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Compass - Compass correction

Compass - Compass correction: Encyclopedia II - Compass - Compass correction

A ship's compass must be corrected for errors, called compass deviation, caused by iron and steel in its structure and equipment. The ship is swung, that is rotated about a fixed point while its heading is noted by alignment with fixed points on the shore. A compass deviation card is prepared so that the navigator can convert between compass and magnetic headings. The compass can be corrected in three ways. First the lubber line can be adjusted so that it is aligned with the direction in which the ship travels, then the effects of per ...

Compass: Encyclopedia II - Compass - Compass correction

Compass - Compass correction

Main articles: Magnetic deviation, and [[{{{2}}}]], and [[{{{3}}}]], and [[{{{4}}}]], and [[{{{5}}}]]

A ship's compass must be corrected for errors, called compass deviation, caused by iron and steel in its structure and equipment. The ship is swung, that is rotated about a fixed point while its heading is noted by alignment with fixed points on the shore. A compass deviation card is prepared so that the navigator can convert between compass and magnetic headings. The compass can be corrected in three ways. First the lubber line can be adjusted so that it is aligned with the direction in which the ship travels, then the effects of permanent magnets can be corrected for by small magnets fitted within the case of the compass. The effect of non-ferromagnetic materials can be corrected by two iron balls mounted on either side of the compass binacle. The graph of the compass deviation can be understood using Fourier series. The coefficient a₀ representing the error in the lubber line, while a₁,b₁ the ferromagnetic effects and a₂,b₂ the non-ferromagnetic component.

Fluxgate compasses can be calibrated automatically, and can also be programmed with the correct local compass variation so as to indicate the true heading.