Page 523 echo sounding 5554 



If the corrected stop watch time differs from 10 minutes, the frequency of the reed 



is incorrect and the 



, r-600 

 Correction (m percent) = — Tf, — 



600 

 and Vi = V-rjT 



where T equals the actual time (in seconds) for the 205 transmitted signals, V equals 

 the velocity of sound for which the instrument is calibrated, and Vi equals the velocity 

 of sound for which the instrument is actually operating during the test. 



For instruments calibrated for a velocity of sound of 800 fathoms per second the 

 procedure is the same, except that 200 transmitted signals should be counted instead 

 of 205. 



5554. Verification and Adjustment of 808 Fathometer 



The reed tachometer of the 808 Fathometer is identical with that of the 312 

 Fathometer. It also shall be removed from the instrument once a year and forwarded 

 to the Washington Office for calibration. And during the field season its frequency shall 

 be verified at least once a month and the results recorded in the Sounding Records. 

 The purpose of the monthly check is not to determine the exact frequency of the middle 

 reed but to discover if a change of frequency has occurred. 



At correct motor speed, the travel speed of the fathogram under the stylus is 

 exactly 2 inches per minute, so an approximate verification may be made by measur- 

 ing the length of paper that moves under the stylus in a given time while the middle 

 reed is vibrating at maximum amplitude. The instrument should be operated for a 

 half-hour at slow speed, after which it should be changed to fast speed for the test. 

 The motor speed should be adjusted and maintained during the test so that the middle 

 reed vibrates continuously at maximum amplitude. A stop watch, whose rate has been 

 verified, is started simultaneously with the pressing of the fix-marker button. At the 

 end of exactly 4 minutes by the stop watch the fix-marker button is again pressed. If 

 the frequency of the middle reed is correct, the measured distance between the two fix 

 marks should be exactly 8 inches. The measurement should be made between the 

 right edges of the marks at the center of the fathogram and by means of a graduated 

 scale — not by the printed scale on the fathogram. A difference of 0.1 inch from 8 

 inches will indicate a deviation of 1}^ percent from calibrated frequency. If there is 

 any question as to the validity of the result, the test should be repeated several times. 

 Should these tests indicate a change in the frequency of the reed, follow the instructions 

 in 5553 for the 312 Fathometer until the tachometer can be readjusted. (See also 

 5233 and 5238(g).) 



5555. Verification and Adjustment of Veslekari 



A check of the Veslekari motor speed should be made before each day's operations, 

 and this fact should be noted on the fathogram. The motor speed of the Veslekari 

 echo-sounding instrument is adjusted by the manufacturer for a calibration velocity of 

 sound of 800 fathoms per second. A velocity of sound of 820 fathoms per second is 

 more nearly average for the waters surveyed by the Coast and Geodetic Survey, and 

 since most of the other instruments used are so calibrated and adjusted, the motor speed 

 of the Veslekari should be altered to correspond to a calibration velocity of 820 fathoms 



