3541 HYDROGRAPHIC MANUAL PaGE 272 



The specified system of sounding lines is based on an expected type of submarine 

 topography and where Unexpected irregularities are disclosed the spacing must be 

 reduced in these areas. 



Harbors and anchorages are ordinarily surveyed at larger scales and with a closer 

 spacing of soundmg lines than is specified for the general area. Additional sounding 

 lines shall be run in any bight or indentation in the coast in which a vessel might an- 

 chor, even though a larger scale is not specified nor is deemed necessary by the Chief 



of Party. 



3541. Holidays 



No holidays should be left in the hydrographic survey. A holiday is not likely 

 to occur within the area of systematic sounding lines on one survey sheet but it may 

 occur at junctions with prior surveys, at junctions between surveys on different scales 

 or by different sounding units, and sometimes where a change is made in the spacing 

 of the lines. Before leaving the working ground, and in the case of buoys before re- 

 moving them from their positions, the Chief of Party must assure himself that no 

 holidays have been left in the project area which might necessitate a return to the area 

 or the reestablishment of expensive control. 



3542. Missed Soundings 



No bottom leadline soundings are not satisfactory and if they cannot be avoided 

 in important areas, definite measured depths must be obtained later. Where such 

 soundings occur near the outer limits of an area due to the general depths being too 

 great for the method of measurement, the area surveyed on the adjacent sheet by other 

 methods must overlap to a junction with definite soundings. 



Echo soundings are sometimes missed because the apparatus is not functioning 

 properly or because the conditions prevent the echo from bemg received. In important 

 areas where soundings are missed because of improper functioning of the apparatus, 

 the line should be repeated at a later time and additional soundings taken. In other 

 cases they need not be repeated except where consecutive misses along a sounding line 

 (jreate a gap longer than the space between adjacent lines. 



In deep water, when the apparatus is functioning properly and no echo can be heard, 

 one additional attempt shall be made to obtain the soundings at a later date, and if this 

 is not successful, the area may be omitted if of not too great an extent. If of large 

 extent, wire soundings should be taken. 



Each ti^ne that echo soundings are missed the reason therefor shall be stated in the 

 "Remarks" column of the Sounding Record. 



When the echo-soundmg apparatus intended for use in deep water repeatedly 

 fails in such depths the Washmgton Office shall be notified in a report containing all 

 the facts and the supposed reasons therefor. 



355. Development 



A. great responsibility rests on the modern hydrographer. Vessels of great size 

 and value aavigate areas with a minimum depth of water under their keels, trusting 

 implicitly in the charts to avoid dangers. The possibility of the loss of or damage to 

 a vessel by striking some uncharted danger must always be borne in mind b}' the 

 hydrographer. It is only by a close spacing of soundings and sounding lines and a 

 thorough examination of all irregularities of the bottom that there can be anv reasonable 

 assurance of the completeness of a survey. 



