Deflection of the magnetic compass and its destruction

The steel set of the ship’s hull and its skin acquire magnetic properties from the moment of construction. In the Earth’s magnetic field, all longitudinal, transverse and vertical connections of the vessel are magnetized differently. Ship’s iron is magnetically divided into hard and soft.

The magnetic needle of a compass mounted on a ship is influenced by the magnetic forces of hard and magnetically soft iron, and their effect is different. In addition, as a result of the action of magnetic forces arising from the magnetic field created by various working ship units, circuits with current, the compass needle deviates from the magnetic meridian. A vertical plane passing through the poles of a magnetic needle suspended by the center of gravity on a ship having free rotation around a vertical axis is called the plane of the compass meridian at a given point of the ship.
Significant deviation creates great inconvenience when using a magnetic compass. Therefore, deviation is eliminated on ships by artificially creating forces in the center of the compass that are identical in nature, equal in magnitude and opposite in direction to the forces causing deviation. To do this, bars of hard and soft iron are placed near the compass in special devices. The compass will be an autonomous and reliable cursor pointer in the event that the forces causing the deviation are compensated.
Destroying compass deviation on a ship is a laborious job, usually performed by specialist deviators, and sometimes by boatmasters.

After the destruction of the deviation, the ship’s magnetic compasses determine the residual deviation, which usually does not exceed 2-3 °. It is found from observations on eight equally spaced main and quarter courses.

To determine the residual deviation of the compasses, there is

there are several ways. It is most often defined by:

the gates;
bearing of a distant object;
mutual direction finding;
the direction of the heavenly bodies.

The simplest and most accurate way is to determine the deviation along the targets. To do this, following one of the courses, cross the line of leaf signs, the magnetic direction of which is known. At the moment of crossing the shutters, the compass bearing of the shutters is noticed by the magnetic compass.

Our company has specialists who have the right to carry out repair, adjustment, delivery, deviation work on magnetic compasses and lags produced by JSC KIPZ and not only.

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Original:

§ 16. Девиация магнитного компаса и ее уничтожение (flot.com)