4663 HYDROGKAPHIC MANUAL PaGE 398 



bottom of the pipe lead, or an ordinary lead for that matter, for obtaining bottom 

 samples. 



4663. Lead for Very Soft Bottom 



A special lead can be made for use in ooze or very soft mud. An iron rod, K by 

 10 inches, with an eye in one end, is threaded throughout its length. A perforated 

 wooden disk, reinforced by steel bands, is attached just below the eye. Below the 

 disk, 2- to 4-pound sections of sounding lead drilled through the center are screwed on 

 the threaded rod. The whole is held in place by a nut above the disk and one below 

 the lead. Any desired weight of lead and size of disk may be used but a 7-inch disk 

 and 10 pounds of lead will usually be found satisfactory. The leadline should be 

 graduated from the top of the disk. 



4664. Arming the Lead 



The sounding lead is armed to bring up for inspection specimens of the bottom. 

 The depression, or grooved-out hole, in the bottom of the lead is filled with soap, 

 tallow, or a mixture of both. Sand, mud, shells, and pebbles will adhere to these 

 matei'ials and be brought to the surface for inspection so that a description of them 

 may be recorded in the Sounding Records. Some types of mud will not adhere to 

 tallow or soap, in which case the snapper should be used. The sample of deposit 

 brought up is but superficial, and is no criterion of what lies beneath. (See also 384 

 and 476.) 



4665. Detaching Rod and Sinkers 



The Belknap-Sigsbee specimen cylinder, commonly known as a detaching rod, is 

 a device which disengages a sinker when it strikes bottom. The sinker is suspended 

 on a trigger, or tumbler, which is tripped when the bottom of the rod strikes bottom. 

 The sinker is then automatically detached. The detaching rod with sinker should be 

 used for all wire sounding in depths greater than 1,000 fathoms. (See also 4744.) 



The sinker is pear-shaped, specially cast. Drawings and specifications are available 

 for various sizes weighing from 35 to 110 pounds, although the size ordinarily used 

 weighs 65 pounds. This size^s about 8 inches in diameter at its widest point. A hole, 

 2K inches in diameter, runs vertically through the center, through which the detaching 

 rod is inserted. A wire ear or hook is cast on each side of the sinker slightly above the 

 middle, to which a wire sling is attached. The sinker is hung from the trigger of the 

 detaching rod by this wire shng. To decrease strain on the sounding wire and machine 

 the sinker is detached and left on the bottom. 



Another type of detaching weight for use with a snapper is described in 4761. 



467. Tide Gages 



A tide gage is an instrument for measuring the rise and fall of the tide. Tide gages 

 may be divided into two classifications — nom-egistering gages which requu-e an observer 

 to record the heights of the tide, and self-registering, or automatic, gages which auto- 

 matically record the rise and fall of the tide while unattended. Both types of tide gages 

 are fully described in Special Publication No. 196, Manual of Tide Observations. 



The Coast and Geodetic Survey uses two principal kinds of automatic tide gages 

 whic'h record the tide in the form of a graph. The standard automatic tide gage is 

 designed for use at primary tide stations, or at stations where observations are to be 



