The compass is a device for geographical orientation, based on a magnetized needle that tends to align with the magnetic north/south.

How a compass works

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The compass is an ancient instrument used for the detection of cardinal points. Inside, it is equipped with a magnetized needle that exploits the properties of the earth's magnetic field to align itself in its direction.

In fact, the terrestrial globe can be compared to a large magnet with its two poles positioned near the two geographical poles.
So the needle is oriented towards magnetic north/south, which is different from the geographical one also called true North/south or terrestrial, and the difference between the two surveys is identified as magnetic declination that varies from one geographical location to another.
Therefore, through the compass, knowing the magnetic declination at that point, we will have the possibility to determine also the geographic North/South.

Components and types of Nautical Compass

The components of a compass are:

  • The mortar or case, is the outer antimagnetic casing
  • Suspension pin or point, fixed to the bottom of the mortar
  • Sensitive element or crew, is formed by parallel magnetic needles resting on the upper extremity of the pin on which they are free to turn
  • The (wind) rose is a graduated disc from 0 to 360 degrees, fixed on the magnetic needles
  • Liquid, it is used to support the rose and to make its rotation more stable, soft, progressive and harmonious.
  • Dome or dome, is the transparent top that allows you to read
  • The line of faith represents the direction of the bow and indicates on a boat the degrees of the course with respect to the magnetic north
  • Compensating magnets, used to compensate for the difference between magnetic and true (geographical) north
  • Membranes, serve to seal the connection between mortar and shell, thus preventing the leakage of the liquid

Two types of compasses can be used in the nautical sector:

  • As a bearing, it is used to identify the direction in degrees with respect to a target
  • For navigation, are those normally installed in a fixed way on the boat in the dashboard

The types of navigation compasses, are distinguished by the rose:

  • Flat, also called reverse reading, in fact the reading takes place beyond the pivot towards the bow
  • Concave or direct reading, the reading takes place in front of the observer

The compasses are also switched off by the type of installation:

  • Binnacle or base mounted, installs directly on a shelf
  • Flush-mounted, it can be installed by flush-mounting the mortar and projecting the shell.
  • On bracket, comes complete with its bracket that makes the compass easily removable

There are also different models depending on the type of boat:

  • For powerboats, binnacle, recessed or bracket-mounted boats are well suited
  • For sailboats, they are normally installed recessed on a vertical surface and are equipped with an inclinometer to measure even the heeling
  • For rescue boats, normally supplied with a wooden container and serves as a compass of respect

Compass issues and maintenance

As long as the liquid inside maintains its original viscosity and this does not escape creating a bubble in the upper part, the compass is able to operate optimally and there should be no problems related to its operation (except those related to its compensation).

So it's important to check on the compass:

  • The presence of any bubbles
  • That the liquid retains its original transparency

If there is a bubble or the liquid loses its original transparency, the compass must be replaced or sent for service to a specialized center, to fill or replace the liquid.