Use of degaussing coils on a ship


The previous article described how magnetic field of the ship creates disturbance in the earth’s magnetic lines. Degaussing of ship is the method used to prevent this disturbance in the earth’s magnetic field caused due to the change in a ship’s magnetic field. Let’s take a look at the various methods used for degaussing a ship.

The Degaussing System

Degaussing of ship is also known as "making the ship invisible", i.e to make ships invisible to a magnetic field. A degaussing system consists of permanently installed degaussing coils on the shipboard. Degaussing takes place by controlling the flow of electric current though these coil.

The main components of a degaussing system are :

  • Degaussing coils
  • Controller
  • Degaussing folder
  • Power source
  • Compass compensating equipment.

A control unit is used to control the current through these coils.The system also consists of a compass compensating equipment which is used to prevent any kind of disturbances to the magnetic compass by the magnetic field generated by the degaussing coils.

Types of Degaussing Methods

There are various types of degaussing systems used on board today. The main difference between these types, is the amount of power supplied and the arrangement of coil circuitry. This means that the various types of methods of degaussing used on board differs in the arrangement of the degaussing coils and the amount of power supplied.

The magnetic lines generated by the ship’s permanent or induced magnetic field, plays an important role in the degaussing process. These magnetic lines of force are acted upon in different ways to nullify their effect on the earth’s magnetic field. The various types of coil arrangements used are as follows :

Main Coil (M)

In this type, the coil is installed in a horizontal plane at the waterline. When current is passed, the coil compensates the induced and permanent vertical components of the ship’s magnetic field. When the ship changes the hemisphere , the coil polarity is to be manually adjusted.

main coil

Forecastle Permanent – Quaterdeck permanent Coils (FP-QP)

This type of coil compensates for the longitudinal permanent components of the ship’s magnetic field.The FP coil is installed horizontally at forward of the ship and encircles approximately one-third of the ship at the main deck., while QP encircles one-third of the aft region of the ship.


Forecastle Induced – Quaterdeck Induced Coils (FI-QI)

The location of these coils is almost same as that of FP and QP, but they compensate for the longitudinal magnetic components of the ship’s magnetic field. The polarization is automatically changed by converting a gyro input signal to a magnetic heading. The current in the coil is directly proportional to the earth’s magnetic field.


Athwartship Coil ( A)

This coil is installed in the vertical position and compensates the athwartship’s permanent and induced components of the ship’s magnetic field.



The Federation of American Scientists (FAS) Website