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surveyed is not distant from the control, two officers, one recorder, one fathometer 

 attendant, and one helmsman will ordinarily suffice for visually controlled hydrography; 

 but where the signals are distant, or difficult to observe because of haze or other reasons, 

 it is frequently necessary to have two anglemen to take the sextant observations, 

 leaving the officer-in-charge free for plotting. 



For hydrography controlled exclusively by the R.A.R. method, the officer-in- 

 charge is sufficient on the bridge under ideal conditions, but when this method of con- 

 trol is combined with visual control, as it frequently is, additional officers are required. 

 A chronograph attendant, a radio technician, and a bomber are additional personnel 

 needed for the various operations in R.A.R. control; their duties are described in 671. 

 When R.A.R. controlled hydrography is continued at night or in reduced visibility, 

 additional officers are required on the bridge; one of these directs his attention exclu- 

 sively to the navigation and safety of the vessel. 



Ship operations, such as taut-wire traverse, sun-azimuth observations, and 

 bombed distances for the determination of the horizontal velocity of sound, require 

 personnel who are exceptionally alert and efficient, because a failure to make or record 

 any one of the observations may require the repetition of the entire operation. The 

 number of personnel required for the various operations depends somewhat on the 

 location of the apparatus, and under ideal conditions some of the duties may be combined 

 and performed by one person. For example, in simultaneous operations the observers 

 reading and checking the taut-wire sheave may also be able to take the inclined and ver- 

 tical angles, which are always observed between sheave readings. If the chronometer 

 is conveniently located, the recorder may be able to mark the times directly on it, or in 

 other instances may use a watch which has been previously compared with the chro- 

 nometer. The fathometer attendant is, of course, needed only when a sounding line is 

 run simultaneously with the other operations. The fathometer attendant can fre- 

 quently serve also as pelorus attendant. On shipboard the several men on watch are 

 used as required, the quartermaster on watch serving to carry messages where needed, 

 and other members of the crew being available as hand leadsmen, or to operate the 

 sounding machine if required. 



A topographic, signal-building, or triangulation party unit usually consists of one 

 officer and three men. If these parties are transported ashore from the ship, additional 

 personnel are required for the launch crew. If they are based in camp, a cook and camp 

 attendant must be provided. 



The efficiency of the survey party and the quality and quantity of the results 

 obtained will depend largely on the experience and qualifications of the officers and 

 men and the interest and pride they take in their work. Assignments should be based 

 on the experience and general aptitude of each individual, and the degree of reliability 

 that can be placed in his work. One of the functions of the officer-in-charge is to 

 encourage the personnel to learn their duties and become proficient in their work, and to 

 provide them with opportunity for obtaining the necessary all-round experience to 

 enable them to assume charge of similar operations when called upon to do so. 



143. Tide Stations 



Tidal data are required for determination of the various datum planes, for the 

 prediction of tides, and for use in a hydrographic survey. 



Tide stations shall be established in the immediate vicinity of the hydrographic 

 operations in order that the soundings may be accurately reduced to the sounding 



