Page 721 the smooth sheet 7725 



Where the appearance of the smooth sheet is the only criterion, the following rules 

 may be used for general guidance, always bearing in mind that legibility and clearness 

 are of prime consideration: 



(1) Where the horizontal axis of the numeral approximately parallels the direction of the sounding 

 Ime, 1-digit numerals should be spaced about 7 to an inch, 2-digit numerals about 5 to an inch, and 

 3-digit numerals about 4 to an inch. 



(2) Where the horizontal axis of the numeral is approximately normal to the direction of the sound- 

 ing line, the most satisfactory spacing is about 7 numerals to an inch. 



(3) Where numerous fractions, or decimals, are to be shown, these may be considered as equivalent 

 in width to about one-half digit. 



In congested areas at least 50 percent more soundings can be legibly shown in the 

 same space without undue confusion, if care is used (see 7732 and fig. 163). 



7725. Selection of Soundings 



Where all of the recorded soundings are not to be shown on the smooth sheet a care- 

 ful selection must be made so that those shown will most nearly represent the actual 

 bottom relief. In no case, except where the bottom is practically flat, shall a mere 

 mechanical selection be used, as for instance the selection of alternate soundings. The 

 sounding obtained on a fix should always be shown. Between fixes, where a selection 

 is necessary, the general rule is that both the deepest and shoalest soundings must be 

 shown, interspersed with as many other soundings as can be conveniently shown. It is 

 absolutely essential that the final result show the least depth on shoals, the greatest and 

 least depth in channels, all changes of slope, and those soundings which are essential to 

 the correct delineation of the depth curves. 



In penciling soundings on the smooth sheet, it is essential that dangers and im- 

 portant depths be not obscured by numerous soundings of lesser importance. As the 

 progress of penciling rev^eals the important features it will frequently be found neces- 

 sary to delete some of the plotted soundings to permit showing those of more import- 

 ance. To assist in drawing attention to important features, such as rocks awash, 

 sunken rocks, and least depths on shoals, frequent use shall be made of leaders pointing 

 to these (see 7753) . 



The low-water line is one of the most important depth curves on the smooth 

 sheet, and it is essential that it be located as accurately as possible. All of the soundings 

 that will aid in defining its location shall be shown in pencil on the smooth sheet. 

 (See 754.) 



At crossings of sounding lines and occasionally where two parallel sounding lines 

 approach one another closely, the soundings of one line wiU conflict in position with 

 those of another hne. In selecting the soundings in such cases, the same considerations 

 must govern as in the case where aU the soundings on one line cannot be shown. In 

 general, the least depth should be selected. 



Wliere soundings have been taken over even mud or sand bottom and there is a 

 plethora of soundings of approximately the same depth, it is unnecessary to show them 

 with the frequency used for uneven bottom. In such cases they should be plotted 

 with only about two-thirds the frequency stated in 7724. 



Recorded soundings that are not used in the smooth-sheet plotting should be 

 marked "N.P." in the Sounding Record, the notation being entered in color (see 7624) 

 after the final reduced sounding. 



465382—44 47 



