Page 257 hydrography 3423 



at ail angle when the lead strikes bottom, the ship should be maneuvered to bring the 

 wire vertical and the lead should be raised off the bottom to permit the wire to straighten 

 out, being subsequently dropped again in order to measure the depth. 



When taking vertical wire soundings the vessel must be stopped for each sound- 

 ing and, in addition to the time of each sounding, the time interval run between soundings 

 must be entered in the Sounding Record. The time at which the vessel starts ahead 

 and the time at which it stops are recorded, but these times are not necessarily the times 

 of the orders "to go ahead" and "to stop." The interval between them should ecjual 

 the time which would have been required for the vessel to traverse the distance if it 

 had been traveling at regular speed throughout the interval. The recorded time of 

 going ahead should be the instant just before the vessel has attained a normal speed 

 on course. The recorded time of stopping should be about midway between the time 

 of the order to stop and the time the vessel is stationary in the water. 



Errors in wire soundings occur from the lead not being vertically under the ship 

 and the wire not being straight. As stated above, the ship should be maneuvered 

 until the wire is apparently vertical before reading the depth. However, too much 

 reliance cannot be placed on the accurac}^ of such soundings, for the verticality of the 

 wire below the surface is unknown and in some cases uncertain. 



3423. Echo Sounding 



In contrast with handlead and wire sounding, echo sounding is an indirect method 

 of measuring the depths of the water. The soundings may be obtained while the 

 vessel proceeds at full speed and, for the depths of which the apparatus is capable, 

 the operation becomes principally one of navigation and position fixing. This method 

 of obtaining soundings and the various instruments and their use are described in 

 chapter 5. 



343. Frequency of Soundings (Sounding Interval) 



The interval between successive soundings along a line is determined by the 

 officer-in-charge, and depends on the depth of the water, the nature of the bottom, and 

 the method used to obtain the soundings. In general, sounding intervals should be 

 uniform between consecutive positions, but a uniform interval should not be rigidly 

 adhered to when soundings taken at irregular intervals will better define the bottom 

 profile. For convenience in plotting, a sounding should be taken at each position 

 and at regular intervals of time and distance between consecutive positions. 



3431. Frequency of Leadline Soundings 



In an area of even bottom and regular slope, an interval between handlead sound- 

 ings should be selected which will give the leadsman adequate time to obtain vertical 

 soundings without undue haste in his operations. The distance between handlead 

 soundings should never be so great as not to provide enough soundings according to 

 7724. This distance interval may be altered by adjusting either the time interval 

 between soundings or the speed of the vessel. Under normal conditions and at an 

 appropriate sounding speed, the following time intervals will usually be found satis- 

 factory for handlead soundings: 



Depths under 2 fathoms 1 5-second interval 



Depths from 2 to 4 fathoms 20-second interval 



Depths from 4 to 7 fathoms 30-second interval 



Depths from 7 to 10 fathoms 40-second interval 



Depths from 10 to 15 fathoms 1-minute interval 



