Degaussing systems on board marine vessels

What is Degaussing?

The ship’s hull, made of steel, acts like a large floating magnet surrounded by an even larger magnetic field. When the ship moves through the water, the magnetic field moves along with it and produces disturbance in the earth’s magnetic field. This distortion effect on the earth’s magnetic field can easily be detected by the devices designed to track such distortions. The degaussing system is used to reduce the ship’s effect on the earth’s magnetic field by preventing the generation of the magnetic disturbances.

The application of degaussing system started during the world war II to prevent the naval ships from magnetic mines and torpedoes. When the ship used to come near a magnetic mine or a magnetic torpedo,the magnetic field of the ship used to actuate the firing mechanism and cause the mine or torpedo explode. Thus, degaussing systems were installed to counteract the ship’s magnetic field by cancelling the changes in earth’s field around the hull of the ship.

ship's permanet magnetism

Ship in Earth’s Magnetic Field.

Technically speaking, earth is nothing but a dipole magnet. A magnet with its magnetic lines flowing from north to south. These magnetic lines of force at the earth’s surface have two two main components:

  • Vertical components
  • Horizontal components

The horizontal components is further divided into two main components:

  • Longitudinal
  • Athwart ship

When the ship with its magnetic field moves along these various magnetic lines, the permeability of ship changes, which in turn affects its field strength. Moreover it is a known fact that metal is more permeable that water or air. Thus, as the field intensity of the ship increases, the disturbance in the magnetic field around the ship increases.

Understanding the Ship’s Magnetic Field.

Permanent Magnetization

When a ship is built under the influence of a ship’s magnetic field, it becomes permanently magnetized. This permanent magnetic property of the ship plays a vital role in the degaussing process.

The magnitude of this magnetic field depends on three things:

  • The intensity of the earth’s field where the ship was built
  • The orientation of ship when built
  • The material of the ship

It is to note that the permanent magnetic field of the ship is not affected by the latitude, heading or pitch of the ship.

Induced Magnetization

This type of magnetization is caused due to the presence of the ship’s magnetic material in the earth’s magnetic field.

This type of magnetic field depends on two things:

  • The strength of earth’s magnetic field
  • The orientation of ship

It is to note that the components of this magnetic field – Longitudinal, athwart ship and vertical , are affected by latitude, heading and rolling-pitching of the ship.

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