74 



HYDROGRAPHIC MANUAL 



oceanographic winches and there is not suf- 

 ficient deck space to mount an LL-type 

 sounding machine, vertical cast soundings 

 may be obtained with an oceanographic 

 winch. In most instances a %2-inch flexible 

 steel cable will be used on the winch. A 

 bathythermograph winch with % 2 -inch flex- 

 ible aircraft cord may be used to a depth of 

 about 400 fathoms. A registering sheave 

 must be used in either case and the sheave 

 must be calibrated for the size cable being 

 used. If the sheave measures depth in meters, 

 the sheave reading should be recorded in 

 meters and the equivalent depth in fathoms 

 entered below it. 



3-75 Stranded sounding wire. — Stranded 

 sounding wire is composed of seven tightly 

 twisted strands of double-galvanized No. 24 

 B.W.G. gage wire, and has a breaking 

 strength of not less than 500 pounds. It is 

 furnished in 300-fathom lengths, packed with 

 powdered lime in sealed cans. The diameter 

 of the stranded sounding wire is 0.065 inch. 



When it is necessary to splice stranded 

 wire, a regular long wire splice should be 

 made, with the wires ending at varying dis- 

 tances apart throughout the length of the 

 splice. The ends should be tucked and the 

 splice seized with fine copper wire at both 

 ends and one or two places in the middle. 

 The whole should be cleaned with muriatic 

 (hydrochloric) acid and washed with a thin 

 coating of solder. 



The reel of the sounding machine should 

 be dry and freely coated with mineral grease 

 before the wire is wound on it. New wire 

 should be coated with oil as it is put on the 

 reel. When in use, and especially after the 

 last sounding of the day, the wire should be 

 run through a piece of well-greased canvas 

 as it is reeled in. A brush dipped in heavy 

 oil should, be held occasionally against the 

 wire on the reel while reeling in, and the 

 reel of wire should be well wrapped with oil- 

 soaked cloths. The sounding machine should 

 be protected by a canvas cover when not in 

 use. 



3-76 Echo sounders. — Nearly all sound- 

 ings are obtained by echo sounders which 



record a continuous profile of the bottom 

 under the survey vessel. Various instru- 

 ments have been used in the past. Three types 

 of recording sounders now in use for survey 

 purposes are described in the following para- 

 graphs and no others shall be used unless 

 specifically authorized by the Director. 



All echo sounders operate on the basic 

 principle that a sound produced near the 

 surface of the water will travel to the bottom 

 and will be reflected to the surface as an 

 echo. The echo-sounding equipment is de- 

 signed to produce the sound, receive and 

 amplify the echo, measure the intervening 

 time interval, convert the interval into units 

 of depth measurement, and record the depths 

 on a moving graph. The sound is an electric 

 pulse which is mechanically converted to 

 sound by a transducer in the hull. Trans- 

 ducers with various frequencies are used for 

 different ranges of depth and for specific 

 purposes. A low frequency is used for sound- 

 ing in deep water, since high frequency 

 signals are subject to greater absorption and 

 require greater initial power for successful 

 use in deep water (see 3-96 to 102). 



Sound travels in water at a fairly constant 

 velocity ; however, this velocity changes with 

 temperature, salinity, and depth (pressure). 

 Echo-sounding instruments are operated for 

 a certain assumed velocity of sound, known 

 as the calibration velocity, and any sound- 

 ing is in error by an amount directly pro- 

 portional to the variation of the actual from 

 the assumed velocity. 



Velocity corrections shall be determined on 

 all hydrographic survey projects, but correc- 

 tions may be disregarded when they are less 

 than half of one percent of the depth. 



3-77 EDO 185 (AN/UQN).— An echo 

 sounder known as EDO 185, or AN/UQN 

 (Fig. 24), is standard equipment for hydro- 

 graphic surveys in depths greater than 100 

 fathoms. The transmitter, oscillator, receiver, 

 power supply sections, recorder, indicator, 

 and control panel are contained in a cast 

 aluminum alloy cabinet designed for bulk- 

 head mounting. The EDO 185 is not a port- 

 able sounder, although it is possible to mount 

 it in a launch for special surveys. 



