation. The ship ran aground on the shallows of the Yingkou port area. The responsibility was entirely that the ship’s magnetic compass did not "play" it well. So that the accident happened. In addition to the problems in use, navigators should also have sufficient understanding of the pointing principle and maintenance of magnetic compasses.

First of all, in modern times, ships in the world have gradually evolved from wooden hulls in ancient times to steel hulls today. The magnetization of the steel components of the ships will act on the magnetic compass, causing the magnetic needle to deviate from the magnetic north. The difference angle is called the compass deviation. Compass deviations are as high as tens of degrees and must be corrected. The main feature of the deviations is that they change with the heading, and different headings should be corrected with corresponding deviations. For example, when a ship is navigating in strong winds and waves, the zigzag navigation method is generally used to keep the ship sailing along the 2-3 compass points on the left or right. Danger to the ship.

Secondly, the absence of a standardized marine magnetic compass correction field will cause many ships’ magnetic compass deviations to be uncorrected for a long time. The deviations of many ships are much higher than the residual deviation standards stipulated by the national maritime department. Ship navigation safety and one of the important hidden dangers. Some ships are equipped with an AIS system, and the heading signal of the system is provided by a magnetic compass. Because the magnetic compass cannot point accurately and cannot provide reliable heading data, the information of the AIS system ship is disturbed, causing other ships to misunderstand and cause maritime accidents. accident.

3. Current status of maintenance and maintenance of marine magnetic compass

Due to the increasingly perfect ship navigation and positioning system, especially the rapid popularization of GPS, ASI, electronic chart, multi-function radar and other instruments on ships in the port, some navigators pay less attention to the scientific use and management of magnetic compasses. At present, Many ships, especially civil ships, only rely on GPS when navigating. The magnetic compass installed on the ship is often in a standby state. The direction of the ship is dangerous to the ship’s navigation.

From March to June 2007, Yingkou Maritime Safety Administration conducted an investigation on 50 port-operating ships (tugboats, construction ships, and transportation boats) in Yingkou Port, and found that 41 ships’ magnetic compasses were assembled, used, managed, and corrected. None of them met the relevant requirements, accounting for 82% of the ships under investigation, which brought great hidden dangers to the safety of maritime navigation. Many ship’s magnetic compasses are installed incorrectly, not maintained in time, and the maintenance method is not appropriate, causing the compass to not point normally. Research and analysis have found that the following problems mainly exist:

(1) Among the port-operated ships under investigation, 15 ships were equipped with steering compasses, and there were neither standard compasses nor backup compasses. Although 20 ships were equipped with standard compasses and steering compasses, there was no difference between the two. With any reliable contact, most ships cannot take the initiative to correct the magnetic compass as required, and only 15 ships can meet the requirements of the International Maritime Organization (MIO) "Recommendations on the Installation of Magnetic Compass".

(2) Due to the small tonnage of ships in the port, the structural layout of ships is subject to certain restrictions. For example, the searchlights installed next to the standard compass are often spaced much closer than the "minimum allowable distance of 5 meters." Many port ships are equipped with civil air-conditioning, and the external hanger is installed on the compass deck, which has a great impact on the standard compass. Due to the small pilot room of the port, the layout of ferromagnetic components around the steering compass is asymmetrical, and the amplifier, depth sounder display, radar, microphone, and iron console are too close to the compass, making the steering compass unable to indicate the course normally.

(3) Some ships do not install the magnetic compass on the center line of the ship, and the baseline does not overlap with the bow and stern lines (just parallel). For some special reasons, the compass was installed on the side of the bridge on the side of the bridge due to special reasons, so that the baseline was very different from the bow and stern lines, and the direction indicated by the compass was not the heading of the ship.

(4) Some construction ships have asymmetrical distribution of steel components, and ferromagnetic objects are too close to the compass, etc., which cause the compass to have a large uncorrectable deviation, which makes it difficult for the magnetic compass to play its due role.

(5). Electrical equipment and cables and wires are randomly installed near the compass of some ships. These factors will have a great impact on the magnetic compass, and there will be a large deviation, which makes the magnetic compass unable to point accurately.

(6) Most of the surveyed construction ships’ magnetic compasses were not maintained in time or the maintenance methods were improper, resulting in the compass not pointing normally. During the investigation, it was found that some ship standard compasses had no compass cover, and the surface of the card was discolored and deformed due to long-term sun exposure, and even water entered the compass cabinet, causing damage to the compass; some ship compass bubbles were not eliminated in time, and the Changping ring was not lubricated. The ship’s skid wood is severely corroded, and the compass is not level if it is not replaced in time; some ships do not have a self-difference corrector, and some ship correctors are improperly stored, which causes the correction to be lost; some ship's azimuth instruments are not stored properly and deformed and cannot be used.

4. Maintenance and maintenance of magnetic compass

4.1 Daily inspection and maintenance of magnetic compass

4.1.1 Checking the baseline of the magnetic compass

When installing a magnetic compass, the standard compass should be installed in the fore and aft surfaces of the ship, and the compass baseline should coincide with the fore and aft surfaces. If the baseline of the magnetic compass is installed incorrectly, compass errors will occur. Check the baseline of the standard compass, usually by using the centerline of the foremast and the centerline of the chimney.

4.1.2 Elimination of bubbles

If there are bubbles in the compass basin, it will hinder the reading of the compass. When the bubbles are serious, it will affect the stable support of the compass by the liquid, which will cause errors in the observation course and the orientation of the object, which must be eliminated.

Causes of bubbles:

1) The water tightness of the Luopen is not good, the liquid seeps out, and the air enters the Luopen;

2) Caused by air escaping from the floating chamber.

Notice:

① If the glass gasket on the upper cover of the bowl is aging and the screw on the cover or the bottom of the bowl is loose, measures should be taken in time;

② If the basin body is not tightly watertight or damaged, send it to the factory for repair or replacement.

Elimination method:

When removing bubbles, put the basin on its side and place the bubbles in the basin under the liquid injection hole. Unscrew the liquid injection hole screw and inject the compass liquid until the liquid comes out, and then tighten the liquid injection hole screw. For a compass basin with a basin divided into upper and lower chambers, after the upper chamber is filled with liquid, the compass basin should be placed upright to measure the liquid level in the lower chamber. If it exceeds the specified height, the excess liquid should be discharged from the liquid injection hole in the lower chamber, and if it is not enough, liquid should be added.

4.1.3 Check the sensitivity of the compass dial

The friction between the shaft cap of the compass dial and the shaft needle must be very small. If the jewel in the shaft cap is damaged or the shaft needle is abraded, the dial will not rotate properly, and the directivity will be lost in severe cases.

Inspection Method:

1) Conditions: The ship is fixed at the wharf, the ship-shore machinery is not working and the deviation is not large;

2) Accurately record the scale of the compass on the bow baseline (ie Luo course);

3) Use a small magnet or iron to guide the compass to the left (right) by 2° ~ 3° and then quickly remove it;

4) After the compass balance is restored, the difference between the heading reading and the original heading value should be less than 0.2°;

5) Do the same check again in the right (left) direction.

4.1.4 Checking the magnetic force of the compass

After the magnetic compass is used for a long time, the magnetism of its compass will decline, which affects the stability of the compass pointing. The magnetic strength of the compass is directly related to the swing period of the compass. The half-period of the compass swing can be used to determine the magnetic strength of the compass.

Inspection Method:

1) Move Luopen to a place where there is no magnetic interference on the shore, 1 meter above the ground;

2) Rotate the compass to make the head baseline align with the compass at 0°;

3) Use a small magnet to guide the compass to the left (right) by 40° and then quickly remove it, and the compass starts to swing;

4) Use a stopwatch to measure the time it takes for the compass 0° to pass the first baseline twice in a row, that is, the half cycle of the compass swing;

5) Make the same measurement to the right (left) direction;

6) Compare the measured half-period value with the standard value in the factory manual. If it is larger, it means that the compass has a large decrease in magnetism and should be sent to the factory for magnetization.

4.1.5 Relevant regulations of magnetic compass deviation correction

The deviation of the standard compass must not be greater than 3 degrees, and the deviation of the steering compass must not be greater than 5 degrees, otherwise it should be eliminated. The magnetic compass should be calibrated once a year, and the deviation table should be re-drawn and the deviation curve should be drawn. If the ship stays on a certain course for more than one month, it should be recalibrated.

In addition, when a large amount of ferromagnetic material is installed on the ship, or the structure of the hull is changed, or after the ship is repaired, or the ship is struck by lightning, stranded, collision, etc., the original ship’s magnetism should be recalibrated.

4.1.6 Inspection of the soft iron magnetization of the magnetic compass and inspection of the magnetic force of the correction magnet

Inspection of the magnetization of the soft iron ball: Check whether the soft iron ball is magnetized. The bow of the ship should be fixed in a certain heading. First, loosen the screws under the soft iron ball and put the two soft iron balls close to the compass. Rotate the red ball/green ball slowly to see if the compass degree changes. If the degree of the compass changes when any ball rotates, it proves that the soft iron ball has been magnetized.

Inspection of Ferromagnetization: Ferro is a soft iron rod without remanence, used to correct the asymmetric vertical soft iron rod (such as a chimney) before and after the magnetic compass. During the inspection, the bow of the ship should preferably be fixed to the east or west heading, where the influence of the Ferromagnetization on the two headings is the greatest. During the inspection, write down the heading reading first, then turn the Fuchs soft iron upside down and observe whether the compass degree changes. If there is any change, it proves that the Fuchs iron has been magnetized. Method to eliminate magnetism: place it on the ground for knocking, rolling or quenching and demagnetization. Replace it when the demagnetization is invalid.

Permanent correction of the magnetic bar magnetic inspection: the ferromagnetic bar used to eliminate the difference should be rust-free, and rust will make the magnetism subside. Also check the newly purchased magnetic bar, whether the color painted on the bar matches the magnetic pole.

4.2 Use and maintenance of magnetic compass

4.2.1 The use of magnetic compass

①The magnetic compass must be correctly calibrated for its deviation, and an effective deviation table must be prepared;

②The self-difference should be measured frequently at ordinary times;

③When measuring the azimuth of the object, pay attention to the level on the azimuth circle to keep the compass bowl level;

④ Ferromagnetic objects shall not be placed near the compass, so as not to affect the normal operation of the compass;

⑤ Properly adjust the focal length of the optical lens device of the reflection or projection compass to make the heading scale clearer;

⑥Check the magnetic compass regularly or at any time;

⑦When an abnormal phenomenon is found in the compass, it should be recorded in the logbook and reported to the captain;

4.2.2 Maintenance of magnetic compass

①The compass cap should be covered and the compass shield should be put on at ordinary times to prevent the scale from being deformed by the sun and water entering the compass cabinet during wave time;

②When the ship is docked and the compass is not in use, the compass lighting should be turned off;

③The moving parts such as compass bearing and Changping ring should be lubricated regularly;

④Keep the Luopen liquid colorless and transparent, and remove the bubbles in the Luopen in time. ；

⑤The optical lens surface of the projection or reflective compass should be cleaned regularly to make the scale reflected by the compass clearly visible;

⑥ To prevent the soft and hard iron corrector from rusting, the spare soft iron corrector should not be close to the permanent magnet; the spare correcting magnet should be close to each other, and avoid the influence of high temperature, severe vibration and other magnetic fields;

⑦When the azimuth circle is not in use, it should be stored in the box to prevent the azimuth circle from deforming due to collisions and other reasons.

4.3 Precautions for using magnetic compass

In order to ensure the safety of ship navigation, to conveniently and correctly judge whether the working condition of the magnetic compass is normal, and to keep the magnetic compass intact and seaworthy, you must always pay attention to the precautions when using the magnetic compass, that is, you should pay attention to the following when using the magnetic compass aspect:

①When using a magnetic compass, you should not carry iron objects with you, and check whether there are any iron objects added or removed near the magnetic compass, so as not to affect the deviation of the compass;

②The reading heading should be directly behind the compass to improve the accuracy of the reading. Observe the heading in wind and waves, and read the average value when the compass swings left and right; if the swing is large, it means that the tilt deviation has not been eliminated correctly. Use compass to observe the position of the object and keep the compass basin level.

③If the ship sails for a long time in a certain heading, the ship’s magnetism has been induced by the geomagnetic field for a long time, and it should be used only after 5-10 minutes after the ship has turned.

④After the compass is stable, the course can be read and the target bearing can be measured. When reading the course, look at the reading of the dial on the base line of the bow from directly behind the compass.

⑤When measuring azimuth and ship angle, push the azimuth circle forward to avoid random errors.

⑥The large equipment on the boat should be placed in the normal position at ordinary times, and the equipment used to eliminate the difference should not be moved at will.

⑦The compass error should be measured frequently during sailing, and the driving compass should be compared with the main magnetic compass.

5. Concluding remarks

This article mainly discusses the importance of the maintenance and maintenance of marine magnetic compasses and the precautions for their maintenance and maintenance. Although with the digitalization of navigational instruments, its role becomes less and less obvious. However, when many critical situations occur, modern navigation If the instrument fails, the magnetic compass, which does not require any external conditions, can often play a huge role.

In daily inspections of ship’s safety equipment, you should check the technical status of the magnetic compass on board and the date when the deviation table was set, so as to urge the use and management of the magnetic compass on board to keep the magnetic compass in good condition. Therefore, in daily work You should do a good job in the technical work on the magnetic compass discussed in this article.