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Compass regulation is the method of analyzing and compensating for deflecting magnetic forces on a ship's magnetic compass.
How often a compass has to be adjusted?
The magnetic compass shall be adjusted:
How magnetism is created in the earth and what exactly it is made of is a complex topic that has not yet been fully clarified. From a navigator's point of view, it is reasonable to assume that there is a huge bar magnet in the earth's interior, the position of which corresponds approximately to the earth's axis. The magnetic south pole of this bar magnet is close to the geographic north pole and the magnetic north pole is close to the geographic south pole. The magnetic field lines run between the magnetic poles.
The angle between magnetic north (south pole of the Earth's bar magnet) and geographic north is called variation.
A magnetic compass aligns itself with the Earth's magnetic field lines if it does not experience any further magnetic deflection.
The variation can be found on the nautical chart, where it is indicated for a specific year. Since the Earth's magnetic field is not constant but is always moving, an annual change in the field and thus a change in variation must be taken into account.
In the middle of the century before last, ships began to be built from steel, and only then did effects occur that deflected the magnetic compass further than normal or in a different way than expected. It took a while to understand what exactly caused this deflection. Today we know that a ship develops permanent magnetism during its construction phase due to the permanent induction of the earth's magnetic field. This is also referred to as fixed magnetism in iron. After a ship is launched, the ship itself is a magnet that influences the magnetic compass. The earth's magnetic field and the ship's magnetic field compete with each other.
Since different types of iron are used in a ship and one can roughly say that the harder the steel, the stronger the magnetism that forms in it, a ship has zones with permanent, semi-permanent and inducted magnetism.
The sum of these, which can be briefly summarized under the ship's magnetism, leads to the aforementioned deviation.
The magnetic compass is therefore subject to variation and deviation. Both errors together describe the magnetic compass variation and thus the angle between magnetic compass north and true north.
When adjusting a compass, a specially trained and certified adjuster uses analytical methods to estimate the ship's solid, semi-solid and volatile magnetism and then compensates for it. The trick is how well a adjuster can estimate the values and then compensate for them by setting permanent magnets and soft iron correctors. In other words, reducing the error to a minimum. Ideally, the deviation can be compensated for entirely.
Do I need to compensate my compass? Isn't it enough if I know the deflection?
SOLAS Chapter V, Regulation 19, Paragraphs 2.1.1, 2.1.2, 2.1.3 and 2.2.1
Apart from the legal requirements for compensation, it would also not be advisable to sail with an uncompensated compass.