Gyrocompass

This article is about devices used on ships. For the type of gyroscope used to determine aircraft heading, see Heading indicator.

Cutaway of an Anschütz gyrocompass

A gyrocompass repeater

A gyrocompass or Gyrocompassing is a type of non-magnetic compass which is based on a fast-spinning disc and the rotation of the Earth (or another planetary body if used elsewhere in the universe) to find geographical direction automatically. A gyrocompass makes use of one of the seven fundamental ways to determine the heading of a vehicle. A gyroscope is an essential component of a gyrocompass, but they are different devices; a gyrocompass is built to use the effect of gyroscopic precession, which is a distinctive aspect of the general gyroscopic effect. Gyrocompasses, such as the fibre optic gyrocompass are widely used to provide a heading for navigation on ships. This is because they have two significant advantages over magnetic compasses:

• they find true north as determined by the axis of the Earth's rotation, which is different from, and navigationally more useful than, magnetic north, and
• they have a greater degree of accuracy because they are unaffected by ferromagnetic materials, such as in a ship's steel hull, which distort the magnetic field.

Furthermore, new generation fibre optic gyrocompasses can also help protect ships from potentially faulty GPS positions caused by GNSS jamming and spoofing, as FOG compasses can calculate their own position with reference to previously verified data.

Aircraft commonly use gyroscopic instruments (but not a gyrocompass) for navigation and attitude monitoring; for details, see flight instruments (specifically the heading indicator) and gyroscopic autopilot.