Page 725 the smooth sheet 7737 



7737. Vertical Casts 



In conjunction with echo sounding, occasional comparisons are made with vertical 

 casts taken by the leadline or wire method. Such simultaneous soundings are both 

 to be placed on the smooth sheet, in pencil; the echo sounding at the correct position 

 and the vertical cast immediately beneath it and connected to it by means of a bracket. 



After verification in the Washington Office, only the echo soundings shall be inked 

 in areas of comparatively regular bottom. Where vertical-cast comparisons occur in 

 areas of steep slopes or very irregular bottom, both the echo sounding and the vertical 

 cast are inked, the latter bemg marked "VC". 



774. Errors in Soundings and Positions 



During the plotting of the soundings and the delineation of the depth curves, 

 the smooth-sheet plotter must be ever alert to detect errors in the Sounding Records, 

 whether in the original entries or in the final reduced depths. In spacing the sound- 

 ings with the spacing dividers, previously undiscovered errors in the plotted positions 

 may often be disclosed, which may have resulted from origmal erroneous or inadequate 

 data, or from errors made by the plotter. As the soundings are penciled, errors 

 in the depths may be disclosed by the fact that the soundings on adjacent lines are not 

 consistent, or by the fact that when the depth curves are drawn they are forced into 

 representations of unnatural bottom features. 



If errors are discovered or suspected, they must be verified and corrected wher- 

 ever necessary. But no deviation from the original recorded data shall be made 

 unless this appears reasonable and is supported by other evidence. Where any entry 

 in the Record is amended or rejected, such changes shall be made in colored pencil 

 (see 7741) and each change fully explained or justified by a note in colored pencil in 

 the "Remarks" column. 



Two general classes of errors may occur in the Sounding Records; those which 

 affect the positions of the soundings and those which affect the depths. And of these 

 two classes certain types of errors will affect only isolated soundings or positions, while 

 others will affect an entire area. The latter, of course, are the most difficult to discover. 



In 7624A, there have been listed the kinds of errors found occasionally in the 

 recorded position data which affect the positions of the soundings on the smooth sheet. 

 Errors of position may also result from the following sources: 



(a) Faulty spacing of the soundings along the sounding line, due to — 



(1) An error in plotting the soundings. 



(2) A failure to take into account variations in course or speed in plotting the soundings. 

 (6) One of the sextants badly out of adjustment. 



(c) One or more of the control stations incorrectly plotted. 



(d) In R.A.R. control, the use of an erroneous horizontal velocity of sound for one or more of 

 the distances. (See also 7636.) 



(e) Small clock errors. 



(/) An omission of variations in course or speed in the Sounding Record. 



Erroneous soundings may result from an almost infinite variety of causes, of which 

 the following are the more common: 



(o) A confusion of numbers in the Sounding Records, such as the interchange of 7 and 11 or 15 

 and 50, where the soundings obtained are transmitted orally to the recorder (see 4623) . 



(b) A misread sounding; that is, the leadsman or fathometer attendant actually reports a sound- 

 ing different from that obtained. 



