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488 dimensions of the model. Directly you begin to change displacement by adding middle body, on lengthening the model, you really alter all the conditions. The shape of sections also remaining the same, has elim- inated any chance of differences in results being obtained due to the shape of sections. In experimental work there is always a tendency to make too many changes at the same time, and the results therefore, are more or less vitiated. One cannot . tell exactly to what is due the change in resistance. One thing that must strike every- body in connection with the curves shown on Figs.6 and 7,1 think, is that never mind what the displacement of any particular model is, or the dis- placement length, that up to a certain parallel middle body, the residuary resistance is practically independent of the displacement; that is, it has practically the same value. When we pass a certain diameter of parallel middle body, however, the effect of increasing displacement, of increasing both length and breadth, is immedi- ately important. I would like to ask Mr. Taylor if some time in the future he would saw some of his models in half and try the effect of the combination of different ends. I have found, in ex- perimenting with certain models, that the easier form of after-body drives with rather less resistance than the rather fine form, and I think possibly the minimum resistance would be re- duced if Mr. Taylor took his best bow and tried some of the other forms with slightly less middle body and the fuller form immediately aft. Mr. Thomas M. Cornbrooks. Thomas M. municated.) Cornbrooks. (Com- I am very much inter- ested in this article by Mr. Taylor, as it is of great value to those of us who are anxiously' wrestling with problems of this sort, which are in- » timately associated with both the cost of building and in running steamers of this type. We are very fortunate in having the results of model tank experi- ments of two ships which fall within the range of this paper. As the re- sults fall very close to the curves given on Figs. 7 and 10, I append herewith a data of these trials. Ship No. 1 is 488 ft. between perpendicu- Jars, 58 ft. beam, and was tried at two draughts, data for which I shall give as A and B. THE Marine REVIEW A--12 knots speed. Percentage of mid- Ship = bOdys ee rece e see a see see ee 42 Es Fi. P. 1630 V VL St F. H, P. 1410 R. HP. 220 D (L) 100 98.2 OD, 7s Midship section coefficient.... .97 Rr, lbs. per ton displacement .52 Displacement 5. ose sce. 3 v's 11410 B--12 knots speed. Percentage of mid- Slap. WOGV) (oyu eee ha ce ces colnet ey esis 42 E. H.. P. 1882 Vv VL 1 2D F. H. P. 1407 R. H. Ps 475 D (L) (100) 145.3 BG: .80 Midship section coefficient.... -80 Rr. lbs. per ton displacement 76 Displacements: oe. he rcs eos 16892 No. 2 ship is 385 ¢t. between per- pendiculars,. 53 ft. beam, and was tried at load draught only. 12 knots speed. Percentage of midship SOCOM ie deen ee ie snes Saiste na ch eer ase ae He He PR. .1780 NE ib 61 F. H. P. 1050 : R. H. P. 730 D (L) (100) 196 LC, .80 Midship section coefficient... -569 Rr. Ibs. per ton displacement 1.76 sieiere see erene eae 11200 Displacement Chairman Taylor: Does Mr. Tay- lor wish to add anything to the dis- cussion this morning? December, 1909 D. W.. Taylor:..I will. say with reference to Prof. Hovgaard's re- marks; that I should be glad to add to the paper when permanently print- ed the additional curve of residuary resistance of the models with the 0.68 and 0.80 longitudinal coefficient. My only object in leaving that out was to reduce to some extent the size of the paper. If it is of interest to the members, I shall be glad to add them. We have made no experiments with varying models, having identical ends and varying length of parallel middle body. I think that Mr. Froude's classical paper on the subject leaves very little to be covered by the gen- eral features which would be found, and that is not a problem of serious practical interest, as a rule, because you seldom can vary the length of the ship very much, when it comes to. be designed. I will have to take Prof. Hovgaard -aside and explain how these derived forms are obtained. I tried to make the matter plain, but if I did not, I will take him aside and explain it. In regard to Prof. Sadler's remarks, we have madea number of experiments with various ends of models, having the same parallel middle body. We built models with separate ends, and bolted them together, and as long as the midship sections were the same, we could combine any bow with any stern. We have done none of that with the parallel middle body model. The Influence of the Position of the Midship Section Upon the Resistance of Some Forms of Vessels. ROE. HH, Co Sadler: then: read! his paper entitled "The Influence of the Position of the Midship Section upon the Resistance of Some Forms of Vessels." The paper follows: The following experiments rep- resent a short investigation of the influence of the position of the "midship section" upon resistance, this term being used to designate the section of. maximum. area. The two sets of models tried were of ordinary form, and in each series the length, breadth, draught, displacement, sections and curve of sectional areas were kept constant, the only variation in the form being that due to ex- panding or contracting the forr ward and after body due to plac- ing 'the midship section at va- rious positions in the length. When the midship section is at the center of the length, the curves of sectional areas in both models were the same for both forward and after bodies. Al- though this form of curve of sec- tional areas is not necessarily the best, - it was adopted in this par- ticular series on account of some other investigations. PARTICULARS OF MODELS. TABLE 2. L408 Ee Coefficients.-- Mod 'B ra ra Block. Prism. Mid. sect. A. 8 2.143 17,14. 0.503 0,538 0.935 B- 8 2.143 17.14 0.567 0.606 0.936 Model A has a rather low pris- matic coefficient for a vessel of ordinary form, but this again was chosen in view of future experi- ments. The curves of sectional areas for the two models are shown in Fig. 1. In each case the midship section was placed in four posi- tions: (1) at the center of the length; (2) at 5 per cent of the length aft of the center; (3) at 10 per cent aft, and (4) at 10 per cent forward of the center. The curve for séctional areas for (2) is omitted and that for (4) is not 9 shown as it is simply (3) reversed. The curves of residuary resist- ahr i