A DOCTOR OF COMPASSES

Evening Star, Issue 22447, 18 September 1936, Page 10

A DOCTOR OF COMPASSES

NAVIGATION COMPLEXITIES Ocean travellers on a great modern liner, comfortable in the knowledge that iron and steel provide security against the hazards of the deep, rarely give thought to the complications which modern ship construction has introduced into the science of navigation, says an exchange. But usually, when an ocean liner or coastwise steamer heads out of New York Harbour, a man is aboard whose thoughts are directed towards those very complications. Ho is the compass adjuster, and his is the task of discovering and correcting any irregularities caused by the ship’s iron and steel in that delicate and highly-sensitive instrument which, despite the development of the radio-coinpass and the gyrocompass, remains indispensable to navigation—the magnetic compass. The magnetism of a modern steamship, physicists point out, is due partly to the “ permanent ” magnetism of hard iron in the ship’s hull, partly to the “ transient ” or induced magnetism of soft iron in beams, engines, boilers, stacks, masts, and other fittings. The magnetised needle of the compass is sensitive to both permanent and transient magnetism; adverse magnetic fields, which may develop with the turning of the ship’s head, change in geographical position, inclining of the vessel from side to side, or introduction of iron and steel into the cargo, cause what mariners know as compass “ deviation.” It is with deviation that the compass adjuster is concerned. Three or four nautical instrument houses in New York, known to shipping officials through long and efficient service, do most of the compass adjusting in this vicinity. One or two members of each firm, usually after long apprenticeship, carry on this difficult work. Theoretical knowledge as well as practical seamanship are necessary qualifications for the job; the adjuster must be familiar not only with landmarks and local conditions, but he must be as adept as any ship’s captain in directing a ship. In locating disturbing magnetic forces the adjuster uses small magnetic deflectors, frequently devised by himself. Both in the use of deflectors and in the application of corrective or “ compensating ” magnets, nautical firms of high standing follow procedures which long experience has proved effective. J. C. Negus, member of a nautical firm which has been in business in New York for almost a centurj', points out that each adjuster has certain peculiar and often secret methods of his own. In compensating the compass for the adverse magnetic fields of the ship’s iron and steel, small bars of magnetised steel, usually made and seasoned by the adjusters themselves, are used. These bars are placed in racks in the binnacle chamber beneath the compass, some of them to neutralise or “ kill ” magnetic disturbances in horizontal iron, others to overcome similar disturbances traceable to vertical iron. During the ship’s construction large soft iron spheres are placed on the starboard and port sides of the binnacle to help to balance the ship’s mag netism, and a vertical iron bar, known as Flinder’s Bar, after its inventor, is always placed near the compass for the same purpose. But a vigilant eye must be kept on the compass to detect the deviations which are bound to arise in spite of these precautions. The adjuster usually sails with the vessel from its pier. Like a physician,* he is on call night or day, and he can perform his duties in any weather fit for sailing. If the vessel is small and if harbour traffic is not too heavy, he may complete his job before the boat is out of the harbour. In that case he catches a lift hack from a pilot boat or a fishing smack.