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HYDROGRAPHIC MANUAL 



83) shall be shown nearby with arrows 

 pointing to the area on the original scale 

 plot. Such plans need not contain a scale or 

 be surrounded by a margin. Each plan shall 

 show in figures the principal dimensions of 

 the pier. 



6-7 Smooth sheet layout and scales. — 



The smooth sheet will generally duplicate the 

 boat sheet in area coverage, orientation, and 

 size. It is sometimes constructed concur- 

 rently or the boat sheet may also be the 

 smooth sheet (see 1-10 and 6-45). At times 

 it is advisable to modify the original sheet 

 layout when unforeseen factors are intro- 

 duced during field operations. Most of these 

 factors are discussed in 6-4, 5 and 6. 



The scale of the smooth sheet will gen- 

 erally be the same as that of the boat sheet, 

 but in some cases it is desirable to use a 

 smaller scale in order to reduce an oversize 

 boat sheet, to eliminate an undesirable 

 skewed projection, or to combine two adja- 

 cent surveys. Authority to plot a survey at 

 a reduced scale must be obtained from the 

 Director (see 2-19). Such reductions will 

 be authorized: (a) when the smaller scale 

 will not significantly detract from the value 

 of the survey ; (b) where charts at a larger 

 scale are not contemplated ; and (c) where 

 the hydrography has revealed no shoals or 

 submarine features which cannot be ade- 

 quately shown at the reduced scale or on 

 subplans or overlays. 



Large scale smooth plotting is generally 

 confined to subplans described in 6-6. 



6-8 Preparation and protection. — The 



smooth sheet shall be allowed to cure or be- 

 come conditioned to its plotting environ- 

 ment for as long a period as is practicable 

 before the projection is drawn. Each sheet 

 should be laid out or hung up separately 

 where it will be completely exposed to the 

 air on both sides for at least a few days 

 before use. For best results the period of 

 seasoning should embrace a wide variation 

 of temperature and humidity. If the sheet 

 cannot be seasoned by laying it flat, it should 

 be suspended from successive edges and sub- 

 sequently laid flat for several days. It shall 



be kept flat at least until completion of the 

 projection and, if applicable, the checking 

 of concentric control circles. The sheet may 

 then be rolled loosely, if necessary. How- 

 ever, it is best to keep the sheet flat until all 

 plotting is completed. When it is not being 

 used, the sheet should be covered by a suit- 

 able protective canvas or other table cover. 



The sheet shall be protected at all times 

 from creasing, defacing, or smudging. All 

 parts of the sheet should be kept covered 

 except the small area on which work is ac- 

 tually being done. It is equally important 

 to avoid indentations made by using sharp 

 pointed or chisel-edged hard pencils. Tem- 

 porary notes should be made lightly with a 

 3H pencil so that they may be erased with- 

 out damage to the paper. 



6-9 Check of drafting instruments. — The 



drafting instruments used in smooth plot- 

 ting are subject to imperfections and should 

 be tested before and during use (see 3-18, 

 21, 137 to 140). Some may be corrected by 

 adjustment, others by applying calibration 

 corrections, and others only by repair. Im- 

 perfect or unadjusted instruments may re- 

 sult in serious inaccuracies in the smooth 

 plot. Particular attention is required to 

 check plastic protractors as they may warp 

 while in use. 



6-10 Projection. — Procedures for con- 

 struction of a projection are described in 

 Sections 1-12 and 5-6, 7, and in Special Pub- 

 lication No. 5. The smooth sheet projection 

 should be constructed with more care than 

 is required for a boat sheet. 



6-11 Circle lines of control. — Concentric 

 circles or segments of circles representing 

 distances or corresponding time intervals 

 used in plotting electronically controlled hy- 

 drography shall be drawn soon after the 

 projection has been completed in order to 

 avoid distortion problems. The technique of 

 positioning and drawing the circles is de- 

 scribed in Sections 5-11 and 12, and in Coast 

 and Geodetic Survey Journal No. 3, 1950. 

 Each series of circles shall be identified by 

 a distinctive color. Contrasting colors should 

 be used, however yellow and orange colors 



