Page 205 hydrography 3222 



colored paper has been found most satisfactory to reduce the glare of the reflected 

 light. A 100-percent rag paper, of comparatively smooth surface and heavy weight, 

 mounted on the best grade of cotton sheeting is required. Boat-sheet paper is pur- 

 chased by the Federal Government in accordance with standard specifications. The 

 makes of paper complying with these specifications are subject to change from year 

 to year. The General Schedule of Supplies should be consulted for the make of paper 

 available at any given time. 



When accuracy of plotting is an important factor, as in Radio Acoustic Ranging 

 (R.A.R.), the paper recommended for smooth sheets should be used for boat sheets 

 (see 711). 



3222. Boat- Sheet Limits 



The limits of a boat sheet will ordinarily be the same as the corresponding smooth 

 sheet, eycept that a wider margin of spare paper is usually allowed for unforeseen con- 

 tingencies and because the edges are likely to become cracked and worn in use. Occa- 

 sionally after the survey has been completed, it will be found that the smooth sheet can 

 be laid out more economically by not adhering exactly to the limits of the boat sheet. 



The boat sheet need not necessarily contain within its limits the entire area to be 

 covered by a smooth sheet. For convenience, the area may be divided and included on 

 two or more different boat sheets, each of which shall bear the same survey number as 

 the smooth sheet. Even if the entire area is included on one boat sheet, copies of it 

 may be utilized if two or more hydrographic units are to survey simultaneously in the 

 area, and all copies should bear the same survey number as the smooth sheet. (See 

 3213.) 



A boat sheet shall not be laid out purposely to include an area, the survey of which 

 will subsequently be plotted on two smooth sheets. 



3223. Accuracy of Construction 



The accuracy to be used in the construction of a boat sheet depends somewhat on 

 the scale and the strength of positions to be expected in the area, and on the exposure 

 to which the boat sheet will be subjected during use. For boat sheets used in R.A.R. 

 surveys, the best quality of paper should be used and the accuracy of construction and 

 subsequent care should be comparable to those required for smooth sheets. Accuracy 

 of construction and care during use are important since all the distance circles cannot 

 be drawn at the time of construction, as on the smooth sheet (see 734). By contrast, 

 a large-scale boat sheet for an inshore hydrographic survey, where the control stations 

 are always comparatively near, may be constructed with less accuracy, especially since 

 it is likely to get wet from spray in rough weather and be subjected to other hard usage 

 during the progress of the survey. 



3224. Methods of Construction 



The boat sheet may be constructed by methods similar to those used in constructing 

 a smooth sheet, and if this is done the same general care and accuracy shall be used in 

 its construction (see 73 and 74). If there is a corresponding topographic survey on 

 the same scale, it may be used for transferring by tracing paper (see 7561) the projec- 

 tion, control, and all necessary details to the boat sheet. The projection intersections 

 and control points should be pricked on the tracing with a fine needle point and trans- 

 ferred to the boat sheet in a similar manner. It is well to preserve these tracings, if 

 they are carefully made, for possible use in making the smooth hydrographic sheets. 



