Page 461 , echo sounding 5222 



5222. Operation 



The revolving drum is the time measuring device on this Fathometer. An aux- 

 ihary keying shaft is driven through a 1 to 4 gear ratio from the drum shaft so that a 

 keying cycle occurs at every fourth revolution of the drum. Soundings in feet are there- 

 fore recorded at the rate of 615 per minute and in fathoms at 102.5 per minute for a 

 motor speed of 2,460 r. p. m. 



At the correct instant of each fourth revolution of the drum, the signal sender, to 

 which it is keyed, sends an electric impulse to the transmitting oscillator, causing the 

 magnetostrictive unit to transmit a supersonic signal of a frequency of 14250 cycles per 

 second. The echo is received on the receiving oscillator and amplified by the echo 

 amplifier, the resulting current passing to the printer blade and through the record 

 paper at the point where the blade is in contact with the helical wire on the revolving 

 drum, leaving a permanent black mark on the paper. The arrangement of the wire on 

 the drum is such that at any instant the printer blade can be in contact with the helical 

 wire at one point only, and the revolution of the drum thus becomes a measure of the 

 elapsed time between the transmission and reception of the sound signal. 



a. Draft adjustment. — The adjustment for the depth of the oscillators below the surface of the 

 water is made with reference to a scale with a range from plus 10 to minus 5 feet. The adjustment for 

 draft must always be made on the to 10 part of the scale. Any adjustments made with reference to 

 this scale in feet are correctly applied to the fathogram irrespective of whether the soundings are 

 recorded in feet or fathoms. When the adjustment is set at zero, the instant of transmission coincides 

 with the zero of the record paper, but the recorded depths are all referred to the plane of the oscillators. 

 When the adjustment is set on the to 10 part of the scale, the instant of transmission is delayed to 

 account for the draft of the oscillators. 



The draft adjustment scale can also be used for mechanically applying other various corrections 

 involved in echo sounding, such as instrumental error (552), settlement and squat (553), and, under 

 certain conditions, tide (56). 



b. Motor speed adjustment. — The speed of the driving motor is controlled by a centrifugal governor 

 which can be manually adjusted by turning a knob on the end of the case. 



A meter calibrated in motor revolutions per minute and also a reed tachometer (see 5234) are 

 provided for verifying the motor speed. The middle reed of the tachometer vibrates at maximum 

 amplitude when the motor speed is 2,460 r. p. m., which corresponds to a velocity of sound in water of 

 820 fathoms per second. The reed tachometer is more accurate than the meter. The instrument will 

 accommodate a velocity of sound range from 760 to 880 fathoms per second. 



Since the calibration velocity of an echo-sounding instrument is a function of the motor speed 

 (see 555), the instrum3nt can be adjusted, under certain conditions, to record soundings based on the 

 actual velocity of sound in the area. 



A book is provided which contains instructions relative to maintenance, service, 

 operating difficulties, circuit tests, and tables of correct voltages and resistances, and 

 lists spare parts by number. 



5223. Comparison With 808 Fathometer 



The followmg are, in summary, the outstanding features of the Simplex-Bludworth 

 Fathometer that are not possessed by the 808 Fathometer: 



(1) A draft adjustment scale. 



(2) An indication of driving motor speed so that adjustments may be made to 

 account for the actual velocity of sound at the time of making the survey. 



(3) The record is made along a straight-edged stationary bar giving a straight 

 line record on paper with rectangular coordinates, eliminating contraction of the scale 

 near the paper edges. 



