Deviation of compass readings is based on which vessel characteristic?

Deviation of compass readings is primarily influenced by the vessel's heading. The heading indicates the direction in which the vessel's bow is pointing, and it plays a critical role in how magnetic fields interact with the ship's compass. As a vessel changes its heading, the magnetic materials on board, such as engines, electronics, and even metal structures, can distort the magnetic field, leading to variation in compass readings. This phenomenon is known as magnetic deviation, where the compass shows a false direction due to these onboard influences.

The other characteristics—speed, location, and draft—do not directly impact the compass deviations in the same way. Speed may affect the hydrodynamics of the vessel and its motion through the water, but it does not alter the magnetic forces affecting the compass. Similarly, location may play a role in understanding variations in magnetic fields across different geographical areas, but it does not directly affect the compass readings as a function of the vessel's characteristics. Draft, which refers to the vertical distance between the waterline and the bottom of the hull, influences the vessel's stability and buoyancy rather than its magnetic properties. Thus, heading is the key factor in determining compass deviation.