Compass Check with pre-calculated Azimuth Angles

by Erik De Man

With the data contained in the manuals used for Celestial Navigation, it is also a trivial matter to check the compass with the calculated bearing to some celestial body, even well away from any land marks and in a strong unknown current.

 It is not possible to do this with GPS, nor any other instrumentation on board. The only way to truly check the compass at sea is with celestial techniques.

The technique is derived from the Rise and Set Times of celestial objects. From the Sight Reduction Tables not only the LHA at local rise or set time is determined but also the Azimuth for the appropriate object. The Azimuth can be easily translated in a bearing to this object. At the moment of rising or setting, the ships (true) course can be changed such that the vessel heads exactly to the object on the horizon. The true course and the course read from the compass can be compared and corrected.