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362 THE Marine REVIEW September, 1910 A GRAPHICAL METHOD OF POWERING SIPS Swney Graves Koon, M. M. E. VERY new ship is tons, and K is the Admiralty co-efficient. read off, almost at a glance. The prep- the subject of a It is in the choice of this co-efficient aration of the curves requires the cal- computation to de- that the judgment of the designer makes culation of a number of separate cases, termine the horse- itself most apparent. The figure will be but, once calculated and carefully plot- power requisite to higher with fine models than with fuller ted, a great saving of time enters into drive her at the de- ones; higher with moderate than with the determination of the horsepower for sired speed. These higher (relative) speeds; and very the next proposed ship. A single set of calculations are made slightly higher with large ships than curves, based on a single assumed value in various ways, but the great majority with smaller ones of the same form. Of K, would obviously not fit aes are based on the so-called Admiralty There is no available substitute for but our equation shows us that this co- D* V3 the judgment of the designer; but, in efficient enters as a direct factor; hence, formula, H=--------, where H is the cases where large numbers of designs if Our curves. are ee oF a_ basis K are under consideration, it is quite pos- Of K:, and our designer's judgment horsepower required for speed V in sible to construct curves from which Places the value for any given ship at i i i i i i K., then the result obtained from the hip's displacement in the desired result in horsepower may be 2 a Se eee : curves, multiplied by Ki and divided by K., will produce the required horse- ee ' ? r ] -- power. | i Suppose we desire the horsepower re- | / / / quired to drive a ship of 13,000 tons T f a a - displacement at a speed of 20 knots. The Admiralty co-efficient is placed at (say) 240. Then D%*= (13,000)* = Sod) ve = 0 = 8000; H = 553 X 8,000 ---- == 18.433. If, now, we di- 240 Be vide H by D, we obtain 1.418 as the units of horsepower per ton of dis- placement. By continuing in this manner, we may readily obtain enough information about the powers required to drive such a ship at various speeds, to be able to plot a curve in which values of H/D ap- pear as ordinates, based on values of V as abscissae; and similarly for other displacements. Such curves, for dis- placements varying from 1,000 to 27,000 tons, all based on K = 240, are shown in Fig. 1. The dotted -curves shown are included more as a matter of aca- LSS demic interest than of practical value. Zs CA Each dotted curve carries a definite Fy 1) ioe i = -- So ) -- ! ap a D bos _ ee me - SS PS pH Ra Sc Poss S eS eo ~ Pa ee ba od -- oe a pe os -- <-- es NN 3, Ns DISPLACEMENT iN THOUSANDS OF TONS ! , r | / se Ce HK! AL f or value of H/D, such as 1.5, through suc- - f ; pa cessive values of V corresponding to | E ne Vas | ele variations in D. / 4 Le AAC Fig. 2 shows another method of plot- ni ie A A : : . ° . ] 7 ey ee yr ting the same information as is given 7) ed 7 eo A 5 by the solid curves of Fig. 1. Here the oe g LV oe ve ES a 7 value of H/D is again the ordinate, but oe ee a | vs | the abscissa is D, while each curve rep- oe . ELLE | oP ; _ Yresents a definite and constant value ¥ if. | . a LEG 4 a | of V, all with K = 240, as before. In a | 7. os | | some respects this is more convenient o ot oe | for reference than is Fig, 1. | | 10 ; 13 16 19 22 25 EXAMPLES. SPEED IN KNOTS tp = 16,000 ; V _-- 21: ke -- 225: Fic. 1. MW? On Higol, the curve for D =