9332 HYDROGRAPHIC MANUAL PaGE 850 



In general the verifier will not need to consult records such as dead-reckoning 

 abstracts, astronomic data, and Bomb Records; or special reports on velocity of sound, 

 Radio Acoustic Ranging, or taut-wire sun-azimuth traverses. 



9332. Protracting 



The metal protractor should be checked before beginning work and at intervals of 

 a month or so thereafter (see 4533) . 



In checking protracting, consideration phould be given to the quality of work on 

 sheets previously verified, which were plotted by the same person or under the direction 

 of the same officer-in-charge. Where these have been found to be uniformly accurate 

 and carefully done, the amount of checking should be held to a minimum. With 

 no guide to the probable accuracy, the verifier should begin by verifying approximately 

 10 percent of the positions and, after convincing himself that the general accuracy of 

 the plotting is satisfactory, thereafter he should verify the protracting in the following 

 cases only: 



(a) Where positions? differ appreciably from tiie boat sheet (see 7671). 



(6) Where the depths at crossings or along closely adjacent parallel lines differ (see 7771). 



(c) Where there is reason to suspect, when inking the soundings, that a position has been 

 erroneously plotted (see 774). 



(d) All detached positions serving to locate critical soundings, rocks, or buoys (see 766). 



(e) Positions that cannot be reconciled with the time interval or course in the Sounding Record. 

 if) Adjacent positions, where other checks fail to reveal the cause of an excessive diflFerence in 



depths at a crossing of sounding lines. 



In all cases the boat sheet should be compared with the smooth sheet. If the 

 survey is not so complicated as to make it impracticable, a tracing of the sounding lines 

 on the smooth sheet may be made and superimposed on the boat sheet to reveal any 

 differences in protracting of the two sheets that should be verified. 



Errors in plotted positions may be due to careless protracting or mistakes made by 

 the person who plotted the smooth sheet, or they may be due to errors in the recorded 

 data in the Sounding Record. 



A metal protractor out of adjustment will result in errors in positions. This type 

 of error can be detected by the approximate uniformity of the errors. 



The three-point fix may be weak or almost indeterminate, as where the position 

 lies on or near the circumference of the circle passing through the three stations (a 

 revolver) (see 3332). 



Many of the errors which may occur in the recorded data are discussed in 3414, 

 3416. 7624A, and 774. 



9333. Soundings and Bottom Characteristics 



The penciled soundings are to be considered as a guide only. Every sounding on 

 the sheet shall be checked against the Sounding Record or the fathogram either at the 

 time it is inked or afterwards. The cartographer must also pay particular heed to the 

 spacing as indicated by the intervals between the recorded times of the soundings. 

 The standard spacing dividers should always be used for this purpose. In spacing 

 soundings the instructions in 7721 shall be followed. 



Special attention should be given to the placing of soundings around turns (see 

 3454 and 7682), to variations in the speed of the vessel (see 3351, 3461, and 7721), and 

 to variations in course between fixed positions (see 3352, 3463, and 7672). 



