4313 HYDROGRAPHIC MANUAL PaGE 332 



Leadlines not in use should be coiled and stowed. All markings should be examined 

 and necessary repairs made at once. 



4313. Care of Instruments 



Instruments are precision mechanisms, delicately balanced and accurately marked. 

 One bearing or pivot allowed to deteriorate or freeze destroys the accuracy of any 

 observation. For this reason proper and unremitting care is absolutely essential. 

 Every individual using an instrument must realize that the accuracy required in survey- 

 ing cannot be secured without this care. 



The arc of a sextant or protractor may be cleaned by wiping lightly with a chamois 

 skin or soft rag dipped in a weak solution of ammonia. It must never be polished 

 with sandpaper, emery cloth, a rubber eraser, or any other type of abrasive, as the use 

 of such materials will scratch metal and eventually deface the graduations. Alcohol, 

 gasoline, or kerosene should never be used to clean arcs of instruments, as their use will 

 remove the filler from the graduations. 



Alcohol, gasoline, and kerosene leave an object extremely dry after evaporation. 

 When they have to be used to remove an excess of oil or grease in the bearings or 

 between bearing surfaces of any instrument, the instrument must not be stowed away 

 until these surfaces have been given a light coating of oil after all the cleaner has 

 evaporated. 



All instruments should be carefully dried after exposure to water or dampness, 

 oiled where necessary, and any oil cups refilled. Special attention should be given to 

 lenses and sextant mirrors to ensure that they are thoroughly dried. 



Lenses and mirrors may be dusted with a camel's hair brush, or cleaned by gentle 

 rubbing with soft tissue paper or lintproof cloth, after being slightly moistened with 

 the breath. A lens should be examined occasionally to see that it is tight in its cell. 



TafFrail logs and current meters are similar in that both have rotating parts con- 

 stantly exposed to salt water. After use, both should be thoroughly dried, well oiled, 

 given enough turns by hand so that the new oil will have a chance to lubricate all 

 moving parts, and then all oil chambers should be refilled. 



4314. Repairs to Equipment and Instruments 



So far as possible all equipment shall be maintained in the best working condition 

 by the personnel aboard the vessel. Repairs are to be performed only by experienced 

 and competent technicians. Extensive repairs to heavy equipment, particularly 

 machine work, should be let on contract with firms specializing in the particular type 

 of work. Complicated equipment like the gyrocompass, except for minor details, 

 shall be repaired only by experts representing the manufacturer. 



During lay-up or repair periods between assignments, the equipment shall be over- 

 hauled and put in the best possible condition in order to reduce repairs and maintenance 

 in the field to a minimum. 



Expenditures for repairs to survey instruments shall not be incurred in the field, 

 except where local costs are less than shipping charges to the Washington Office, or in 

 emergencies. Many minor repairs can be made by officers themselves. In emergencies, 

 when the time required to send an instrument to the Washington Office for repairs, or 

 to requisition a replacement, would delay field operations, instruments may be repaired 

 locally. In such a case the voucher for payment must be accompanied by a detailed 

 justification of the action. 



