6. THE SMOOTH SHEET 



213 



shall not be used over the letter i or as 

 punctuation in the water area. 



6-42 Protective overlay sheet. — After 

 the advance work on the smooth sheet has 

 been completed and checked, preparatory to 

 plotting hydrographic data, the sheet shall 

 be covered by a protective overlay. This will 

 prevent soiling the sheet when using pro- 

 tractors or templates, and accumulation of 

 dust. Thin white tracing paper, tracing 

 cloth, or clear plastic sheets may be used for 

 this purpose. One edge of the overlay should 

 be folded over the top edge of the smooth 

 sheet and secured to the back of the sheet 

 by cellulose tape or it may be held in place 

 by paper clips if they do not interfere with 

 movement of the protractor. Thumb tacks 

 shall never be put through the smooth sheet. 

 Several tick marks at intersection of projec- 

 tion lines should be drawn on the overlay 

 sheet for purposes of registration. 



When positions are to be plotted by three- 

 armed protractors, a small round hole slight- 

 ly larger than the station symbol shall be 

 cut in the overlay sheet and over each sta- 

 tion exposing the center points for greater 

 accuracy in plotting. This can be done with 

 a sharp pointed bow spring divider or a 

 punch of appropriate size. A protective back- 

 ing of wood or heavy plastic should be used 

 to prevent damage to the smooth sheet or 

 plotting table. 



Circle sheets should be covered by a sheet 

 of very thin plastic and positions pricked 

 with a sharp point. These positions may be 

 plotted directly on the smooth sheet if the 

 protractor and other tools are kept clean and 

 unused parts of the sheet covered. 



When plotting the soundings sections of 

 tracing paper should be used to protect the 

 smooth sheet exposing part of the sheet 

 where soundings are being plotted. Exces- 

 sive sliding of the paper over penciled sound- 

 ings may cause graphite smears, especially 

 when relatively soft pencils are used. 



A waterproof cover should be placed over 

 the plotting table during off-duty hours and 

 it is advisable to place a caution sign on ta- 

 bles where smooth sheets are left. 



6-43 Use of boat sheet. — If the smooth 

 sheet is to be plotted by an individual other 

 than the one who was in immediate charge 

 of the survey, the hydrographer's report and 

 the boat sheet should be examined for any 

 information which may affect the plotting 

 before proceeding with the smooth plot. The 

 position or classification of control stations 

 may have been affected by supplemental ob- 

 servations. The sounding volume index 

 should be examined for information perti- 

 nent to the control in order to avoid later 

 replotting because of a revised position of a 

 hydrographic station. Also, the transfer of 

 certain explanatory notes from the boat 

 sheet to a corresponding position on the over- 

 lay may clarify subsequent confusion during 

 smooth plotting due to twin objects or other 

 control problems, names, or other vagaries 

 of survey work on the water. 



The boat sheet is invaluable as a guide 

 for smooth-plotting the sounding-line courses, 

 individual positions, and features (see 5-4). 

 The hydrographer sees and plots conditions 

 which may inadvertently be recorded in er- 

 ror or may not be recorded at all. He might 

 see an object to port and plot the line ac- 

 cordingly, yet unthinkingly call starboard to 

 the recorder or not report at all. He might 

 survey an inshore line by running parallel 

 to the beach or by running straight lines 

 from point to point and show the courses 

 properly on the boat sheet without either of 

 the alternative courses being recorded. There 

 are many other instances of boat sheet guid- 

 ance. Each circumstance shall be evaluated 

 from all available information. 



6-44 Development overlays. — Overly con- 

 gested hydrography sometimes results from 

 necessarily persistent sounding over a reef, 

 shoal, or obstruction and in a constricted 

 passage or in areas adjacent to waterfront 

 structures. All lines required to position 

 the least depth and define bottom configura- 

 tion by depth curves shall be plotted on 

 the smooth sheet (see 5-25). Subplans are 

 sometimes used to plot the hydrography and 

 other detail at a large scale. Supplemental 

 overlays plotted on tracing cloth may be 

 used where necessary to avoid congested 



