Failure to maintain a magnetic compass in good condition or to monitor deviations may result in a vessel being delayed and potentially the vessel owner and master being prosecuted.

The Australian Maritime Safety Authority (AMSA) has issued Marine Notice to remind the importance of magnetic compasses for the safety of navigation, applying to “regulated Australian vessels” and certain foreign vessels. 
Vessel owners have responsibilities for ensuring that magnetic compasses are maintained in good order, adjusted and a table or curve of residual deviations is available. 
The performance of the compass should be monitored and, for a vessel more than 100GT, deviations recorded in a compass deviation book at regular intervals, ideally at least once every watch and also shortly after a large alteration of course.

If the observations for a magnetic compass show a deviation of the compass on any heading of more than 5 degrees, the compass must be adjusted by a qualified compass adjuster  to correct the deviation.

Annex G of ISO 25862:2009 also recommends that a compass should be adjusted when:
  • they are first installed;
  • they become unreliable;
  • repairs or structural alterations have been made to the vessel that could affect its permanent or induced magnetism;
  • electrical or magnetic equipment close to the compass is added, removed or altered;
  • they show any physical defects;
  • if a record of compass deviations has not been maintained, or the recorded deviations are excessive; or
  • deemed necessary by the master for the safety of navigation, and no less often than every two years; every dry docking or after significant structural work.
For “regulated Australian vessels” there is no minimum statutory period when a compass should be adjusted provided deviation on all headings is less than 5 degrees, compass deviation book is maintained and the compass is kept in good condition.

Magnetism of a new ship can be particularly unstable. Therefore, the performance of a magnetic compass should be monitored carefully during the early life of the ship, and adjustments made if necessary. To ensure a compass is in good working condition, it is important to check performance of magnetic compasses particularly after:
  • carrying cargoes which have magnetic properties;
  • using electromagnetic lifting appliances to load or discharge cargo;
  • a vessel has been in a casualty where it has been subject to severe contact or electrical charges;
  • a vessel has been operating on short voyages for a long period of time then relocates, which results in a large change in magnetic latitude; or
  • a vessel has been laid up or has been lying idle. Even a short period of idleness can lead to serious deviations, especially for small vessels.