6. THE SMOOTH SHEET 



6-1 Definition and purpose. — A smooth 

 sheet is the final, carefully made plot of a 

 hydrographic survey. In contrast to the boat 

 sheet, which is a work sheet plotted during 

 field operations from preliminary field data, 

 the smooth sheet is plotted from corrected 

 data and conforms with more rigid carto- 

 graphic standards which are described in 

 this chapter. 



After registry, verification, and review in 

 the Washington Office, the smooth sheet be- 

 comes the official permanent record of that 

 particular survey and is the principal au- 

 thority for hydrographic data to be charted. 

 The boat sheet is usually discarded after final 

 administrative approval of the survey. 



6-2 Smooth sheet paper. — Smooth sheets 

 shall be prepared only on first-quality white 

 drawing paper mounted on muslin furnished 

 by the Washington Office in flat sheets. 

 Plastic and aluminum mounted sheets are 

 widely used in various activities, but they 

 shall not be used for smooth sheets unless 

 specifically authorized in project or other 

 instructions. 



Factors which control selection of suit- 

 able smooth sheet material are: minimum 

 dimensional change (distortion), absence of 

 surface imperfections, reception to inking 

 particularly after erasure, toughness of a 

 moistened surface, and pliability. Samples of 

 smooth sheet stock are subjected to test be- 

 fore a shipment is accepted, however, con- 

 siderable variation in the quality of smooth 

 sheet paper is found even in the same ship- 

 ment. If the paper is found to be unsuitable 

 for smooth sheet plotting, the Washington 

 Office should be notified of the particular 

 fault or faults. The trade name of the paper 

 and the date of receipt should be stated if 

 these are known. 



The most troublesome characteristic of 



muslin-mounted paper is the uneven distor- 

 tion which occurs with changing tempera- 

 ture and humidity. Uniform distortion of a 

 sheet presents no serious problem, but ac- 

 ceptable distortion should never be as much 

 as 0.5 percent, and greater distortion is con- 

 sidered excessive. Although the best quality 

 of smooth sheet paper is manufactured so 

 that the percentage of contraction or expan- 

 sion is nearly equal in all directions, tests 

 have shown that distortion across the width 

 of the paper usually is greater than for an 

 equal distance lengthwise of the paper. The 

 inequality of distortion in the two dimensions 

 should not be as much as 0.25 percent. 



In all plotting the amount of distortion 

 should be determined and checked from time 

 to time. Distortion should be compensated 

 for as much as possible. In some instances 

 it may be necessary to defer plotting until 

 an unequally distorted projection returns to 

 within reasonable limits. 



Tracing cloth shall be used when it is ad- 

 visable in a congested area to smooth plot 

 supplemental hydrography separately for in- 

 sertion in the descriptive report. 



6-3 Smooth sheet sizes. — The standard 

 size of a smooth sheet is 36 by 54 inches 

 which shall not ordinarily be exceeded (see 

 1-8 and 2-22). Although sheets are fur- 

 nished in 60-inch lengths, they should be 

 trimmed to 54 inches unless the increased 

 length is needed for plotting the control. 

 When the entire sheet is not needed for the 

 survey, any excess length over 8 inches at 

 either end of the sheet should be trimmed 

 off; however, the minimum dimension of the 

 sheet shall not be less than 30 inches. 



When oversize sheets are required to plot 

 the sheet at the scale of the survey, con- 

 sideration should be given to using a smaller 

 scale as explained in 6-7. 



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