What is the primary function of a compass on a vessel?

The primary function of a compass on a vessel is to determine the vessel's heading. A compass provides real-time directional information by indicating the vessel's orientation in relation to the Earth's magnetic field. Mariners rely on the compass to navigate effectively, especially when planning and following a course over water. This ability to ascertain the heading is crucial for safe navigation, as it allows the captain to make informed decisions regarding steering and course adjustments.

Other instruments and tools are typically used for different navigational purposes, such as calculating speed and distance or identifying nearby vessels, but these do not fall within the primary function of a compass. A compass does not measure water depth, nor does it directly aid in identifying other vessels nearby; those roles are fulfilled by other navigational equipment.