Page 713 the smooth sheet . 7682 



until after the soundings have been penciled, and certainly they must not be inked in a 

 given area until after all of the positions have been plotted in that area, in order that 

 they may be so placed as not to conflict with the soundings on other lines. Under any 

 circumstances the placement of the position numbers and day letters must indicate in- 

 dubitably the positions to which they refer. This may be accomplished where necessary 

 by the use of fine inked arrows or leaders from the position number to the position dot, 

 using the same color as for the number. 



7682. Connecting Positions 



Successive positions shall be connected by a pencU line using a well-sharpened 

 3H or 4H pencil with a round point — not a chisel edge (see 724). Care must be taken 

 not to engrave this line in the surface of the paper. ^ 



The connecting lines represent the path of the survey vessel, and in drawing them 

 on the smooth sheet the path should be assimilated so far as possible. Both the boat 

 sheet and the entries in the Sounding Record as to changes in course should be used as 

 a guide. Instructions for the field survey require that a position be taken at each change 

 in course greater than 10° (see 3463). However, it is frequently necessary to make 

 changes in course between positions, which are large enough to affect the locations of 

 the soundings between the positions. Changes in course of 1° or 2° between positions 

 may be disregarded in the plotting and the consecutive positions connected by a straight 

 line, but for greater changes the positions should be connected by lines which follow 

 the actual track of the vessel. 



Changes m course are not always effective at the time of the order to change. 

 This depends on the momentum of the vessel. In a launch the effect is almost immedi- 

 ate, while in the larger vessels, some time elapses before the change becomes effective. 

 This fact together with a knowledge of the turning radius of the vessel will determine 

 its path. 



Each vessel has its own turning radius, being proportionately larger as the size of 

 the vessel increases. When better information relative to the turning radius is lacking, 

 it may be assumed to be, as a general rule, zero for outboard motor boats, 15 meters for 

 the smaller launches, and 150 meters for the smaller vessels. For the larger ships, unless 

 there is evidence to the contrary, turns should be plotted on the assumption that, after 

 a position, the vessel maintains the original course for twice the distance it is on the 

 new course before the next position is taken (see 3463). If soundings on turns are to be 

 inked on the smooth sheet, the greatest care must be taken in correctly representing 

 the turns. This is particularly true in the case of right-angled and 1 80° tm-ns. However, 

 where no soundings have been recorded, only the approximate path need be indicated. 



Minor changes in course are frequently made by the hydrographer after a position 

 has been plotted on the boat sheet and it is learned what change is necessary. Obviously 

 such changes occur some little distance past the position, although the recorded data 

 may not so indicate. In such cases, if no change in course has occurred between the 

 two immediately preceding positions nor between the two succeeding positions, the 

 connecting lines between these may be extended forward and backward and their inter- 

 section will usually represent the point where the change in course was effective. 



In narrow winding channels and rivers and sometimes on the inshore line along a 

 rugged coast, it is impracticable to take a position at every turn, since the sounding 

 lines must follow the bends in the shoreline. In such cases the connecting lines must 

 be transferred from the boat sheet, on which the hydrographer will have indicated the 

 correct track. (See 3352.) 



