When does the magnetic compass need to be corrected for deviation

When purchasing a marine magnetic compass, you may find it often comes with a set of calibration equipment. Whether these devices are necessary, why they're used, and when to use them, many users are unclear after purchasing. This article will answer your questions.

Overview

What is magnetic compass deviation?

The error of a magnetic compass includes magnetic deviation and self deviation. Magnetic deviation is the angle between magnetic north and true north due to inconsistency between the magnetic pole and the geographic pole, also known as magnetic declination. Self deviation is the effect of the ship's steel being magnetized by the Earth's magnetic field on the magnetic compass, causing the magnetic needle to deviate from magnetic north, forming a difference angle of up to several tens of degrees. Correcting deviation involves placing correctors around the compass that can produce forces opposite to the ship's magnetic field, using magnetic rods and soft iron to offset the effects of permanent and induced ship magnets on the magnetic needle. The residual deviation after correction should be determined and made into a deviation table or curve graph, and its absolute value should not exceed 3°. The main characteristic of deviation is that it changes with the heading, and corresponding deviation correction equipment should be used for different headings.

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When is it necessary to correct the deviation?

1. A newly built ship's magnetic compass.

2. A ship's magnetic compass after repair (including major repairs, intermediate repairs, and annual repairs).

3. A ship's magnetic compass subjected to severe vibrations (such as collisions, groundings, reef strikes, lightning strikes, etc.).

4. After the installation position of the compass on the ship changes.

5. When the standard magnetic compass deviation exceeds ±3° (the steering compass deviation exceeds +5°) without considering constant deviation.

6. The ship's magnetic compass when it docks in a fixed heading for more than one month.

7. A ship's magnetic compass after unloading a large quantity of ferromagnetic cargo.

In summary, the deviation correction equipment provided with the magnetic compass is crucial for its normal use and maintenance. After purchase, be sure to keep these accessories well. If you did not choose the matching equipment at the time of purchase or if accessories are lost, you can also contact us for a repurchase.