Principles of naval engineering - Historic Naval Ships Association

PRINCIPLES OF NAVAL ENGINEERINGstages of amplification, and drives the servomotor.DEGAUSSING INSTALLATIONSA ship is a magnet because of the presenceof magnetic material in its hull and machinery.A ship is therefore surrounded by a magneticfield which is strong near the ship and weak at aconsiderable distance from the ship. As a shippasses over a point on the surface of the earth,the magnetic field of the ship is superimposedupon the magnetic field of the earth, thus tendingto distort the earth's field around the ship. Ifthe ship is close to a magnetic mine or torpedo,the distortion caused by the ship's field willactivate the firing mechanism to detonate themine or torpedo.Degaussing equipment is installed aboardship to neutralize the disturbance of the earth'smagnetic field caused by the ship, and thus toreduce the possibility of detonating a magneticmine or torpedo. A shipboard degaussing installationconsists of one or more coils of electriccable in specific locations inside the ship's hull,a d-c power source to energize these coils, anda means of controlling the magnitude and polarityof the current through the coils. Compasscompensatingequipment, consisting of compensatingcoils and control boxes, is also installedas a part of the degaussing system, to compensatefor the deviation effect of the degaussingcoils on the ship's magnetic compasses.Naval ships are tested periodically at magneticrange stations to determine the configurationof the ship's magnetic field. SensitiverOUTPUT CONTROLLEROUTPUT