Page 471 echo sounding 5237 



in feet. Both the vertical and horizontal representation are at a scale six times that 

 obtained when sounding at slow speed in fathoms. Where the bottom is very irregular, 

 with frequent and rapid changes in depth, the fathom scale should be used in depths 

 greater than 50 feet, thus avoiding the frequent changes of phase which would be 

 necessary on the scale in feet (see 3112(d)). On the fathom scale the changes of depth 

 are not so exaggerated and can usually be followed without difficulty. The possibility 

 of missing a pinnacle rock during a shift in phase is also eliminated. 



It is important that the sensitivity control always be kept at the highest value at 

 which the instriunent can be operated without introducing strays. The recorded value 

 for a given depth may be changed by as much as 2 feet in some cases by changing the 

 sensitivity control from one extreme to the other. This condition is inherent in all 

 echo-sounding instruments, but in any case the variation in time lag is less at liigher 

 values of echo-amplifier gain and by keeping the gain control near the maximum the 

 recorded soundings will more nearly approach the true depths. (See 5163.) 



To save time the fish should be left installed between successive days of hydrog- 

 raphy unless it is exposed to damage by so doing. For optimum operation of the 

 instrument, the magnetostrictive elements of the fish must be saturated with water. 

 If the fish, or if the launch and conseq\iently the fish, is removed from the water, these 

 elements dry out and must be soaked in water for a half-hour before use in sounding. 

 On one ship, where the launches were hoisted at night, the elements were kept saturated 

 by placing a watertight canvas sack, filled with water, around the fish so that it was 

 ready for use the instant the launch was lowered into the water. 



The fish should be examined periodically to determine whether any dirt or marine 

 growth has accumulated in the magnetostrictive-element housing. This inspection 

 can be made by removing the two diaphragms from the bottom of the fish. In cleaning 

 the elements, care should be taken not to injure the nickel laminations or the rubber- 

 covered wire. 



The recorder should be run for a warm-up period of 15 to 30 minutes before soimd- 

 ing or making a bar check (see 557) . It should be operated in the fathom position for 

 this purpose to conserve paper. This warm-up run may be made before the launch is 

 lowered, if it is expected that it will be wanted for sounding, or a bar check, immediately 

 after lowering. 



The following spare parts should be kept on hand for each instrument: (1) styluses; 

 (2) spare tubes, two each of types 1851, 1853, and 6F6; (3) brushes (for motors and 

 generators); (4) a governor; (5) fathogram paper. 



Major repairs should not be attempted while the instrument is in the launch, 

 except m emergencies. Excluding minor matters, repairs should be made only by quali- 

 fied persons. 



a. Lubrication. — Every 3 weeks the gear-box cover should be removed and the 

 gear train inspected to see if it is properly lubricated. If any gears appear dry "Singer 

 Motor Lubricant" or a good soft sodiimi-base cup grease should be applied lightly with 

 a smooth stick. 



Once each month the grease plug on each end of the driving motor should be re- 

 moved and a small amount of the same lubricant used in the gear box should be added. 



Every 2 months, or when the dynamotors show signs of binding, the grease plugs 

 should be removed and lubricated with one of the following lubricants: Master Lubri- 

 cants Company — Lubrico iVi6; or New York and New Jersey Lubricant Company — 

 F927 ; or Standard Oil Company— 6^5990. 



