THE SPERRY GYRO-COMPASS IN SERVICE. 

 By R. E. GiIvIvMOR, Esq., Associate. 



[Read at the twentieth general meeting of the Society of Naval Architects and Marine Engineers, held in 



New York, November 21 and 22, 1912. ] 



To be in service an instrument such as that with which the paper deals 

 must have passed the experimental stage — the stage of trial and develop- 

 ment. It must have emerged from that stage in a form which is fundamen- 

 tally sound and practicable. It must have demonstrated its value and have 

 been placed in actual service. 



That this has been accomplished is well proven by the fact that the 

 Sperry gyro-compass is now in service on six battleships and two submarines 

 of the United States Navy, and by the fact that the Bureau of Navigation 

 has awarded the same company a contract for ten additional complete 

 compass installations. 



The approximate, magnetic compass, with its many errors and weak- 

 nesses, is being superseded by an accurate instrument which gives us our 

 true course at sea, is unaffected by magnetic or physical forces tending to 

 deviate it, is simple and substantial, requiring little care or supervision. 



Mariners have so long depended on the magnetic compass that many of 

 them fail to realize the importance of the development of the gyro-compass. 

 An analysis of the present-day methods of navigation shows clearly that 

 ships using the magnetic compass do not steer the shortest course between 

 the points of departure and destination. The magnetic compass serves to 

 place them on approximately the correct course from point of departure 

 and serves to give the helmsman a means of holding to an approximate 

 average of this course. Because of the lag of the compass, it is necessary 

 for the helmsman to use more helm than really necessary; and because the 

 error of the compass is not exactly known, the ship is not held on the shortest 

 path between the points of departure and destination. From time to time 

 the position must be checked by observations and the course modified to 

 correct for variation from the correct course. A greater distance than 

 necessary is traversed because: (i) the helmsman is steering a serpentine 

 course, and (2) because the average course steered is not the correct course 

 and must be checked from time to time and modified to bring the ship to 

 her destination. The errors so introduced are small but on a long voyage 

 result in considerable loss of time and fuel. If observations of the sun or 



