What is a Magnetic Compass, its principle, types and errors?

Written by Amit Sharma

A compass is an instrument containing a freely suspended magnetic element which displays the direction of the horizontal component of the Earth’s magnetic field at the point of observation.


Magnetic compass is the most important of all instruments aboard even the most modern vessel and it is probably the most reliable. It’s origins go back as long ago as 2300 BC, but the Chinese development of the compass card dates to the 14th century and the sophisticated instrument we know today became stabilized with the advent of steel ships in the 19th century.

Magnetic compass is a primary means of navigation as a direction indicating device, of a ship.

  • It is the ships standard compass.
  • It is fitted above the bridge on the monkey Island at the centre line of the ship.
  • When reading output is needed to other bridge equipments, then a transmitting magnetic compass is fitted.

Points to pounder on magnetic compass:

The Magnetic Compass is the most familiar compass type. It functions as a pointer to “Magnetic North”, the local magnetic meridian, because the magnetized needle at its heart aligns itself with the horizontal component of the Earth’s magnetic field. The magnetic field exerts a torque on the needle, pulling one end or pole of the needle approximately toward the Earth’s North magnetic pole, and pulling the other toward the South Magnetic pole. The needle is mounted on a low-friction pivot point, in better compasses a jewel bearing, so it can turn easily. When the compass is held level, the needle turns until, after a few seconds to allow oscillations to die out, it settles into its equilibrium orientation.

The Principles of the compass

A Magnetic compass is a critical piece of marine navigational equipment. Simply put, a magnetised needle, suspended freely, points North because of the forces caused by the Earth’s magnetic field. Once North is known, the other directions are easily found.

The ship magnetic compass is usually housed on the ‘monkey island’ above the navigating bridge and reflected into the bridge by means of a periscope like device, so a helmsman can easily read the compass when he is steering the ship.

About the author

Amit Sharma

Graduated from M.E.R.I. Mumbai (Mumbai University), After a brief sailing founded this website with the idea to bring the maritime education online which must be free and available for all at all times and to find basic solutions that are of extreme importance to a seafarer by our innovative ideas.


Leave a Comment