Marine Navigation Instrument

A marine navigation instrument is a device built to let a ship's crew determine position, heading, depth or speed while out of sight of land, so a vessel can cross open water and reach port safely. The earliest instruments used the sky and the earth's magnetic field: the magnetic compass gave a steady heading, the astrolabe and later the sextant let a navigator measure the angle of the sun or stars above the horizon to fix latitude, and the marine chronometer, once accurate enough to keep true time at sea, finally let navigators calculate longitude as well, solving a problem that had cost ships and lives for centuries. Later instruments extended this same task with new physics: the gyrocompass gave a true north bearing unaffected by magnetic deviation, the echo sounder and chip log measured depth and speed through the water, and marine radar let a bridge crew detect coastlines and other vessels at a distance in poor visibility. Together these instruments make up the standard equipment a ship's bridge has carried, in one form or another, since long-distance sea travel began.