Ships usually have a compass onboard to help the ship’s navigators to ascertain their direction of travel while at sea. In addition to a compass, ships also carry other navigational equipment that aids them in staying on course. This equipment is usually mounted inside, or on, what is called a binnacle, for ease of use and convenience. Standing approximately waist high, navigational equipment is mounted to, or encased, in the binnacle, which is usually located on the deck of the ship in front of the helmsman. Aside from serving as convenience for the ship’s crew to access the navigational instruments, binnacles also help protect the instruments from damage.
Originally intended to house the ship’s compass, the binnacle has gimbals in which the compass is mounted. Doing so keeps the compass level as the ship rides up and down with the waves. Aside from the compass, the binnacle usually has other sections built into it and often houses other equipment. This equipment may include a light source, such as an oil lamp, additional compasses and timers to help estimate speed. All this equipment is considered essential for ship navigation, in particular the light source, which is meant to illuminate the compass face to aid navigation at night.
Magnetic force is a major concern with ship operators, because the ship itself acts like one big magnet. Therefore, the ship will adversely impact the accuracy of a magnetic compass. To compensate for this, ships will usually employ one of two methods: Kelvin Balls or Flinders Rod. Kelvin's Balls are two iron balls usually mounted on each side of the binnacle, while Flinder's Rod are two small rods suspended on each side of the structure. These smaller magnets help to compensate for the inaccuracy caused by the ships own magnetic force through introducing a counter-active magnetic force.
Additionally, the term binnacle list is a common term used on ships. Used to excuse those who are sick from duty, the list will provide all relevant details of the individuals listed on it for accountability purposes. Prepared by the senior medical officer on the ship, the report is usually handed to the ship's commanding officer, and traditionally he or she laid it on the binnacle for ease of access. Thereafter, upon review, the commanding officer usually approves the report before storing it. Once approved, no other crew members can be added to the list without approval from the commanding officer.