Page 719 the smooth sheet 7721 



from the recorded times shall be made for the pm-pose of improving crossings, or for 

 other reasons, unless other data prove that the recorded times are in error. Such 

 errors usually occur only in the hours or minutes, and if the interval between positions 

 is relatively short, as it usually is in three-point fix hydrography, an error in the min- 

 utes is easily detected. 



Where the depths between positions are uniform, a slight displacement in the 

 positions of the soundings is immaterial, and no appreciable time should be expended 

 in obtaining precise spacing. In irregular depths, however, the spacing as recorded 

 must be closely followed. 



AU soundings must be plotted on the pencil lines connecting consecutive positions 

 (see 7682). 



Where soundings fall close to control stations in the water area, care must be taken 

 that the soundings do not obscure the actual station points. In general, in unim- 

 portant areas of uniform bottom, soundings should not be shown inside a station 

 symbol. But there should be no hesitancy to break the station symbol to show an 

 important sounding. 



7721. Spacing Three-Point Fix Hydrography 



In tlu^ee-point fix hydrogi-aphy positions are usually taken at regular intervals 

 and at even minutes of time (see 3313). This simplifies the plotting of the soundings 

 between positions. If the soundings are taken at uniform intervals, as is generally the 

 case in handlead work, the spacing dividers are used to subdivide the distance between 

 positions into the required number of spaces, and the soundings are plotted. If the 

 sounding interval is not uniform, the soundings must be plotted according to their 

 respective times. In such cases the spacing dividers are used as a time-measuring device. 

 (See 343 and 4813.) 



Wlien the speed of the vessel is changed materially between positions it must be 

 taken into account in spacing the soundings. This is particularly important in launch 

 and small-boat hydrography at the beginning of lines near the beach, where the launch 

 or boat starts from a standstill or slow speed, increasing to full speed soon there- 

 after. A similar allowance is often necessary near the end of a sounding line near 

 the beach where the speed may be reduced as the launch approaches the shore. 

 Occasionally, such changes are made far offshore; as for instance, when it is necessary 

 to slow down to avoid collision with a passing vessel. Because of momentum, of 

 course, the increased or decreased speed is effective only gradually after the time noted 

 in the Sounding Record. (See also 3461.) 



7722. Spacing R.A.R. Hydrography 



In R.A.R. hydrography, positions do not necessarily comcide with even mmutes 

 of time, and as the soundings are recorded according to time intervals there will not 

 always be a soimding on the position; neither can the soundings be spaced evenly 

 from position to position. In using the spacing dividers the points must be set accord- 

 ing to time, starting mth the minute immediately preceding or following any R.A.R. 

 position which does not occur at an even minute (see 4813). Otherwise, soundings 

 controlled by R.A.R. are spaced in a manner similar to that used in other methods of 

 control. 



a. Tabulation of crossings on R.A.R. sheets. — Because of the relative weakness of 

 R.A.R. control in certain areas a penciled tabulation of the depths at crossings shall 



