6. THE SMOOTH SHEET 



223 



and periods must not be used. The abbrevi- 

 ations shall be lettered in single stroke slant- 

 ing letters with the capital letters not more 

 than 2 mm in height. 



Bottom characteristics should be placed on 

 the smooth sheet reasonably close to and a 

 little below and to the right of the soundings 

 which they accompany, provided there is 

 adequate space. Otherwise the -characteris- 

 tic can be placed in any convenient place 

 nearby. However, in displacing the charac- 

 teristic it shall never be placed where it does 

 not represent the nature of the bottom un- 

 less displacement is indicated by a penciled 

 arrow. The descriptive note "Rk" should 

 always adjoin least depths on submerged 

 rocks when so identified in the sounding 

 records. 



6-63 Standard depth curves. — After all 

 the soundings are plotted standard depth 

 curves listed in Table 3 shall be lightly pen- 

 ciled on the smooth sheet. The curves will be 

 inked in the specified colors after office verifi- 

 cation (Fig. 82, 83). Depth curves, or curves 

 of equal depth, are comparable to contours on 

 land and the principles governing the deline- 

 ation of contours are equally applicable to 

 the drawing of depth curves. 



The curves shall be drawn with a 3H pen- 

 cil having a slightly rounded point, never 

 a sharp one, and care shall be taken not to 

 indent the paper. Inked lines shall be less 

 than 0.4 mm wide, and in congested areas 

 should be consistently about half this width. 



Depth curves shall generally be drawn to 

 include soundings of equal depth or less, but 

 they may be broken at soundings in order to 

 avoid unnatural bottom configuration. Curves 

 shall never be broken vertically above and 

 below the numeral 1 or on a 45° align- 

 ment with the left part of the numeral 4. 

 They should never overlap or cross a letter, 

 numeral, or symbol. Curves should be broken 

 into long dashes where they are not ade- 

 quately defined. In some inshore areas only 

 short sections or indications of curves can 

 be drawn. Where they can be extended 

 with reasonable certainty of position, in- 

 shore depth curves should be completed to 

 the extent determined by the hydrography. 



In comparatively shoal depths where there 

 may be dangers to navigation, one should 

 always err on the side of safety in drawing 

 depth curves. 



The curves shall not be drawn mechani- 

 cally ; they should delineate a natural bottom 

 configuration, but from a cartographic view- 

 point the minor irregularities in soundings 

 should not be over-emphasized in drawing 

 the curves. There are two reasons for this 

 policy; first, with soundings plotted in inte- 

 gers a tenth of a unit change, 0.7 to 0.8, re- 

 sults in a full unit change in the plotted 

 sounding; and second, continuous minor un- 

 dulations and irregularities along a depth 

 curve lessen desired emphasis on the more 

 significant irregularities. These criteria are 

 difficult to detail in a description and are 

 best cited by illustration (Fig. 85). Generali- 

 zation is desired to a point, but significant 

 configurations of the bottom shall not be 

 masked by un judicious smoothing of curves. 



The use of i/^-^oot fractions for judicious 

 modification of curves is specified in 6-55d. 

 This V-j-foot leeway also applies to 0.1 fathom. 

 Either should be omitted to eliminate un- 

 natural curve delineations and to smooth in- 

 significant irregularities. Both should be 

 omitted for emphasis of the apex of a shoal 

 or end of a spur or elongated shoal. The frac- 

 tion should be plotted where it will eliminate 

 nearby detached curves over smooth bottom 

 and where definite continuity of deeper water 

 should not be interrupted by a closed curve, 

 particularly in channels. 



When drawing the depth curves, constant 

 reference should be made to the boat sheet 

 where the bottom configuration is already 

 outlined. Although boat-sheet delineations 

 will not necessarily be duplicated on the 

 smooth sheet they do serve as an excellent 

 and generally authoritative guide. 



6-64 Selection of curves. — Supplemental 

 curves specified in Table 4 should be added 

 in shallow waters where there is consider- 

 able distance between standard curves or 

 where the supplemental curves provide bet- 

 ter definition of submarine features. They 

 should also be used to delineate significant 

 features such as least depths, tops of shoals. 



