3432 HYDROGRAPHIC MANUAL PaGE 258 



Shorter intervals are desirable to obtain a more accurate delineation of irregular 

 submarine relief, as in channels or when crossing bars, reefs, and shoals. These inter- 

 vals should be uniform between consecutive positions when practicable, but in depths 

 of critical importance to navigation where the bottom is very irregular, the uniform 

 intervals should be abandoned and soundings taken as rapidly as accurate vertical 

 soundings can be obtained. When the uniform spacing is abandoned, the exact time 

 at which each sounding is obtained must be noted in the Sounding Record. 



3432. Frequency of Wire Soundings 



Intervals between vertical wire soundings, with the survey vessel stopped, should 

 not exceed one-half the distance between sounding lines. 



3433. Frequency of Echo Soundings 



In echo sounding, depths are measured continuously along each sounding line, 

 but when the echo-sounding instrument is of the visual type, there is no permanent 

 record of the profile except that provided by the recorded soundings in the vSounding 

 Record. The fathometer attendant shall observe the depths registered on a visual 

 instrument at all times and, except as provided in 3415, shall have no other duties 

 which will prevent this attention. 



Where the depths are uniform or the slope is uniform, the maximum interval 

 between recorded soundings shall be that which will provide soundings for the smooth 

 sheet in accordance with 7724. Wherever the depth varies more than 5 percent from 

 the uniform slope between the soundings at regular intervals, additional intermediate 

 soundings must be recorded at their exact times. 



In areas of irregular submarine relief, too much importance must not be attached 

 to the maintenance of a uniform interval. A uniform mterval facilitates the plotting 

 of the smooth sheet, but it is more important that the recorded soundings give a true 

 representation of the irregularities of the profile. In such areas the least depths of 

 all the irregularities must be recorded and between them the deepest depths, with as 

 many intermediate soundings as are required to define the profile accurately. At 

 least as many soundings must be recorded as can be shown on the smooth sheet (see 

 7724). Particular care shall be exercised to obtain and record at their proper times 

 all the critical soundings, such as the least depths on shoals or other elevations of the 

 bottom, and the maximum depths between these features and in troughs and valleys. 

 Soundings must also be recorded at each abrupt change of slope of the bottom. 



When echo soundings are obtained with a graphic recorder, a permanent record 

 of the profile is obtaired, from which the soundings for the smooth sheet shall be scaled. 

 For the immediate use of the hydrographer during his survey at least as many soundings 

 must be plotted on the boat sheet as are required to determine the adequacy of the 

 survey and the areas which need additional development. These soundings may be 

 recorded in a temporary Sounding Record or taken from the fathogram, at the discre- 

 tion of the hydrographer. 



3434. Soundings at Wharves and in Docks 



Where there are wharves and docks within the area of a hydrographic survey, 

 accurate sounding lines shall be run close to and along the outer faces of the wharves and 



