128 (Change 1) 



HYDROGRAPHIC MANUAL 



not pencilled until the survey is complete, 

 since movement of the cover sheet can pro- 

 duce undesirable graphite smears on the 

 smooth sheet. 



The boat-smooth sheet method of plotting 

 a survey affords a real saving since only one 

 projection is required and it is not necessary 

 to plot positions a second time. The method 

 is not restricted to use with electronic control 

 systems. Chiefs of party should use this 

 method of plotting whenever it is practicable. 



5-6 Construction of boat sheet. — Boat 

 sheets are constructed to cover specific areas 

 as shown on the approved sheet layout (see 

 2-20). Boat sheet paper will be furnished 

 by the Washington Office in flat sheets 36 

 by 60 inches or 42 by 60 inches (see 1-9). 



The projections are constructed in accord- 

 ance with instructions contained in Special 

 Publication No. 5 (see 1-12). A layout 

 sketch of the projection with distances in 

 meters appropriate to the scale noted thereon 

 should be made and checked before the pro- 

 jection is constructed. The layout may be 

 retained for later use in constructing the 

 smooth sheet projection. Although a boat 

 sheet is subject to considerable distortion by 

 rough use and exposure during progress of 

 a survey, the projection should be accurately 

 constructed and verified. See Table 1 for 

 projection line intervals. 



The projection should be constructed and 

 checked the same day. The dms. and dps. 

 of control stations should be plotted and 

 checked as soon as possible. When electronic 

 control is to be used, the distance circles 

 should be drawn if the station locations are 

 known (see 5-11). The projection is then 

 inked in fine full lines about 0.15 mm wide. 



Stamp No. 42, Hydrographic Survey (Fig. 

 50), shall be impressed in the lower right- 

 hand corner and entries made in all ap- 

 plicable spaces. The initials of the persons 

 plotting and verifying each item should be 

 entered, together with the dates. 



5-7 Projection template. — A template on 

 Mylar, a very stable plastic, has been devised 

 to facilitate construction of boat and smooth 

 sheet projections. Nine points are marked 

 on the template so that construction lines 

 may be quickly and easily drawn. The con- 

 struction procedure is as follows: 



(a) Locate the center of the projection 

 on the sheet. This is the intersection of the 

 central meridian and parallel. 



(b) Place the template on the sheet with 

 the central point over the center of the pro- 

 jection and orient the template as required 

 by the layout. 



(c) Prick all nine points on the sheet and 

 check the long diagonals to prove the per- 

 pendicularity of the construction lines. 



(d) Draw pencil lines through the points 

 in a north-south direction. The center line 

 is the central meridian. 



(e) Draw the central parallel construction 

 line through the three points in the east- 

 west direction. 



(f) From line (e) set off the distances 

 on lines (d) to the most northerly and south- 

 erly parallels and draw them. 



(g) From the central meridian set off on 

 lines (e) and (f) the extreme east and west 

 meridians and draw them. 



After the curvature values have been ap- 



No 42 HYDROGRAPHIC Survey 



Field Uo^A../Q.:3r.'$.lM<!% Hof/..6(aT^. 



Scale 1 ../..Q^GOO. Plotted Venfied 



Pioieclion :.'rr-.^. •./:.... "T-.^-fl 



Tn Sta ■.n.:L.:^....^S:& 



Topo Sta -.flt^! r.r-.. . /y.sC:3' 



Hvdfo Sta ■//■./r.:r...^.t(.:&- 



Datum /)/ort.h . RmerJcain . . /f*?5.7. 



Ret S,a . S/^ARF /9.^3, 



La. ^L..^3 /^M.T.f.^ Ad 



Long.../?'^ ^o 9^.7.:e 



Fici'RE 50. — Facsimile of Stamp No. 42, projection 

 and control data. 



