Even in times of satellite navigation via GPS, radar and the automatic identification system A.I.S., the magnetic compass is still the most important navigation instrument on board. This applies equally to commercial vessels and pleasure craft. The biggest advantage of the north pointers is that they function independently of any power supply. A power source is only required to illuminate the compass rose. The fact that the compass rose always points exactly north is due to the earth's magnetic field. The magnetic field lines, according to which the compass is orientated, run (approximately) from pole to pole.
The property that magnetic iron stones (also known as magnetite) orientate themselves in a north-south direction was already being used by Chinese sailors in the 11th century. They navigated with a so-called wet compass, whose magnetic needle floated on a liquid surface.
Modern compasses also work with liquids, but the fluid no longer serves as a frictionless bearing for the needle, but is used to dampen the compass card. Magnetic compasses for boats and yachts are predominantly designed as so-called spherical models.
In this design, a disc fitted with magnets, the compass card, is rotatably mounted on a tiny gemstone tip. This means that the rose, which is labelled with the cardinal points and degrees, is suspended extremely friction-free and can be turned very easily. To dampen the movements of the boat transmitted to the compass and to protect the rose, a ball made of plastic or, in the case of expensive devices, glass is built around it and filled with oil. As this process is easier to describe than to carry out, the design and production of compasses is a matter for specialists.
Downloads:
download
