3. EQUIPMENT AND INSTRUMENTS 



71 



only and the other system fathoms and 

 tenths of fathoms. Every survey party that 

 has occasion to use both depth units in ac- 

 cordance with the instructions in this Manual 

 shall be equipped with at least one leadline 

 marked in each unit. 



Leadlines in fathoms shall be marked as 

 follows : 



Between the fathom marks intermediate 

 marks shall be placed, by which fractions of 

 a fathom can be read in tenths. Each half- 

 fathom (0.5) shall be marked by a seizing 

 of black thread and each even tenth-fathom 

 (0.2, 0.4, 0.6, and 0.8) by a seizing- of white 

 thread, the odd tenths being estimated. 



All fathom marks extend 2 inches from 

 the leadline. All the leather marks should 

 be made in one piece, the strips, about 14- 

 inch in width, being slit in the free end of 

 the mark. The bunting marks are made by 

 folding a piece of bunting to a size about 

 •VK-inch wide by 5 inches long; the length of 

 folded bunting is then folded once in the 

 middle and secured to the leadline so the 

 folded end is free. 



Waxed linen thread should be used to se- 

 cure the marks to the leadline. Marks should 

 be secured to the line so that there is no 

 possibility of their slipping, but the thread 

 should never be inserted through the braided 

 covering of the line. This is unnecessary if 

 the marks are properly secured and it is 

 almost impossible without mutilating either 

 the covering or the stranded wire core. All 

 marks should be secured so that their free 

 ends are up when sounding except 4-, 14-, 

 and 24-fathom marks. Marks so secured will 

 tend to stand out more from the line when 

 it is vertical. 



The toggle which the leadman grasps 

 when heaving the lead may be lashed on the 

 leadline or secured in a clove hitch of the 

 line. In the latter case the toggle must be 

 secured before the leadline is graduated. 



The lead to be used with the line, like- 

 wise, must be attached while the line is be- 

 ing graduated. 



Leadlines in feet shall be marked as 

 follows : 



Feet Marks 



2, 12, 22, etc Red bunting. 



4, 14, 24, etc White bunting. 



6, 16, 26, etc Blue bunting. 



8, 18, 28, etc Yellow bunting. 



10, 60, 110 One strip of leather. 



20, 70, 120 Two strips of leather. 



30, 80, 130 Leather with two holes. 



40, 90, 140 Leather with one hole. 



50 Star-shaped leather. 



100 Star-shaped leather with one 



hole. 



The intermediate odd feet (1, 3, 5, 7, 9, 

 etc.) shall be marked by white seizings. The 

 leathers marking the 10-foot multiples should 

 be identical in size with the fathom marks 

 used on a line marked in fathoms. The bunt- 

 ing marks identifying the intermediate even 

 feet should be slightly smaller in size. 



3-67 Verification of leadlines. — Lead- 

 lines used for sounding should be compared 

 with a standard at the beginning of a sea- 

 son and at frequent intervals thereafter 

 depending on the extent of their use. The 

 leadline should be wet and under a tension 

 equal to the weight of the attached lead in 

 water when tested. 



Rubber Stamp No. 35, Leadline Compari- 

 son, shall be used in recording results of the 

 comparison in the sounding record and shall 

 be recorded at the beginning or end of the 

 day's work (see 5-93 and 103). Where the 

 leadline is found to be correct, a statement 

 to that effect is sufficient. Where it is found 

 to be incorrect, the results of the comparison 

 shall be entered for each fathom, or for each 

 five feet for a leadline marked in feet. The 

 true length by the standard is entered in the 

 column headed "D" and the corresponding 

 length of leadline under the column headed 

 "M." The corrections to leadline soundings 

 are obtained by subtracting the leadline 



