7845 HYDROGRAPHIC MANUAL PaGE 742 



It is particularly important that the elevations of landmarks be known both 

 above the ground and above mean high water, and the legends must make these eleva- 

 tions clear. They are necessary for the charts and for the Coast Pilot. 



7845. Ranges, Bearings, and Sailing Lines 



All ranges, bearings for clearing dangers and other purposes, and recommended 

 sailing lines on courses or ranges, shall be shown on the smooth sheet in pencil where 

 they have been determined by the hydrographic party, and the following symbols 

 shall be used : A range shall be shown as a broken line of short equal dashes ; a bearing 

 shall be shown as a dotted line; and a recommended sailing line shall be shown as a 

 continuous line broken at irregular intervals so as not to be drawn through soundings 

 (see fig. 169). It should be noted that that part of a range line which is to be followed 

 by a vessel is a sailing line and should be so symbolized. The objects wliicli determine 

 the ranges or to which the bearings apply shall be correctly shown and identified, and 

 the names of the objects a.nd the purpose of the range or bearings indicated in pencil 

 along the lines. (See 356.) 



Where a range (indicated by brackets in the Light List) formed by two lights or 

 by two beacons, is located within the limits of the survey, there are specific instructions 

 for the determination of its azimuth by the survey party (see 3833). Only if the 

 azimuth has been determined by the hydrographic party shall this line be show^n on the 

 smooth sheet. The instructions for such locations call for obtaining strong sextant 

 fixes on the range at a sufficient distance from the front range mark to produce a long 

 azimuth line for accurate scaling. In the case of ranges established at an entrance for 

 use in crossing a bar, a sextant fix should be obtained on or outside the bar. These 

 fixes are indexed in the Sounding Records and must be plotted accurately on the smooth 

 sheet. From these plotted positions the ranges are penciled. The azimuths are then 

 scaled by protractor and noted in pencil along the range lines. 



7846. Overhead Clearances 



Bridge clearances and the clearances of overhead cables are important to naviga- 

 tion and should be shown on the smooth sheet for the information of the chart com- 

 piler. They should be left in pencil by the field party. 



a. Bridge clearances. — The vertical and horizontal clearances should be given for 

 all bridges over navigable waters if such information has been obtained (see 3836). 

 Where a discrepancy exists between the field data and the data given in the "List of 

 Bridges Over the Navigable Waters of the United States," published by the United 

 States Corps of Engineers, the field data should be given on the smooth sheet, but 

 attention should be called to the discrepancy in the Descriptive Report (see 842P), 

 The notation on the smooth sheet should include the name of the bridge, if it has one; 

 the type of bridge, whether fixed, draw, etc.; the horizontal clearance in feet; and the 

 vertical clearance in feet above mean high water. The note should be in the form shown 

 in figure 17L 



b. Overhead cables. — The locations of all overhead cables, transmission, telephone, 

 or telegraph, over navigable waters shall be shown on the smooth sheet by dash pencil 

 lines in a manner that will interfere least with the plotted soundings. The note on 

 the smooth sheet should state "overhead cable" and should give the clearance in feet 

 at mean high water (see fig. 171). 



