390 



REPORT 1892. 



' Probably the most ordinary application of graphic representation in 

 this connection is the "curve of displacement," in which the ordinatesare 

 drafts in feet, and the abscissse are tons. For merchant vessels this curve 

 is usually of the character shown in the accompanying sketch, fig. 13, the 

 upper part of the curve approximating very closely to a straight line. 



' Another curve much used is a curve of " tons per inch of immersion," 

 in which the vertical scale is again a scale of drafts, and the horizontal 

 scale a scale of tons per inch. 



' Its character is generally somewhat like fig. 14. It is used in calcula- 

 tions of trim, and to estimate small variations of draft in terms of tons, or 

 vice versa. 



' Another curve of considerable service is a " curve of midship section 

 areas," in which, again, the vertical scale is a scale of drafts, and the 



Fig. 14.— Tons per Inch of 

 Immersion. 



Fig. 16.— Curve of Block Coefficient. 



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horizontal scale, a scale of superficial feet. Its general character is very 

 similar to that of the curve of displacement. The use of the curve is to 

 estimate the area of the furrow, so to speak, ploughed in the water by the 

 ship's forward progress. 



' Another curve which is sometimes plotted is the curve of "block co- 

 eflBcients," or the ratio which the volume of the immersed part of a vessel 

 bears to the volume of a parallelopipedon of the same extreme dimen- 

 sions, and is useful for comparison of ship with ship. 



' Its vertical scale is a scale of drafts, and its horizontal scale, a scale 

 of decimal parts, or percentages. Its general character is much like that 

 of the curve of tons per inch of immersion (see fig. 15). 



' Somewhat different kinds of curves are the curves of " locus of meta- 

 centres " and of " locus of centres of buoyancy " (tig. 16). As these points 

 are heights on the same vertical, varying with the draft of the vessel, 

 which may also itself be considered as a height, all the points representing 

 difl'erent conditions would range in the same straight line, and would thei-e- 

 fore be confused. To meet this difficulty two scales of draft are drawn, at 

 righb angles to one another, and the points in the curves are marked 



