Why Does A Magnetic Compass Installed On A Ship Need To Be Calibrated?

Abstract:  This article mainly focuses on the principle of magnetic compass, the  change of ship magnetism and its influence on the magnetic compass, the  relationship between ship navigation and magnetic compass. The basic  principle of magnetic compass is introduced on the one hand, and the  other is explained on the other hand. Magnetic compass plays an important role in ensuring the safe navigation of ships.

1. The principle of magnetic compass

Our ancestors discovered as early as 2,600 years ago that "magnets call for iron, or quote it." "Ci" is now "magnetic." Later, he invented the "Dinan" and "Dinan" to guide the North and create a compass. This is a great contribution of the Chinese nation to world civilization.

The  earth is a large magnet. It has a magnetic field on its surface. Its  two poles are close to the earth's two poles, but they do not coincide  and it moves very slowly. We  call the pole near the north pole of the earth the magnetic north pole,  and the pole near the south pole of the earth is called the magnetic  south pole.

A  magnetic needle with a fulcrum in the middle, when no ferromagnetic  matter is around it, one end of the magnetic needle points to the  magnetic north pole, and the other end points to the magnetic south  pole.

Everyday we use the magnetic compass, its core part is the floating chamber. In order to obtain sufficient north force. Usually two or four magnetic bars are installed in the floating room. The  magnetic bar is under the action of the earth's magnetic field, with  one end pointing to "north" (ie magnetic north) and the other end being  "south" (ie magnetic south). Then fix a dial around the float chamber and make a baseline on the compass bowl. So we can see the direction. However, the “North” referred to by the compass refers to magnetic North is not true north of the Earth's true meridian. The error between magnetic north and true north is called magnetic difference.

2. Changes in the magnetic properties of ships and their effects on magnetic compasses

General ships are made of steel. In the earth's magnetic field, steel is magnetized and magnetic.

Ships are usually equipped with generators, wires and a large number of electrical equipment. These electrical devices also generate magnetic fields during use. This magnetic field also has an effect on the ship itself - the hull is magnetized.

When  a ship is docked at the same pier for more than one month, due to the  magnetization of the Earth’s magnetic field, the original magnetic  properties of the ship will also change.

When the ship is subjected to severe shocks, the magnetic field of the ship itself will also change.

The ship was beaten by the big waves at sea and the ship was subjected to other ship collisions. Or he himself accidentally collided with the dock when he was on the dock. Both can make the ship's own magnetic change.

When  the ship is repaired, such as changing the steel on the ship or adding  equipment, especially near the magnetic compass, even smaller steel  parts will have an effect on the magnetic properties of the ship.

When  a ship accidentally catches a fire shed, even if it is a partial fire,  it will have a greater impact on the magnetic properties of the ship. At the same time will also affect the magnetic compass.

When ships are loaded with steel (including magnetite). Because these steels are magnetic. Therefore, the magnetics of the hull have changed.

It  is particularly worth noting that when the ship is loaded and unloaded  with loose steel blocks by a magnetic crane, the hull will be heavily  magnetized and serious deviations will occur in the magnetic compass on  the ship. And after a long time the magnetic compass on the ship is unstable! Big changes!

The magnetic compass is mounted on the boat. In addition to the effect of the Earth's magnetic field, it is also affected by the magnetic field of the hull. Various ships have different magnetic sizes. The effects of the magnetic compass installed on this boat are also different. As many as 170 degrees to 180 degrees, ranging from 10 degrees to 20 degrees. Only after measuring can I know.

3, ship navigation requires magnetic compass

Although modern technology gave the ship a precise positioning satellite locator. However, every ship must install "ancient" magnetic compass. It is an essential pointing device for the navigation of ships. It is also a reliable guarantee for safe navigation of ships.

The  magnetic compass installed on the ship is not accurate due to the  magnetic influence of the hull. Inaccurate pointing is impossible to use  to navigate. Therefore, the magnetic compass must be corrected. Finally, it measures its error in each major heading and creates a self-deferred table. This magnetic compass can be used navigation to ensure the safety of the ship.