What is the cause of deviation in navigational terms?

Deviation in navigational terms refers specifically to the magnetic influence that arises from the vessel itself, specifically its hull and any magnetic materials on board. This phenomenon affects how the ship’s magnetic compass reads direction compared to true magnetic north.

When a ship is equipped with metal components, equipment, or even electrical systems, these can distort the Earth’s magnetic field in the vicinity of the compass, leading to discrepancies in the compass readings. This deviation must be corrected to ensure accurate navigation.

The other options describe different navigational concepts or phenomena but do not pertain to the internal influences of the vessel on the compass. Friction from motion may affect the ship's handling but does not contribute to magnetic deviation. The angular difference between true and magnetic bearings relates to variation, not deviation. Electromagnetic interference from satellites deals with modern navigation systems and not the magnetic influences caused by the ship itself. Thus, understanding that deviation is specifically caused by the ship's own magnetic properties provides clarity on this key navigational concept.