Deperming is a process to neutralize the magnetic field by a vessel to eliminate the danger of magnetic influence sea mines. Heavy gauge copper cables are wrapping around the hull of vessel and electric cables to run in a high currents (as high as 4000 amperes) until the ship has a negative polarity. This procedure is intended to prevents the ship affected a sea mines attack. The cables are wrapped vertically around the ship, when energized, the ship permanent magnetism will be reduce and this procedure will helping to protect it from magnetic sea mines.
Before the vessel through the deperming process, its should to measure first in a several times. The vessel will be wrapping by coils in the bottom are counter acting the Earth Magnetic field so the ship is in "Zero". Then the wrapping coils run first high + current then same. This step should do in a many times till the magnetic range reach "Zero". Switch off the sea bottom coils which puts the vessel in normal Earth Magnetic Field again. The magnetometer are to monitor the deperming process.