12 December 2001
Figure 5-16 Sample Shipyard Layout
A steel object under the magnetic forces of the earth will itself become
polarized and set up a magnetic field of its own. A steel-hulled ship will become a huge
floating magnet itself. In addition, there are induced magnetic signatures caused by
inside electronics and motors. This magnetic field makes the ship vulnerable to
magnetically sensitive mines or other magnetic influence detecting devices.
The science of degaussing deals with reducing the ship's magnetic field,
or signature. Normal deperming techniques based on alternate reversals of ship
polarity are used to reduce the ship's permanent structural hull signature whereas
equipment induced signatures are controlled by interior degaussing cables. In order to
determine the characteristics of a ship's magnetic field it is necessary to make periodic
measurements of the field, referred to as "ranging". The primary type of
degaussing/magnetic silencer range consists of a linear pattern of instrumentation
tubes containing magnetometers embedded in the channel bottom.