3352 HYDROGRAPHIC MANUAL PaGE 226 



be obtained at the time of slowing down, the same course should be maintained, and 

 at the end of the line the distance from the high-water line should be estimated. One 

 angle, or a bearing, can often be obtained and combined with the dead reckoning to 

 provide a more accurate position than can be obtained by estimation (see 7625). 



Along an irregular coast it is impracticable to provide a sufficient number of 

 signals to fix the beginnings and ends of lines in all of the small bights and indenta- 

 tions into which lines should be run. An estimated distance to the high-water line or 

 distances and directions to irregularities in the shoreline will provide sufficient control. 



3352. Curved Sounding Lines in Winding VTateruays 



In narrow winding waterways it is often impracticable to provide a sufficient num- 

 ber of signals from which to fix the position of the sounding vessel frequently enough 

 to define its exact course. The sounding lines frequently parallel the shore and where 

 the course of a narrow stream is winding, the hydrographer must fix his position with 

 reference to control stations when practicable, at other times estimating positions with 

 reference to the adjacent shoreline features and from his sense of dead reckoning. 

 The sounding lines must frequently conform to the curves of the shoreline, even between 

 fixed positions where it is impracticable to run a straight course from one position to the 

 next. The hydrographer must estimate the course and position of the sounding 

 vessel, plotting this course on the boat sheet from estimated distances and dead reckon- 

 ing. In such cases notes should be made in the Sounding Record that the courses 

 between fixed positions are not straight and direct, and that they should be taken from 

 the courses sketched on the boat sheet. 



Such a lack of control is authorized only where the waterway is unimportant, 

 its average width is less than 200 meters, and the establishment of the required control 

 would be exceedingly uneconomic. The lack of fixed positions should be compensated 

 foi; by additional positions referenced to natural features and most complete notes in 

 the Sounding Record, but irrespective of this, the smooth plotter will have to rely on 

 the boat sheets to an unusual degree for the positions of the sounding lines. 



3353. Distances to Objects Abeam 



The hydrographer must note in the Sounding Record the distance each object in 

 the water area is passed close abeam. The distance should be referenced to the sound- 

 ing line or lines that pass nearest the object. Such distances should be measured by 

 depression angle (see 3362), when this is practicable, rather than be estimated. The 

 exact height of eye must be recorded in the Sounding Record, together with the depres- 

 sion angle. Among objects to which this applies are navigation and survey buoys, 

 rocks (sunken, awash, and bare), isolated clumps or streamers of kelp, piles or fish stakes, 

 and in fact any fixed or anchored object which may be a danger or an aid to 

 navigation . 



It is very disconcerting in plotting the smooth sheet or in chart compilation to 

 find that the hydrographic party has passed close to an. object of the nature described 

 above without mentioning it in the Sounding Record. Some doubt is raised as to its 

 actual existence, or whether it was visible at the time of passing. 



Such data are intended to verify the existence and positions of such objects and 

 should never be substituted for a more accurate means of location, when such is prac- 

 ticable. 



