Relative Azimuth

Relative azimuth is a term used in marine satellite communications. It is the bearing (azimuth) to the satellite referenced from the bow of the vessel in a clockwise direction.

Relative Azimuth Calculation

The azimuth to the satellite does not change unless the vessel moves location and stays the same as the heading changes. The relative azimuth will change as the ship’s heading changes.
The relative azimuth is counted clockwise from the ship’s bow through 360 degrees and is set by the home flag sensor within the radome.
If the above decks radome is not exactly aligned with the bow, as is often the case, then the setting in the antenna controller (DAC) can be changed to compensate for the difference to align it with the bow. If this is not done then you may have problems finding the satellite as the antenna will be searching in the wrong part of the sky. The search window of a stabilised antenna is usually about 10° so therefore it will search ±5° of the calculated position of the satellite.
Also, relative azimuth is also used to check for blockages from the ship’s mast, exhausts, etc.

Example
You have calculated that the azimuth to the satellite at your current location is 315° and you’ve checked the gyro compass heading as 240°. Which means if you are stood on the bow the vessel the satellite will be 75° towards starboard.

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