The binnacle houses one of the most important navigational instruments on the boat: the nautical compass. The compass shows the magnetic north like a standard compass, and provides a reference for navigation.
Nonetheless, in order to be certain that they are following the correct course, sailors combine the compass reading with the interpretation of other elements, such as the nautical chart or the direction indicator or the angle of the rudder.
This compass, which must always be within the helmsperson’s sight, is protected from the weather, enclosed in a case called a binnacle.
From a certain point on, boats began to use a lot of metallic elements that caused the magnetic needle to function erratically; in order to correct this, a soft iron ball (a steel alloy with 0.30% or 0.40% carbon) was placed on either side of the binnacle, eliminating the magnetism around it and making the compass to be effective again. The balls are: green on the starboard side (the right-hand side of the boat) and red on the port side (the left side).