7752 



HYDROGRAPHIC MANUAL 



Page 728 



Enlarged subplans, such as those to include the water area of a small bay, bight, 

 inlet, or anchorage area, shall be surrounded by a heavy margin in black ink. Each 

 subplan must include the scale, the name of the water feature, if any, and at least one 

 meridian and parallel. An arrow should be added leading to the plan from that part 

 of the smooth sheet of which the plan is an enlargement, where it can be done without 

 interference with the hydrography. A fine dash pencil line should be drawn around the 

 area on the original scale which has been enlarged. Details shown in the enlargement 

 may be omitted from the original scale. Wherever practicable, the subplan should 

 be located so that its meridian and parallel coincide with two of the lines of the prin- 

 cipal projection. (See fig. 165.) 



Where soundings are taken in small docks and along the sides and ends of small 

 piers and are located by reference distances to or along the piers, enlarged plans of these 



Scale 1:5,000 float e' x 4o' 



Scale 1:2,500 



Figure 166. — Subplan of pier with soundings alongside. 



shall be shown as nearby as convenient to the areas at the original scale. If the enlarged 

 plan cannot be shown adjacent to the area, there shall be an arrow leading to the 

 enlarged pier from that place on the shoreline where the pier is located. Such plans 

 need not contain a scale nor be surrounded by a margin. Each plan, shall show in 

 figures the principal dimensions of the pier. (See fig. 166.) 



7752. Overlay Tracings 



Where the subplan method is impracticable, because of the extent of the area 

 involved, or for any other reason, overlay tracings shall be used. These are plottings on 

 tracing cloth, at the scale of the smooth sheet, of one or more of the several systems of 

 sounding lines used to develop the area. In order to achieve clarity, it is sometimes 

 necessary to use more than one overlay. The overlays need be only large enough to 

 include the hydrography in question, and need not cover the entire sheet. The pro- 

 tracting is done directly on the tracing using the control points on the smooth sheet. 

 Both positions and soundings on the overlay shall be inked (positions in black and 

 soundings in red) . 



Each overlay tracing shall be referenced to the smooth sheet by number as "Over- 

 lay to accompany H-5236," and shall be marked by a sufficient number of projection 

 intersections, at least two of which shall be identified by their latitudes and longitudes. 



Smooth-sheet plotters may determine where overlay tracings are necessary and 

 what portion of the work should be so prepared by the criterion that it must be possible 

 for the verifier to identify each position on the various sounding lines. As a general rule, 

 where the sounding lines are not much less than one-fourth inch apart, two systems of 

 lines may be satisfactorily plotted directly on the smooth sheet, but where there are 



