4623 HYDROGRAPHIC MANUAL PaGE 386 



meiit to that effect, such as, "LeacUine tested correct to 15 fathoms," is sufficient. Where 

 it is found to be incorrect, the results of the comparison shall be entered under the appro- 

 priate headings, for each fathom, or for each 5 feet for a leadline marked in feet. The 

 true length by the standard is entered under the column headed "D" and the correspond- 

 ing length by leadline under the column headed "M." The corrections to the recorded 

 soundings are found by subtracting the leadline (M) values from the standard (D) values. 



Corrections must be entered in decimals of the same unit in which the leadline is 

 marked — e. g., for a line marked in fathoms and tenths of fathoms, corrections should be 

 in hundredths of fathoms ; for a line marked in feet, corrections should be in tenths of feet. 



A leadline should be re-marked when it is consistently in error by an amount larger 

 than that specified in 3111. 



4623. Errors in Leadlijie Soundings 



Errors in leadline soundings are of two general kinds; those resulting from an incor- 

 rect depth being indicated by the leadline, and those resulting from an incorrect reading 

 or recording of the depth. The hydrographer must be alert to keep both types of errors 

 at a minimum. 



Most inaccuracies of the first type result from a failure to have the leadline vertical 

 and taut at the time it is read. They can be largely eliminated by reducing the speed 

 of the vessel or by heaving the lead farther ahead. Similar errors result from sounding 

 with a leadline in strong currents (see 3464). An inaccuracy results from a failure 

 of the leadsman to raise the lead off the bottom and lower it again just before the 

 line is vertical. Errors sometimes result from the lead sinking into the ooze or soft 

 mud on the bottom. Unfortunately, all of these errors make the depths seem greater 

 than they actually are. (See also 3421.) 



Errors of the first type will also result from an incorrectly marked or graduated 

 leadline, or from a leadline which varies in length while being used in sounding. 



Errors of the second type are entirely personal, and conscientiousness and attention 

 on the part of the leadsman and recorder are the only remedies. 



The most common error is due to the recorder's misunderstanding the depth called 

 out by the leadsman. Some launch engines are noisy, and at times orders are being 

 issued or other data called out at the same time the leadsman calls out the sounding. 

 The leadsman should be instructed to call out all soundings loudly and distinctly, facing 

 the recorder as he does so ; and the recorder must repeat every sounding, for a check, as 

 he enters it in the Sounding Record. Such errors are usually due to a confusion 

 of similarly sounding numbers, such as 7 and 11,5 and 9, 15 and 50, etc. Careful 

 enunciation will eliminate such confusion. The -teen numbers should be equally 

 accented on both syllables, as fif -teen', but the -ty numbers should be strongly accented 

 on the first syllable only, as fif -ty. The first syllable of eleven should be strongly 

 stressed and prolonged, as ee' — leven,to distinguish it from seven in which the s should 

 be overemphasized, as ss — even. The v mji\e and the second n in nine should be 

 enunciated plainly. Wliere the leadsman and recorder, and at least one of the anglemen. 

 are bilingual, as in the Philippine Islands, the best assurance against such errors is to 

 have the depths called out in English and repeated by the recorder in Spanish, or 

 vice versa. 



Leadsmen should be instructed in heaving the lead and in reading the leadline; the 

 work of a new leadsman should be closely supervised until he is proficient. Close 

 attention to his duties will eliminate inaccurate readings. When an unexpected depth 

 is called out by the leadsman, the recorder should immediately ask that it be checked. 



Errors in soundings are also discussed in 774. 



