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Mooer Fe, ""TAE Marine REVIEW 29 have as much parallel middle body as possible. In the above series and in those given last year, this point has -- been kept in view. The three seriés, that with the fine bow, within the range of speed suitable for this form. At higher speed length ratios the somewhat easier form represented by 2B.2S seems to show up a little bet- ter than the one with the finer bow. The fuller and easier after body also seems better than the finer form. On | the same basis of curve of sectional areas in the above series, two more models were made, but of greater beam. ' The midship sections areshown on Plate 7; No. 2 had exactly the same curve of sectional areas as No. 1, the beam only changed. In No. 3 the same beam was taken as No. 2, but the area of the midship section was increased to compensate for the reduction dis- placement due to cutting away the form between sections 3 and 5 (Plate 1). Nos. 1 and 2 have therefore the same prismatic but different block co- efficients, while Nos: 2 and 3 have the same block but different prismatic co- efficients. The lines at the extreme ends in all cases are. the same. TABLE: OF - PARTICULARS. py B ic --_ -- ~- Mid- No. B d d Block. Prism. ship. F6. 1 8 2342 647.142 2.65337.5.67 78° .9638 62 7-272 © 2.142, 17.142 594. 6778 .874 Wo. 8 = 77272 2.140 17,142" .594 = 7664 .895 The curves of residuary resistance are shown in Plate 8 and the compara- tive results .in the following style: COMPARATIVE RESIDUARY RESIS- : : TANCES. Vv VL F6. 1 F6. 2 F6..3 8 100 96 96 i 85 100 95.4 92.3 9 100 92.3 81.2 Up to a speed-length ratio there is very little to choose between the three forms, but above that speed the effect of widening and fining the midship section is apparent by compar- ing curves land 2, By reducing the prismatic coefficient still further as in No. 3 there is a further reduction in residuary resistance. In fact the curve of sectional areas of No. 3 has all the good and none of the bad points of Nos. 1 and 2, the ends being fine and the lines toward the middle of a grad- ual character with no sudden change. In practice, especially where the mold system is used, it is of advan- tage from a builder's point of view to F'6. F7, and F8, represent a range of models of 0.6 to 0.85 block coefficients. -An investigation of the curves of re- siduary resistance shows that in the first place it is of decided advantage to use a parallel middle body and a fine. bow up to forms with about 0.8 block coefficient. Beyond that degree of fullness, the reverse is true, owing to the reasons discussed above.. There is no doubt that further im--- provements in performance may be ob- tained by fining the bilge diagonal, es- - pecially in the neighborhood where the parallel middle body joins the ends. In such cases, however, although there would be a virtual middle body, the actual middle body wouid more or less disappear. Further experiments upon this point are now under inves~- tigation. It may be of interest to note that in all the forms tested, where the ends were fine and accompanied by a- somewhat abrupt change to the paral- -- lel middle body, the -resistance "at very low speeds always appeared to be higher than in those where the ends were fuller and the forms more grad- ual. In any form there seem$ to be a certain' combination of fineness of water-line forward 'and curve of sec- tional areas which will give the best result. In other words, in the neigh- borhood of the water-line it is of ad- vantage to keep the form fine but. at some distance from the bow, there is Mooec. FS. pe eve ete cL en Fee ae ee -_--- Bene ie : ~~ * ee ee So 9 e WOLDNINeNe "e2 Saeed CREmOR mw of "08 -