In our previous posts we have discussed about degaussing and its process. However, a term ‘DEPERMING’ comes which is a way ahead for the degaussing process. When a ship is incapable to neutralise its permanent magnetism during normal degaussing process due to the extreme value of permanent longitudinal/athwartship magnetism or any magnetization or an uneven permanent vertical-magnetism, then the ship is placed for this Deperming method.
The main aim of this process is to decrease / nullify the permanent magnetism and bringing the ship to better standards. You can also say that Deperming process is a broad scale adaptation of demagnetisation of a ship. Moreover, Its hardly achieved a single time (or twice in some special case) in the entire service of the ship. Sometimes, when a large scale changes are carried out in ship’s structure, then also Deperming is required to be carried out. Before starting the process of deperming, it is necessary that every magnetic susceptible devices are taken out of ship. Deperming is carried out in specially designed bays which are also known as Deperming-bays.
During Deperming, The coil’s arrangement (under water and on ship’s structure) is such that whenever a DC current is passed through them, they generate a magnetic field which is same but in opposite direction to the ship’s permanent magnetism. This generated magnetic field counteracts the ship’s permanent magnetic field and nullifies it. This process is repeated again and again, and the readings of permanent magnetism onboard are taken out at different locations. The process is repeated till the time the magnetism in the ship’s structure becomes negligible.
This is one of best methods till to date to liquidize the effects of permanent magnetism on a ship’s body due to the influence of Earth’s magnetic field.