324 HYDROGRAPHIC MANUAL PaGE 208 



speed scales described in 4826. These may be inked on the boat sheet in spaces where 

 no sounding is expected. 



324. Use of Boat Sheet During Survey 



It is frequently not practicable to handle the boat sheet as carefully as one would 

 handle a smooth sheet, nor is it necessary. The boat sheet is unavoidably subjected 

 to somewhat rough treatment, especially in launches and small boats, but it should not 

 be treated carelessly. The more carefully it is handled, the better will it retain its 

 original dimensions aind accuracy, and the more useful will it be as a guide in plotting 

 and verifying the smooth sheet. 



It is essential, however, that the best possible care be taken of an R.A.R. boat 

 sheet for reasons mentioned in 3223. 



A boat sheet should not be rolled to a diameter smaller than 3 inches. 



3241. Proposed Sounding Lines 



To survey an area thoroughly and effectively, systematically planned lines of 

 soundings must be run. The desu-ed system is usually indicated in a general way in 

 the project instructions, but if not, it should be planned in accordance with 314. The 

 proposed sounding lines of the general system are ruled in pencil on the boat sheet as 

 a guide to the hydrographer; only a few lines, however, should be ruled in advance 

 because, as the survey progresses and additional Imowledge is acquired of the depths 

 in the area and of the character of the submarine relief, it may be necessary to shift the 

 entire system slightly from time to time or to adopt a different spacing of lines. 



Where the use of ranges is practicable, proposed lines can usually be followed very 

 closely. In other cases the sounding vessel, can often be kept only approximately on 

 the proposed lines, especially where there are strong irregular currents or where the 

 control is relatively weak. Thus two adjacent sounding lines frequently deviate from 

 the proposed lines to such an extent that a split line is required to comply with the 

 spacing requirements. 



Additional lines which split the specified spacing, or lines of a superimposed system 

 in an entirely different direction, are usually laid out on the boat sheet to guide the 

 development of extensive shoal areas encountered during the survey. 



3242. Proposed Development 



Every shoal indication disclosed by the systematic sounding lines (see 3154) 

 should be emphasized on the boat sheet by encircling the area with a red pencil, or other- 

 wise, as a reminder that further investigation or development is required. As the 

 soundings are inked during the progress of the survey, all danger indications and sound- 

 ings wliich are suspected of being in error should likewise be noted for further develop- 

 ment or investigation (see 3621). The least depths on shoals found by prior surveys 

 and areas in which dangers or shoals have been reported, or are suspected, should be 

 similarly marked in color for future attention. 



3243. Plotting Positions 



The principal use of the boat sheet is, of course, to enable the hydrographer to 

 plot each position of the sounding vessel as the observations are made; to determine 

 whether on line or not, and if not, to indicate the change in course required. As the 

 consecutive lines of the system are surveyed and the soundings are plotted, the results 



