Page 213 hydrography 3312 



being AA, BA, CA, DA, etc., the second series being AB, BB, CB, etc., and likewise 

 for successive series. Primed letters, as A' , B' , etc., shall not be used. 



The colors to be used to identify the numbers and day letters of the positions are 

 blue, purple, green, and red, in that order of preference. Neither black nor yellow 

 shall be used for this purpose. 



A dead-reckoning line, controlled by astronomic sights, run in one general direc- 

 tion and of not more than a few days' duration, shall be considered as an entity and a 

 single letter shall be used to identify all the positions on it regardless of calendar days. 



Wlien hydrography is continuous, on a 24-hour basis, as in R.A.R., day letters 

 shall be changed at midnight, the first position after midnight being assigned a new 

 day letter. 



3312. Position Numbers 



The positions of a hydrographic survey shall be numbered consecutively for each 

 day's work. For this pm-pose positions shall be understood to include, in addition to 

 fixed positions, all positions at which control data of any kind are recorded, including 

 log readings, astronomic sights, bearings, etc., and time data required in the plotting. 



Numbered positions shall be recorded under all of the following circumstances, 

 whether or not accompanied by control data, when this is practicable: 



(a) At the beginning and end of each line. 



(6) When the sounding vessel has attained sounding speed at the beginning of a line or is slowed 

 down near the end of a line and at all other times when the speed is changed appreciably. 



(c) At all changes in course larger than 10°. When the vessel is small and the change in course 

 is immediately effective, the position may be taken at the middle of the change. Otherwise, a position 

 should be taken just before the course is altered and just as soon as the vessel is on the new course. 

 When soundings are not recorded around turns between the ends and beginnings of adjacent lines, 

 positions are not required between the last and first sounding of each line. 



In hydrography controlled by R.A.R., or any other means where fixed positions in quick succession 

 are not practicable, a fixed position should be obtained in the vicinity of each turn where it will best 

 control the sounding lines, other positions based on clock times or other data being recorded, by which 

 to plot the ship's course accurately (see 6812). 



(d) At all abrupt and considerable changes in depth. 



(e) At each detached sounding, including the least depth on a shoal which is being investigated. 

 Where drift soundings are taken over a shoal for the purpose of determining the least depth thereon, 

 several positions at which the shoaler depths are found shall be recorded in the Record. Xo record 

 need be made of other soundings obtained during the investigation except that a note must be made 

 in the Sounding Record stating the length of time spent in the investigation. (See 3666.) 



(/) At each sounding taken by any means with the vessel stopped, except as noted in 3313 for 

 vertical wire soundings taken close together. 



ig) Each time a position is fixed for any purpose whatsoever in connection with the survey, 

 whether or not to fix the position of a sounding. 



(h) At any incident to which it may be necessary to refer. 



In recording surveys run on preestablished ranges, as in 334, it may be desirable to 

 identify each position by the range it is on, rather than use the customary consecutive 

 numbering system throughout the day. The day letters should be used as usual, but 

 positions may be identified as range la-1, range la-2, etc., in which the letter is the day 

 letter, the first number is the number of the range, and the second number is the number 

 of the consecutive position on that range. In the records and on the sheets the control 

 stations should be marked to correspond with the identification used in the Sounding 

 Record. 



Where positions of the soundings are determined by linear measurements along a 

 range, each consecutive sounding may be identified by its distance from the front range 



