What causes compass deviation?

Compass deviation refers to the error introduced in a magnetic compass due to magnetic interference from nearby metallic objects and electrical equipment on a vessel. This interference can come from engines, generators, batteries, and other magnetic sources onboard. As a result, when a compass needle is affected by these magnetic fields, it may not point accurately towards true magnetic north, leading to deviation.

Understanding compass deviation is essential for navigation because it can lead to incorrect course plotting if not accounted for. Navigators often need to create a deviation table to correct for this error, ensuring more accurate readings and safe navigation. The other factors listed—water temperature, human error, and speed of the vessel—are not primary causes of compass deviation, highlighting the importance of recognizing magnetic interference as the main contributor to this navigational challenge.