CHAP. VIII. 1 



SOUNDING 



203 



be run first, and when the boat gets to the end of her allotted 

 space, she will return in the opposite direction, and run 

 intermediate lines. 



See Fig. 56, where we suppose the boat to start at A, work 

 along the long lines to B, and then return to C along the 

 intermediate lines, crossing the old work at every line, and 

 thereby getting a check on it. 



A lead-line of 7-stranded sounding-wire or cod-line, with Sounding 

 7 pounds lead, will enable soundings in shoal water to be 9^ '^^^^ 

 obtained at intervals of a few feet merely by lifting the lead Scales, 

 off the bottom and letting it go again for a fresh cast without 

 hauling it up and heaving it in the ordinary manner. The 

 boat must be kept accurately on pre-arranged transit lines, 

 and move very slowly. A skiff is most convenient for this 

 sort of work, and the leadsman should be close to the observer. 



Fig. 56. 



In sounding a harbour channel on a large scale, it is often sounding 

 convenient to stretch a lead-line across from side to side, and Sections, 

 sound at regular distances apart by this line, shifting it for 

 each section required. 



Sweeping for a reported pinnacle rock is resorted to when sleeping, 

 sounding fails to discover it. Two or more boats, pulling 

 abreast, tow a lead-line between them, well weighted under 

 the stern of each boat. If one weight in the centre is used, 

 the rock may very likely be missed. The size of the boats 

 will govern the length of line between them. An iron bar 

 is still better. It is by no means an easy thing to do efficiently, 

 so that all the ground shall be traversed without unnecessarily 

 going over it again and again. If steam-cutters are used, care 

 must be taken not to go too fast for the weights attached, or the 

 bight of line will be towed nearer the surface than is intended. 



