A properly adjusted compass shall have a residual deviation within 3° in vessels 500 or more gross tonnage and, +/- 4° in vessels below 500 gross tonnage. Accuracies shall be within +/- 2° for safe navigation. A special regulation applies to inland vessels, where the maximum residual deviation may be +/- 6°.
The location of the compass on board the vessel is not insignificant for ensuring reliable operation of the magnetic compass. It is particularly important to ensure that the magnetic free zone around the compass is complied during building and esured during operation.
This is a distance of the magnetic compass to any magnetic materials. This distance should be assumed to be spherical around the compass. Accordingly, A-magnetic steel or other non-magnetic materials should be used within this area.
Furthermore, the distance to electronic devices, also called “magnetic safe distance”, must be taken into account. This distance is indicated on the back of every electronic device used in merchant shipping.
G2. Magnetic compasses should be adjusted when:
- every two years, under German flag (or depending on the interval of the responsible flag state).
- after a dry-docking phase.
- after significant construction measures.
- Magnetic compasses should be adjusted when:
- they are first installed;
- they become unreliable (e.g. after an accident);
- repairs or structural alterations have been made to the ship that could affect its permanent and/or induced magnetism;
- electrical or magnetic equipment close to the compass is added, removed or altered;
- the recorded deviations are excessive, as per the limits defined in G.1, or when the compass shows physical defects; or
- at any other time deemed necessary by the master for the safety of navigation.