ANSWERS TO PROBLEMS 



141 



(27) True. Induction in the Flinders bar from the degaussing coil fields will 



change as the Flinders bar is changed, and will therefore change the 

 errors from degaussing. Naturally, any compensating coil installa- 

 tion should be recompensated with change in the Flinders bar 

 length. 



(28) False. The ship should expect an easterly C error. 



(29) True. At the equator the fore-and-aft magnets are adjusted. However, 



the Flinders bar must also be adjusted either at the equator or on 

 the return trip to New York. (See ch. VIII.) 



ANSWERS TO PROBLEM 6 



The deviation curve recorded at New York contained the following coeflBcients : 



^ = 0.8° E. D = 0.0° 



B=1.0°E. £^=0.5° E. 



C=0.0° 



The deviation curve recorded at the Panama Canal Zone contained the follow- 

 ing coefficients: 



^ = 0.8° E. 

 S=9.0° E. 

 C=0.0° 



D=0.0° 

 ^=0.5° E. 



It will be noted that the only coefficient which changed during the voyage 

 from New York to the Canal Zone was the B coefficient — a change of 8° easterly. 

 Should an examination of the ship's history show that nothing had been done on 

 this voyage to change the permanent magnetism of the ship, then the change 

 in the B coefficient may reasonably be attributed to improper Flinders bar correc- 

 tion. The necessary amount of Flinders bar is calculated by means of the 

 formula given in chapter VIII. The B coefficients of deviation used in this form- 

 ula are taken from the data obtained on magnetic headings. Inasmuch as the 

 data available in this problem was taken on compass headings the Napier's dia- 

 gram must be used to convert to the equivalent B deviations on magnetic headings. 

 In this problem the difference between the deviations on B./W. compass headings 

 and the deviations on E./W. magnetic headings proves to be negligible. 



It is pointed out that none of the correctors, permanent or induced (including 

 the heeling magnet), should be moved while on the voyage from New York to 

 the Canal Zone or the results for purposes of Flinders bar calculation will not 

 be reliable. For a further discussion of the conditions under which to take 

 deviation curves for determining the length of Flinders bar, see chapter VIII. 

 Assume X (shielding) to be 0.8 of unity. 



Hi = Q.nQ (at New York^. 

 Zi = 0.539 (at New York). 

 Bi = 1.0° E. {B coefficient at New York). 

 //2= 0.311 (at Canal Zone). 

 Z2 = 0.260 (at Canal Zone). 

 ^2 = 9.0° E {B coefficient at Canal Zone). 

 or 0.170X0.0175-0.31lX0.1584 "| 

 0.539-0.260 J 



^ " 0.0030-0.0493 1 



= 0.8 



0.279 

 0.0463 "! 

 0.279 J 



r 0.0370 "| 



[^ 



279 J 



0.133 



