CHAPTER XI. DEGAUSSING COMPASS COMPENSATION 

 A. General Principles 



111. Degaussing effects. — The degaussing of ships for protection 

 against magnetic mines has created additional effects upon magnetic 

 compasses which are somewhat different from the permanent and in- 

 duced magnetic effects usually encountered. These effects may be 

 considered as electro-magnetic effects which depend upon : 



(1) Number and type degaussing coils installed. 



(2) Magnetic strength and polarity of the degaussing coils. 



(3) Relative location of the different degaussing coils with 

 respect to the binnacle. 



(4) Presence of masses of steel which would tend to concen- 

 trate or distort magnetic fields in the vicinity of the binnacle. 



(5) The fact that degaussing coils are operated intermit- 

 tently, with variable current values, and with different polarities 

 as dictated by necessary degaussing conditions. 



112. The magnetic fields at the binnacle must be considered sep- 

 arately for each degaussing coil. The magnetic field from any indi- 

 vidual degaussing coil will vary proportionately with the excitation of 

 the coil, and its direction will completely reverse with changes in the 

 coil polarity. 



Uncompensated degaussing coil effects create deviations of the 

 compass card and conditions of sluggishness and unsteadiness which 

 are similar to, and generally larger than, the effects of normal ship's 

 magnetism on the magnetic compass. 



113. Degaussing compensation, — The fundamental principle of 

 compass com^pensation is to create magnetic fields at the compass 

 which are at all times equal and opposite to the magnetic effects of 

 the degaussing system. Creation of such magnetic fields is accom- 

 plished by appropriate arrangements of electrical coils about the 

 binnacle. To do this completely, it is necessary to arrange coils about 

 the binnacle for each effective degaussing circuit such that they create 

 their opposing effect either directly or by a combination of com- 



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