This magnetic compass is constituted by a compass rose, with a graduation from 000º to 360º, with a pointer that spins inside an antifreeze liquid.
Nowadays this compass isn’t used that much on board. However, this device is kept on board in case of emergency, like a malfunction on the gyroscopic compass.
The magnetic compass has the following parts:
The magnetic compass has the obligation of being steady, which means, indicating with precision the bow of the ship, without value oscillations.
It also must be sensitive, so the alternations of the bow are shown on the compass.
On board there are two magnetic compasses:
There is one that is used to see the ship’s bow to orientate the vessel and It is usually located on the bridge.
The other one is located on top of the bridge, in a way that is free from any ship’s magnetic influences. It serves to take bearings and the course.
Magnetic compass deviation:
It’s the angle between the magnetic north and the compass north, being the compass north defined by the line which the vessel is orientated when it can’t eliminate the magnetic field of the vessel.
The compass deviation varies having in consideration the metals of the ship and its bow.
The calculation of the compass deviation (δ ) is determined through the Variation (V) e Declination (D) using the following formula:
V = D + δ