What is the main use of a "binnacle" on a ship?

The primary function of a binnacle on a ship is to serve as a pedestal that houses a ship's compass. This essential navigational tool is mounted in the binnacle to ensure that it is secure and properly positioned for accurate readings. Additionally, the binnacle often incorporates features that protect the compass from magnetic interference and environmental factors, such as dampness, direct sunlight, and temperature variations.

This protective casing and strategic positioning facilitate reliable navigation for the vessel, making the binnacle a crucial component on a ship. The other options, while related to shipboard necessities, do not accurately describe the specific role of a binnacle. For instance, while navigational instruments might be stored on a ship, the binnacle is uniquely dedicated to the compass, making it distinct from general storage purposes for tools or emergency equipment.