5. HYDROGRAPHY 



173 



(d) An index of all objects such as sig- 

 nals, landmarks, rocks, aids to navigation, 

 and breakers, the positions of which have 

 been determined by sextant angles shall be 

 entered as follows: The recorder shall make 

 an appropriate entry on page 2 of the vol- 

 ume in which the data are recorded, and 

 the entry shall be repeated in volume one 

 of the set of records. If the data concerns a 

 presurvey review item, reference to the item 

 number should be made. 



(e) All calibrations shall be indexed on 

 page 2 of the volume in which the data are 

 recorded, including bar checks, vertical cast 

 comparisons, phase comparisons, leadline 

 comparisons, and calibrations of Shoran, 

 EPI, or Raydist equipment. 



Correction of Soundings 



5-100 General requirement. — Recorded 

 sounds must be corrected for any departure 

 from true depth due to the method of sound- 

 ing or to a fault in the measuring apparatus 

 and for the height of the tide above or be- 

 low the plane of reference at the time of 

 sounding (see 1-39). Vertical columns are 

 provided in the sounding record for enter- 

 ing the various corrections and the corrected 

 soundings. 



Corrections (often called reducers) shall 

 be entered in the same unit in which the 

 soundings have been recorded, either fathoms 

 or feet, and parts of units shall be entered 

 as decimals. 



Each correction, with its arithmetical sign, 

 shall be entered on the horizontal line oppo- 

 site the first sounding to which it applies and 

 need not be repeated, except opposite the 

 first sounding on each page. A correction 

 once entered shall be considered applicable 

 to all following soundings until a different 

 correction or sign is entered. 



Specific rules for determination and appli- 

 cation of various types of corrections are 

 stated in the following sections. 



5-101 Correction units. — Corrections to 

 soundings shall be entered according to 

 Table 2. It should be noted that, in general, 

 the corrections are to be entered to a deci- 



mal which is one-half that required in re- 

 cording the soundings, using 0.2 where the 

 requirement for recording is 0.5. Exceptions 

 are: that no entry in fathoms need be closer 

 than 0.1 fathom ; and for soundings in feet, 

 except on shoals, banks, and other critical 

 areas, corrections need be entered only to the 

 nearest foot. Used in conjunction with Table 

 2, the following tabulations may be helpful: 



The range through which any correction 

 is to be applied is as follows : 



Where corrections are entered to the 

 nearest 0.5 foot or less, and to the nearest 

 0.1 fathom, the range covered shall be 

 from one-half below to one-half above the 

 correction applied, according to the fol- 

 lowing tabulation : 



Whether added to or subtracted from 



the sounding 



Ranae 



0.1 to 0.3 foot = 0.2 foot. 



0.3 to 0.5 foot = 0.4 foot. 



0.5 to 0.7 foot = 0.6 foot, 

 etc. 



0.25 to 0.75 foot = 0.5 foot. 



0.75 to 1.25 feet =1.0 foot 



1.25 to 1.75 feet - 1.5 feet 

 etc. 



0.05 to 0.15 fathom = 0.1 fathom. 



0.15 to 0.25 fathom = 0.2 fathom. 



0.25 to 0.35 fathom = 0.3 fathom, 

 etc. 



Where corrections are entered to the 

 nearest 1.0 foot or to the nearest 0.2 fathom 

 or greater, the range covered shall be 

 eccentric, from one-fourth below to three- 

 fourths above the correction applied, or 

 vice versa, according to the following 

 tabulations : 



