.\ <^ 



BUOY TO BE LOCATED 



Page 121 control and signal building 2532 



bearings to the two buoys will indicate that the ship is on the range. If the azimuth 

 between the buoys has been previously determined, the correct observation station 

 may be found more easily by bringing the proper buoy on this bearing. 



2532. Taut-Wire Distances From Two Stations 



The location of a buoy beyond the visibility of shore stations, or other buoys, is 

 more difficult, and the corresponding computation 

 or the graphic determination of the buoy position 

 becomes more involved. The preferable method, if 

 the ship is equipped with a taut-wire apparatus, is 



, . , . » , , . BUOY AT KNOWN POSITION 



to measure the taut-wire distances trom the buoy, \\y o 



...--, . ^ THREE POINT FIX \ COMPilTEO OISTINCE , ^^ 



whose position is to be determined, to two or more -,\ /& 



known positions in sufficiently divergent directions. 



Such a location has an additional value in R.A.R. "% 



surveys, since accurately measured distances, distri- 'q- 



buted throughout the area of the project, have a 



supplemental use in the determination of the experi- figure 25.-Buoy location by 



. /*nr't\\ taut-wire distances. 



mental velocity oi sound (see 6352). 



To measure the distance between two buoys by this method, the approxim^ate 

 azimuth between them must be known. The ship proceeds along this course, noting the 

 reading of the registering sheave of the taut-wire apparatus as each buoy is passed 

 abeam, and at the same time the direction and velocity of the current are noted. The 

 direction is observed by compass in the usual manner when the ship is directly down 

 current from the buoy and is recorded in the appropriate space on Form 777, Taut-Wire 

 Traverse Observations. Before determining the geographic position, the measured 

 distance must be corrected for the scope of the anchor cable by using the current 

 observed at each buoy. 



Taut-wire measurements may be made between strong three-point fixes, at the 

 approximate limit of visibility of shore stations, and the buoy to be located. The 

 angles determining the inshore positions should be observed from a point near the taut- 

 wire sheave, or else the sheave should be read when the buoy is abeam of the same 

 part of the ship from which the angles were observed. 



The position of a buoy from distances measured by taut wire is best determined 

 graphically. This is especially true when the method is employed in combination with 

 locations by subaqueous sound ranging, which are generally determined by graphic 

 methods (see 2533). The position may be determined by computations if desired. 

 Having two sides of the triangle measured by taut wire, the third side is either known 

 or may be determined by an inverse computation between the two known stations, 

 from which taut-wire distances were measured. A spherical triangle with three sides 

 known may be solved by the use of formulas found in Shortrede's Table of Logarithms. 



2533. Subaqueous Sound Ranging 



In R.A.R. surveys a buoy is often located by distances obtained by subaqueous 

 sound ranging. The method depends on the presence of accurately located stations, 

 designed for the reception of subaqueous sound, distributed so as to furnish good inter- 

 sections at the buoy to be located, and furthermore, at unequal distances so that the 

 returns from the stations will not be simultaneous n*or indistinguishable on the chrono- 

 graph tape records (see 6814). The accuracy of the method depends on the use 

 of the correct velocity of sound through the water, and this, in some localities, is 



465382—44 10 



