8312 HYDROGRAPHIC MANUAL PaGE 778 



Record, preferably at the end of each day's record, the initials of the persons entering 

 and checking the velocities should be recorded. 



Distances in meters are no longer used in plotting R.A.R. smooth sheets (see 763), 

 and need not be determined. All R.A.R. smooth sheets are plotted at an assumed 

 velocity of sound of 1,460 meters per second. Therefore the elapsed times must be 

 converted to account for the difference between the actual velocity of sound and a 

 velocity of 1,460 meters per second. It is necessary to change the actual elapsed times 

 to what they would have been had the velocity been 1,460 meters per second. There 

 are several methods of making this conversion. The increment to be added to the 

 elapsed time (because the actual velocity will almost always be greater than 1,460 

 meters per second) may be found from the following relation: 



T- , actual velocity— 1,460. , , , ,. 



increment = , .^^"^ X elapsed time 



These increments may be determined with sufficient accuracy on a slide rule. 

 Table 36 contains factors by which the elapsed times may be converted into times at 

 the plotting velocity; a computing machine should be used. These factors may also 

 be used to construct a graph or a table of increments for a limited range of velocity. 

 The converted times to be used in plotting the smooth sheet should be entered in the 

 Bomb Record in the spaces to the right of the corresponding elapsed times. 



The Bomb Records shall constitute a part of the permanent records of an R.A.R. 

 survey. The volumes shall be numbered separately and consecutively in the proper 

 chronological order. The cover label and title page of each volume shall be completed 

 in accordance with the instructions in 8196 for the Sounding Record. The registry 

 number of the survey shall be entered in pencil in the proper space. The total number 

 of bomb positions should be given, followed in parentheses b}^ the number used to control 

 the hydrography. 



8312. R.A.R. and Dead Reckoning Abstract 



The use of the R.A.R. and Dead Reckoning Abstract (Form 722) is not required for 

 surveys controlled wholly by R.A.R. It is a convenient work sheet, however, which 

 many hydrographers prefer to use for ready reference while plotting the positions on the 

 boat sheet. Some of the entries duplicate the information contained in the Sounding 

 Record. However, it contains the only record of the elapsed times from R.A.R. sta- 

 tions available at the plotting station. The velocity used in plotting each distance on 

 the boat sheet should be entered in the "Remarks" column, or if the same velocity is used 

 in plotting all distances it should be entered at the top of each page. 



For surveys controlled wholly by R.A.R., the abstract shaU not constitute a part 

 of the permanent records. They should be made available for use by the smooth-sheet 

 plotter, but may be destroyed after the smooth sheet has been verified and reviewed 

 at the Washington Office. They should not be transmitted to the Office. 



Occasionally, dead reckoning must be used to supplement R.A.R., as for example on 

 offshore loops (3371); in such cases Form 722 must be used, and should accompany 

 the other records of the survey, and be forwarded to the Washington Office. After the 

 survey has been reviewed, the abstracts are destroyed. 



Form 722 must always be used in connection with astronomic control and should 

 be forwarded with the other records of the survey when they are transmitted to the 

 Washington Office. 



