7726 HYDROGEAPHIC MANUAL PaGE 722 



7726. Selection of Soundings From Fathograni 



Where the depths are recorded on a fathogram a different problem is presented. In 

 this case, soundings are selected from a continuous profile of the bottom along the line 

 traversed by the sounding vessel. The smooth plotter must have an appropriate spac- 

 ing in mind at all times, but he must not select the soundings by any regular spacing. 

 The soundings selected should, insofar as their frequency permits, present a numerical 

 record that will approximate the graphic profile. In all cases the least depth of a rise in 

 the bottom must be selected, and this must be followed and preceded by the greatest 

 depths, where practicable, irrespective of any intermediate soundings. Likewise, the 

 greatest depth of a depression in the bottom must be selected. In very irregular bottom 

 the number of these to be shown will be regulated, of course, by the number of soundings 

 that can be legibly shown on the smooth sheet in a given space. Intermediate sound- 

 ings shall be selected which will best delineate the actual profile. 



773. Penciling the Soundings 



In penciling the soundings, the smooth plotter must use every effort to achieve 

 clarity. Critical soundings shoidd never be obscured by placing soundings of lesser 

 importance too" close to them. A pencil hard enough to prevent smudging should be 

 used, but it must not be so hard as to indent or cut the surface of the paper. Generally, 

 a 3H pencil will be found satisfactory, but this will depend on the humidity of the 

 atmosphere at the time (see 724). 



As each day's soundings are penciled the plotter shall enter his initials with a colored 

 pencil in the appropriate space in Stamp No. 38, Processing, placed in the Sounding 

 Record at the end of each day's work (see fig. 183). 



7731 . Style of Numerals 



The penciled soundings shall be bold vertical numerals, drawn with single strokes. 

 Hair line or fancy lettering must not be used. The beginner will usually experience 

 some difficulty in penciling soundings neatly with even-sized numerals, but skill is 

 easily acquired with a little practice. 



7732. Size of Numerals 



Most of the numerals representing soundings should be about 2 mm in height. The 

 size of the numerals, of course, should vary somewhat according to whether the sound- 

 ings are sparse or congested in any given area. In areas where the soundings are 

 sparse the size should be increased about 10 percent, and in congested areas should be 

 reduced about 10 percent. Ordinarily, no sounding numeral should be less than 1.8 

 mm in height, although even this limit may have to be lowered for areas in which the 

 soundings would otherwise be illegible. The important things to remember are, first, 

 that no sounding should ever be illegible and, second, that in order to present a pleasing 

 appearance a uniform size of numeral should be maintained as far as practicable. 

 (See fig. 163.) 



In areas of intensive development where individual lines of soundings are difficult 

 to follow, the numeral representing the least depth should be drawn slightly larger and 

 bolder. Such depths are the most important soundings in the area, and a cursory 

 examination of the sheet should disclose these without the need for a meticulous sound- 

 ing-by-sounding examination of the areas. (See also 7753.) 



