Page 737 the smooth sheet 7826 



should be used and not "uncovers 2 ft at LW"-. Bare rocks should be referred to mean 

 high water (MHW) and rocks awash to the sounding datum (MLW, MLLW, or MLWS), 

 except that rocks awash at mean high water should be so designated (see 7823). Eleva- 

 tions above any datum should be given in feet to the nearest whole foot. Descriptions, 

 such as "breaks at half tide", "breaks in heavy weather only", and the like, are of 

 value for charting and should be shown on the smooth sheet wherever the information 

 has been obtained. Judgment is required in the selection and proper placement of 

 notes in order to avoid crowding the sheet with a multitude of unimportant notes, 

 but no important danger should ever be shown by symbol alone. 



a. Bare rocks. — The elevations in feet of bare rocks should be shown by slanting figures, in paren- 

 theses, close to the feature. If they originate with the topographic survey they shall be shown in red, 

 otherwise in pencil to be subsequently inked in black in the Washington OflRce. (See also 755 and 782.) 



b. Rocks awash. — Elevations of rocks awash above the sounding datum may be indicated either 

 by notes, such as "uncovers 2 ft at MLW" or by slanting figures alone, in parentheses and under- 

 scored, as for example (S). (See part "O" of the Symbols and Abbreviations chart, fig. 189, part IX.) 

 If awash at the sounding datum or at mean high water, a note such as "awash at MLLW" should 

 be used. No rigid rules need be followed, however, in the use of one form or the other. It is left 

 mostly to the discretion of the smooth-sheet plotter. Generally, however, it is desirable to use notes 

 in the case of isolated rocks, or for the highest rock in a group of offshore rocks, or for the outermost 

 rock of a number of alongshore rocks. In congested areas or for the many less important rocks the 

 underscored figure should be used. 



c. Reefs and ledges. — The above considerations also apply to the notes and elevations of reefs 

 and ledges above the sounding datum or to the rocks awash in a generally submerged reef or ledge. 



7826. Rocky Areas 



Where, owing to heavy seas, low tide, draft of vessel, etc., it has been impossible 

 to sound in an area witli a rocky bottom, but which is otherwise clear of rocks, the 

 approximate danger limit should be indicated by a line of sunken-rock symbols. 



Where, owing to a multitude of scattered rocks, it is needless to sound in an area, 

 the positions of the off -lying rocks should be determined and the unsounded area should 

 be marked "foul — unsurveyed". (See also 7824.) 



Wliere large areas, unimportant for navigation, have not been thoroughly surveyed, 

 as where thick beds of kelp border the shore or where an extensive foul area exists in a 

 remote locality, the outer limits should be shown on the smooth sheet and an appropri- 

 ate legend added inside. For kelp, the symbol should be used and the area should 

 contain the legend "heavy kelp, not navigable, not thoroughly surveyed". For a foul 

 area, a dash line should be used enclosing the legend "foul, not thoroagldy surveyed". 

 (See 36236 and 367.) 



7827. Reconciliation of Topographic and Hydrographic Data 



As is noted in 75, discrepancies between the topographic and hydrographic surveys 

 as to the location and character of rocks should be harmonized in the field by a further 

 examination if necessary, and all differences reconciled in the Sounding Records, on the 

 sheets, and in the Descriptive Reports before submitting the survey to the Office. 



Where it is not feasible to investigate the discrepancies further, or to consult the 

 topographer, the smooth-sheet plotter should then evaluate all the information available 

 from both sources, taking into consideration the strength of the position determination, 

 the proximity of the surveyor to the feature, the stage of the tide, etc., and resolve the 



