8142 HYDROGRAPHIC MANUAL PaGE 762 



8142. Time 



Standard time shall be used in all hydrographic recording and the standard merid- 

 ian shall be noted at the head of the "Time" colmnn at the beginning of each day's 

 work (see 151). Time shall be recorded by numbering the hours consecutively from 

 (midnight) to 23 (11 p. m.). 



All times shall be recorded in the "Time" column, with the corresponding data 

 to which they refer entered on the same horizontal line. The exact time of each posi- 

 tion, each recorded sounding, and each entry that will be used in plotting, must be 

 recorded. Additional events which need to be timed in the Record are explained in 

 different parts of this Manual — among the most important are: the time of an R.A.R. 

 position (6811), the exact time of irregularly spaced soundings (3431 and 3433), the 

 tunes of stopping for vertical casts and going ahead (3422), the times of changes in 

 course (3373) and turns (3463), and the times of turns at ends of lines. 



In connection with vertical casts, the abbreviations st. for stop and ah. for ahead 

 shall be entered immediately preceding their respective times on the horizontal Ime, 

 immediately before and after the respective soundings. 



It is important that the exact times of the following detached events be recorded: 

 detached soundings which are not a part of a sounding line; least depths on a shoal 

 covered by drift sounding, or otherwise, with only the critical soundings recorded; 

 positions to determine the outline or limits of an area where a tidal plane of reference is 

 involved ; a measurement or estimate of the height of a shoal or rock above the water, 

 or an estimate of the depth of water over a feature on which a sounding cannot be taken. 



If two or more clocks are used for the times of different parts of the recorded data, 

 as in R.A.R. control, they must be set in agreement at the beginning of the day and 

 verified at intervals throughout the day (see 6811). 



8143. Soundings 



The soundings shall be entered in the double column headed "Soundings", leaving 

 one blank horizontal line after each position. Every sounding shall be recorded in 

 fathoms and decimals, or feet and decimals (see 124) ; no sounding shall be entered in 

 fathoms and feet; fractions shall not be used. The integers of the numbers shall be 

 recorded in the left-hand column, the tenths being recorded in the right-hand column. 

 The depth unit shall be indicated by drawing lines through the inapplicable subhead- 

 ings at the top of the double column on each page. 



The depth units in wliich the soundings are to be recorded in various circumstances 

 are specified in 3112. There is no objection to changing from one unit to another in 

 the recorded soundings; where this is done soundings shall be omitted from two hori- 

 zontal lines, in which the new unit is to be boldly indicated (see fig. 172). Since only 

 one depth unit is used on one hydrographic sheet (see 771 and 823) it is more convenient 

 that as large a percentage of the recorded soundings as practicable is in this unit, and 

 that changes from one unit to another are held to a minimum. 



Handlead soundings for comparisons, or interspersed with echo soundings, shall 

 be in the same unit as the echo soundings. 



No bottom soundings are almost valueless, but where they cannot be avoided they 

 are to be recorded thus, f^, meaning that at 18 (fathoms) bottom was not reached 

 (see 3542). 



Soundings shall be recorded in integers, or to the nearest decimal part, according 

 to table 29. 



