72 



HYDROGRAPHIC MANUAL 



values from the standard. If the error of a 

 leadline is more than 0.5 foot, it should be 

 remarked. 



3-68 Sounding leads. — Sounding leads in 

 standard weights of 5, 7, 9, 14, 25, 50, and 

 80 pounds can be requisitioned from Naval 

 Supply Depots, and other weights can be 

 purchased from commercial sources. Sound- 

 ing leads weighing 25 pounds or more are 

 for use with wire sounding machines. The 

 small leads, less than 25 pounds, should have 

 a cup-shaped depression in the bottom to 

 receive tallow, soap, or other arming mate- 

 rial to obtain bottom samples. Each survey 

 unit should have one lead with a snapper- 

 type sampling device attached (see 3-128). 

 Various methods may be used to attach the 

 lead to the leadline. The preferable method 

 is to make the leadline with a galvanized 

 thimble at the lower end to which the lead 

 is attached by a shackle. The sounding lead 

 and the snapper sampling lead can be inter- 

 changed on the same line; however, the lat- 

 ter should not be used for sounding. 



3-69 Sounding with a leadline. — As 



stated in 3-65, the leadline is used primarily 

 to supplement echo sounding on modem sur- 

 vey launches. If a leadline or sounding pole 

 is to be used extensively for sounding in 

 shoal water, a sounding chair should be 

 mounted on the starboard side of the launch. 

 When leadline soundings are taken, the lead 

 must be heaved ahead far enough to allow 

 it to sink to the bottom so that the leadsman 

 can feel the bottom and observe the sounding 

 when the leadline is taut and vertical. The 

 speed of the launch shall be reduced, if neces- 

 sary, to obtain vertical soundings. 



It requires some practice for a leadsman 

 to become proficient with the leadline and 

 to learn to read it correctly. At least one 

 man in a launch party should be trained in 

 the use of the leadline. 



3-70 Sounding machines. — A sounding 

 machine is a mechanical device, operated ei- 

 ther manually or by power, used to measure, 

 with wire, depths of water too great for the 

 handlead. Like the leadline, the sounding 

 machine is seldom used for hydrography. It 



is used principally to obtain bottom speci- 

 mens, to make vertical cast comparisons 

 with echo soundings, or to make oceano- 

 graphic observations. 



There are two types of sounding machines 

 in use by the Coast and Geodetic Survey. A 

 small, portable machine which is hand-op- 

 erated and used on launches ; and an LL-type 

 electric sounding machine used on ships and 

 auxiliary vessels where a power-driven ma- 

 chine is needed. A third type of machine 

 capable of sounding to 6,000 fathoms with 

 piano wire is no longer used. On new survey 

 vessels, the power sounding machines will be 

 replaced by oceanographic winches which 

 can be used for the occasional deep sound- 

 ings required. 



3-71 Hand sounding machine. — The hand 

 sounding machine (Fig. 21) has a bronze 

 reel which will hold more than 150 fathoms 

 of stranded sounding wire. The brake is a 

 wood-lined clamp operated by a small han- 

 dle above the reel. The hand cranks are 

 hinged so that they can be disengaged from 

 the shaft while the wire runs out, and en- 

 gaged for reeling in. The machine is usually 

 mounted at the stern of the launch and the 

 wire leads to a registering sheave overhang- 

 ing the stern far enough to keep the wire 

 clear of the propeller. The machine is used 

 to obtain bottom samples in depths too great 

 for the handlead, to obtain serial tempera- 

 ture and salinity observations on small craft, 

 and is frequently adapted for use with the 

 Price Current Meter. 



3-72 Electric sounding machine. — The 



LL-type sounding machine (Fig. 22) has a 

 reel with a mean circumference of V2 fathom 

 and will hold 900 fathoms of stranded wire. 

 It is driven by electric power, has a clutch 

 and brake arrangement which permits free 

 fall of the sounding lead, and a variable 

 speed for reeling in the wire. It is usually 

 mounted on or near the bridge. The wire 

 leads over a registering sheave suspended 

 above the machine to a fair-lead attached to 

 a pipe cross which turns freely on a pipe 

 boom rigged over the side of the ship. It is 

 used most frequently for obtaining bottom 



