Page 519 echo sounding 5545 



desired direction to make the recorded depths read the desired values. This nut 

 should then be retightened and the instrument restarted, and another comparison 

 made. This operation should be repeated until the fathogram depths have the desired 

 relation to the measured depth. 



An instrumental comparison with the Dorsey Fathometer can be substituted for 

 the leadline comparison. The phasing dial of the Veslekari should be set on zero posi- 

 tion and the depth-selector and starting-frequency switches of the Dorsey Fathometer 

 on positions 1 and 4 respectively. The comparison should be made from the vessel 

 stopped in a calm sea over smooth level bottom in a depth between 20 and 40 fathoms. 

 If the depths registered on the two instruments do not agree within 0.3 fathom the 

 Veslekari should be adjusted to agree with the Dorsey Fathometer. This adjustment 

 is made as described above. 



5545. 808 Fathometer 



The index of the 808 Fathometer is adjusted by means of a knurled hand screw^ 

 marked "zero adjustment," on the hinged door of the cabinet. The hand screw serves 

 as a vernier adjustment to move the phasing dial by small amounts, and consequently 

 to change the time of the transmitted signal slightly with reference to the printed scale 

 of the fathogram. When the hand screw is turned so that the phasing dial moves 

 clockwise the scale value of the index is increased, and decreased when it is moved 

 counterclockwise. 



This instrument should be adjusted for instrumental error, draft, and settlement and 

 squat, by suspending a bar at a known depth (5 or 6 feet) below the bottom of the fish 

 and turning the hand screw until the recorded sounding, when corrected for settlement 

 and squat, equals the depth of the bar below the surface of the water. (See 557.) The 

 adjustment must be made with the phasing dial set on position A and the instrument 

 recording in feet. The gain control should be set at the value normally used during 

 surveying (between 7 and 10) and the correct motor speed must be maintained, as 

 indicated by the reed tachometer (5165c). After the index has once been adjusted by 

 bar check, it shall not be readjusted until another bar check is taken, even though the 

 recorded position of the transmitted signal may change. 



The 808 Fathometer may be operated to record depths either in feet or fathoms 

 and the times when the different units are to be used are specified in 3112. The change 

 from feet to fathoms is accomplished by a control which alters the speed of operation 

 of the instrument in the ratio of 6 to 1, but the recorded position of the transmitted 

 signal is not changed by this same ratio, as it should be for correct soundings. The 

 closing of the contacts, which produces the transmitted signal, occurs at the same 

 angular position of revolution with respect to the fathogram, being unaffected by the 

 change in speed of operation. Except for other electric or mechanical imperfections, 

 the following is an example of the error introduced. If the index has been adjusted 

 so that the transmitted signal records at 2 feet, and the speed of operation is changed 

 to the fathom scale, the transmitted signal will still record on the second division line, 

 but this will now be equivalent to 2 fathoms, thus introducing an error of 10 feet in the 

 recorded soundings. 



For recorded soundings all in feet, or part in feet and part in fathoms, the instru- 

 ment shall be adjusted with the instrument operating in feet, so that the recorded 

 position of the transmitted signal (in feet) is correct. And no change shall be made in 

 the adjustment for soundings recorded in fathoms. 



