226 



HYDROGRAPHIC MANUAL 



and day letter, and the clearance depth 

 obtained. 



Where a contemporary wire-drag survey 

 has been made by another survey party, all 

 drag finds, groundings and clearances will be 

 transferred to the smooth sheet in green ink 

 after office verification of both surveys. 



6-69 Submerged obstructions. — A vari- 

 ety of submerged obstructions is encountered 

 in hydrographic surveying, all of which must 

 be shown on the smooth sheet. Where least 

 depths are not obtained on unnatural fea- 

 tures such as stubs of piles, ruins of piers 

 or other structures, wreckage of various 

 kinds, they shall be shown by a 1-mm circle 

 or dashed outlined, in pencil and described. 

 If the nature of the obstruction was not 

 determined, the note "obstr" shall be used. 

 Dashed lines shall be used to indicate the 

 extension below high water of marine rail- 

 ways, groins, breakwaters, outfall sewers, or 

 other unnatural features rising above the 

 bottom. 



6-70 Breakers, tide rips, eddies. — The 



limits of breakers, whether offshore or 

 alongshore, should be shown by a dash line, 

 in pencil, with the notation "breakers" added 

 (Fig. 79). Where cuts are taken to break- 

 ers at sunken rocks or rocks awash, their 

 intersection should be indicated by the ap- 

 propriate rock symbol. 



Tide rips occur in places where strong 

 currents are found and are usually encoun- 

 tered in the vicinity of shoals or where the 

 bottom is uneven. Small areas of tide rips 

 may be shown by symbol or by legend. Where 

 the feature is extensive the approximate 

 limits should be outlined with dashed pencil 

 lines and an appropriate descriptive note 

 added. Tide rips should be qualified as heavy, 

 moderate, or light. 



Where current eddies are observed they 

 should be shown on the smooth sheet by 

 symbol or legend. 



6-71 Tide and current stations. — Loca- 

 tions of tide and current stations shall be 

 shown by blue circles 3 mm in diameter, 

 without center dot, and legend (Fig. 79). 

 The location of oceanographic stations or 



current observations by drogues shall not 

 be shown on the smooth sheet. 



6-72 Geographic names. — The final se- 

 lection and placement of geographic names 

 shall be made in the Washington Office after 

 review and approval of the names list by 

 the Geographic Names Section (see 7-13). 

 Names of hydrographic features and a few 

 topographic features shall be penciled on the 

 sheet by the smooth plotter. Geographic 

 names shall not be added to the smooth sheet 

 until the soundings and other hydrographic 

 data have been plotted. They should be 

 placed so as to indicate clearly the features 

 designated. 



Geographic names must not obscure or 

 confuse the soundings. On an inshore hy- 

 drographic survey, it is generally necessary 

 to place all names inside the high-water line. 

 Where names must be lettered in the water 

 areas, particularly in very congested areas, 

 a judicious placement of the name and spac- 

 ing of the letters will often avoid obscuring 

 soundings and other details. 



Since the smooth sheet is the authority for 

 charting names of all features at and offshore 

 from the high-water line, extreme care shall 

 be taken in the spelling and placement of 

 the names. Instructions for lettering names 

 will be found in 6-14. The published charts 

 are excellent guides for placement of names 

 and relative size of lettering for various 

 features. 



6-73 Adjoining surveys. — After the 

 smooth sheet is completed a comparison 

 shall be made with adjoining, contemporary 

 surveys to determine the completeness and 

 relative agreement of hydrography. Any 

 consistent differences in soundings and cor- 

 responding displacement of depth curves, as 

 well as gaps in coverage, shall be stated in 

 the descriptive report (see 7-4J). This part 

 of the report is of significant value when the 

 unverified survey is used for preliminary 

 revision of the chart and is considered when 

 assigning verification priorities. Soundings 

 shall not be transferred to the smooth sheet 

 by the smooth plotter. 



In the event an adjoining survey is in- 



