136 HANDBOOK OF MAGNETIC COMPASS 



(ft) Improper sphere correction. 



(c) Improper Flinders bar correction. 



9. Should the value of D change with latitude it is because — 



(a) Spheres are magnetized. 



(6) Induction in the spheres by the compass needles. 



(c) Spheres are too far out from the compass and have no effect. 



10. If the Flinders bar length is doubled — 



(o) It must be inverted. 



(6) It will necessitate changing the position of the heeling magnet. 



(c) Sphere correction should also be revised. 



PROBLEM 5 

 True — Dalse. (Also give one sentence comments.) 



1. A magnetically frozen compass reading 090° for all headings of the ship 

 would require fore-and-aft magnets in order to free it. 



2. The position of the heeling magnet, although once adjusted, should be 

 changed as required with latitude changes. 



3. Axiomatically enough, large spheres are always used on large ships and 

 small spheres on small ships. 



4. Although the degaussing compass compensating coils were not changed, If 

 the compass is readjusted magnetically, a new deviation curve must be taken for 

 both degaussed and undegaussed conditions of the ship. 



5. After a ship is depermed it will require more Flinders bar. 



6. If there is a Flinders bar in the binnacle a change in the heeling magnet 

 will probably change the error on an east heading. 



7. Heeling errors, due to roll, are most noticeable on north and south headings. 



8. A Napier's diagram is a device for determining the preper length of Flinders 

 bar. 



9. When swinging for a degaussing deviation curve, the degaussing coils must 

 all be energized at full value. 



10. If degaussing throws a compass off over 90° it cannot be corrected. 



11. If, upon securing the degaussing directly, the compass does not return to 

 normal, the coils must be recompensated. 



12. It is good practice to delay adjustment until three or four days after 

 deperming, if possible. 



13. A ship travelling on a north heading while practicing gunnery should expect 

 to acquire a westerly B error. 



14. If a compass has the same westerly err^r on all four intercardinal head- 

 ings it should have larger spheres. 



15. If a heeling coil adjustment for compass compensation is changed the B 

 coil correction will probably have to be corrected again. 



16. Flinders bar corrects for induced effects in horizontal soft iron due to 

 changes with latitude. 



17. A ship built on an east-west heading will probably have its maximum 

 deviations on north and south headings. 



18. A compass with westerly deviation on an east heading will require magnets 

 athwartship, red to port. 



19. In making a dockside setting of the compass compensating coils the de- 

 gaussing coils should be energized at maximum operating currents to insure 

 greatest accuracy of adjustment. 



