1. GENERAL REQUIREMENTS 



13 



frequency to obviate the necessity of apply- 

 ing- velocity corrections (see 5-120) . The fre- 

 quency meter reading shall be recorded at 

 least once each hour. Bar checks shall be 

 recorded twice daily when circumstances 

 permit. 



On large vessels where bar checks are not 

 practicable, vertical cast comparisons shall 

 be made and recorded at selected intervals 

 when good casts can be obtained. 



1-37 Fathograms.— Stamp No 31 shall 

 be impressed at the beginning and end of 

 each fathogram and all required information 

 recorded to identify the record with the sur- 

 vey. Position fix marks shall be numbered 

 consecutively and the day letter shown at 

 every tenth position. Positions where the line 

 begins, breaks, or turns about should be 

 indicated (see 5-31). The phase or scale 

 being used shall be indicated at each change. 

 The PDR phase changes are automatic with 

 base scales in multiples of 400 fathoms. The 

 base must be indicated on the fathogram 

 as plus, 400 plus, 800 plus, etc. 



Fathograms may be folded in accordion 

 style or filed in rolls. The first method is 

 preferred (see 5-32). 



1-38 Depth units.— The depth unit of 

 hydrographic surveys in the Atlantic Ocean, 

 Gulf of Mexico and bodies of water tributary 

 thereto shall be integral feet except for 

 those offshore surveys which are entirely be- 

 yond the limits of charts whose depth unit 

 is feet, in which case the depth unit of the 

 survey shall be fathoms. In certain areas, 

 such as the coast of New England, where 

 echo sounders are operated on the fathom 

 scale for most of the survey, the boat sheets 

 may be plotted in fathoms, but the smooth 

 sheet shall be plotted in feet unless other- 

 wise directed by project instructions. 



The depth unit of hydrographic surveys 

 in the Pacific Ocean and bodies of water trib- 

 utary thereto shall be fathoms, except that 

 where the major part of the survey is within 

 the limits of a chart whose depths are in 

 feet, the smooth sheet shall be plotted in feet. 



Although the depths in the sounding rec- 

 ord may change from one unit to another 



within the area of the survey or within the 

 same sounding records, they are all reduced 

 to the unit to be used on the smooth sheet. 

 Only one unit, fathoms or feet, shall be used 

 on any boat or smooth sheet. 



Soundings shall be recorded in integers, 

 or to the nearest decimal part, according to 

 Table 2 and the following rules : 



(a) Echo soundings with the 808 Fathom- 

 eter or EDO 255 for a hydrographic survey 

 to be plotted in feet shall be recorded in 

 FEET and DECIMALS except for (b) and 

 (c); 



(b) Where 808 type graphic-recording 

 instruments, which can be operated to record 

 in either feet or fathoms, are used in areas 

 of irregular bottom, the first phase in feet 

 shall be used to its limit, but, where numerous 

 changes in phase would be required on the 

 foot scale, fathoms shall be used for greater 

 depths ; 



(c) Where EDO 255 graphic-recording 

 instruments, which cannot be changed from 

 one mode to another at will, are used, the 

 recorder shall be operated on the foot scale 

 to the maximum practicable extent in areas 

 charted in feet. In areas where depths ex- 

 ceed the limit of the foot scale or the sub- 

 marine features are very irregular, the in- 

 strument shall be operated on the fathom 

 scale. 



(d) All depths measured by echo-sounders 

 for a hydrographic survey to be plotted in 

 fathoms shall be recorded in fathoms and 

 decimals except for (e) ; 



(e) Where practicable, the shoal water 

 soundings obtained by echo-sounders for a 

 survey to be plotted in fathoms shall be ob- 

 tained on the first phase in feet. 



(f) Wire soundings shall be recorded in 

 fathoms and decimals. 



(g) Hand lead soundings interspersed 

 with echo soundings shall be recorded in the 

 same unit as the echo soundings. 



(h) Hand lead soundings in depths less 

 than 11 fathoms and pole soundings shall be 

 recorded in feet and decimals. 



1-39 Reduction of soundings. — Recorded 

 soundings must be corrected for any depart- 



