The stand on which a compass is mounted, and a piece of maritime history
The compass is such a vital part of the safe navigation of a ship that it is traditionally mounted on the bridge on the longitudinal center line directly in front of the helm. The stand on which the compass is placed is called the binnacle. Early binnacles were constructed using iron nails, but these were found to cause errors with the magnetic compass, so later binnacles were built with non-magnetic materials. Deviation was a continuing problem, particularly as the amount of iron and steel in ships increased. Captain Matthew Flinders, Royal Navy, determined that erecting a vertical metal bar in front of the compass allowed adjustments to be made to minimize this effect. Those devices are still called Flinders bars in his honor. Later, Sir George Airy, the Astronomer Royal, discovered that the accuracy of the magnetic compass could be further improved by placing quadrantal spheres (large balls of soft iron) on either side of the compass. Both the Flinders bar and the quadrantal spheres, along with various adjustable magnets, for correcting the compass were naturally mounted on the binnacle. From the beginning, binnacles included a lighting source, so that the helmsman could read the compass at night. Early lighting was provided by a candle or an oil lamp, but now electric lights are universally utilized. Even though seldom utilized, all ships engaged on international voyages are required to be equipped with a properly adjusted standard magnetic compass, or other means, independent of any power supply, to determine the ship’s heading and display the reading at the main steering position. This magnetic compass is invariably mounted in a binnacle.