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HYDROGRAPHIC MANUAL 



Where a fraction stands alone the hori- 

 zontal bar between the numerator and de- 

 nominator must be included to avoid mistak- 

 ing the component parts as whole numbers. 

 The bar shall be omitted when the sounding 

 is a mixed number. 



The decimal part of a fathom shall be 

 plotted as the numerator of a fraction 

 whose denominator is 10, but with the de- 

 nominator omitted. The horizontal bar of 

 the fraction shall be retained. Where depths 

 are less than one fathom, the decimal part 

 shall always be preceded by a zero, as 0*. 

 Great care is necessary when penciling and 

 inking soundings that numbers in a fraction 

 or decimal cannot be mistaken as whole num- 

 bers and that they are not separated from 

 the integers in mixed numbers. 



6-58 Soundings at positions. — The center 

 of the number, including the fraction if any, 

 is considered the position of that sounding 

 except for soundings at positions. In pencil- 

 ing and inking soundings at positions it 

 is important not to obscure the position 

 dot, or position number, by any part of the 

 sounding. A single digit sounding should be 

 slightly displaced if necessary to avoid ob- 

 literating the position dot, however a single 

 digit representing the least depth on a sunken 

 rock or pinnacle should be centered on the 

 position. For 3-digit soundings the first digit 

 shall be placed to the left of the dot and the 

 others to the right of it. 



Digits adjacent to position dots shall 

 never be positioned so that the dot might 

 close any part of the digit thus changing 

 its value on photographic copy. If a 6 or 9 

 are so drawn that the dot is below or above 

 the tail, respectively, the figures might be 

 misread as 8. The same precaution should 

 be taken when drawing the figure 3. 



6-59 Spacing of soundings. — Soundings 

 are recorded at regular intervals appropriate 

 to the scale of the survey, speed of the 

 sounding vessel, and depth of the water (see 

 5-29). Additional soundings are scaled from 

 fathograms as necessary to reveal the bottom 

 configuration. 



The spacing or density of soundings on 



the smooth sheet shall be such that all depth 

 curves are adequately delineated and the 

 configuration of the bottom fully revealed. 

 These objectives are partially accomplished 

 by the spacing of sounding lines. The spacing 

 of soundings between positions shall be gen- 

 erally uniform on the smooth sheet, except 

 as noted in 6-60. This requirement should 

 be considered when there are noticeable dif- 

 ferences in distances between consecutive 

 positions, as when parallel lines are run with 

 and against strong currents. 



For generally smooth bottom the spacing 

 of soundings on east-west lines should not 

 exceed 5 mm for single-digit numbers, 7 mm 

 for 2 digits, 10 mm for 3 digits, and 15 

 mm for 4-digit numbers. On north-south 

 lines the spacing should be 5 mm for single- 

 digit numbers to 7 mm for 4 digits. The 

 spacing for mixed numbers, integers with 

 fractions or decimals, should be slightly less 

 on east-west lines. These are general cri- 

 teria useful where a selection of soundings 

 is possible (see 5-29). 



Where the bottom is irregular the spacing 

 of soundings will also be irregular because 

 of the requirement to plot soundings at 

 abrupt changes in the slope of the bottom 

 and the peak and deep soundings which 

 characterize the bottom as bumpy, undulat- 

 ing, ridged, or channeled. Soundings which 

 mark least depths on dangers to navigation 

 and deep soundings which reveal channels 

 for navigation are most important. In plot- 

 ting multiple-digit soundings in some areas 

 it may be necessary or advisable to decrease 

 the routine spacing between soundings and 

 to orient 3- and 4-digit soundings at an 

 angle (Fig. 84, also see 6-14). 



The primary consideration when plotting 

 soundings is that each sounding shall be 

 plotted in its correct geographic position as 

 established by the sounding interval or frac- 

 tion of an interval and the speed and course 

 of the sounding vessel. Accurate spacing of 

 soundings between fixed positions is attained 

 with the use of a spacing divider. When 

 using this guide, a continual surveillance of 

 the sounding record is required to note 

 changes of speed or course and changes in 



