Maritime History of the Great Lakes

Marine Review (Cleveland, OH), July 1909, p. 197

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July, 1909 our ships meeting there is an inclination to come together. When a ship is overtaking another in a nar- are row channel there is a tendency for. the faster ship to carry the slower one with her. They will see-saw for miles. 'When the passing ship gets her stern by the boiler house of the other ship there seems to be a.tendency for the overtaken ship to fall in towards the overtaking ship. When the ships are alongside the vessels are both very sensitive in the matter of steering. Masters are reluctant to check or back--everthing seems to act by con- Similar conditions do not al- traries. ways produce similar results, how- ever. Relative. speed and_ relative size are influential factors. Suction is severe when a_ deep draught ship overtakes a smaller ship though sometimes the smaller ship will sheer the larger. We call it the mysterious force of suction. We might ask this . society to evolve a rule which might guide us in this particular. It is one of the things that we would, like to find out. The practical way we meet it now is not to pass in the same di- rection unless there is ample room and ample water. "Prof. H. C. Sadler.--I would sug- gest that naval constructor Taylor be invited to reply to this discussion. The question of suction is a vital one to us on the lakes. At Ann Arbor we have made a few experiments in shallow water by putting in a false bottom. The behavior of the model has been erratic. The flow of water at the stern is disturbed and drawn in at the sides. The propeller effect is greater on the lakes than Mr. Tay- lor imagines. Mr. Goulder's remarks seem to establish the fact that suction is a very real thing. I think a series of experiments should- be carried on in shallow water. Capt.. George A. -White.--And _ re- member that side-wheelers have suc- tion also. "A Method of Determining Pressure for Steam Turbines." Mr, J. J. Crain then summarized Prof. C. H. Peabody's paper entitled "A Method of Determin'ng Pressure for Steam Turbines," as follows: The usual methods of designing steam turbines are based on adiabatic computations modified by factors to take account of the effect of steam friction. As applied to a _ simple Steam turbine the method appears to be fairly satisfactory, provided that the friction factors can be properly assigned. But when applied to tur- 'THE Marine REVIEW bines which have two or more pres- sure stages, a complication comes from the fact that the heat which is due to steam friction remains in the steam and increases the entropy. The influence of this effect is understood by turbine designers and allowance is made for it one way or another. Writers on steam turbines usually ig--- nore the effect or touch on it lightly. This paper gives a method that can be used with the aid of the author's Steam and Entropy Tables to deter- mine directly the pressures of a com- pound steam turbine, taking into ac- count the increase of entropy due to steam friction. The influence of increase of entropy and the method of allowing for it are illustrated by a simple computation for a turbine with two pressure stages, such as has been used for the Curtis turbine. In order to show the degree of precision to be expected this compu- tation has been carried cut with the precision that the table affords, and cross-interpolation is resorted to when necessary. It will be found that near- ly, if not quite, as concordant results © will be had if the temperatures are selected to the nearest half degree and \if the nearest entropy column is taken without interpolation. In fact, for practical work it will generally be sufficient to use the entropy table without interpolation, using the near- est temperature and the nearest en- tropy column. The author observes that to show that this method (or any equivalent method) is valuable for turbine de- sign, comparison with experiments is desired. The experimental results are mostly in the hands of turbine build- ers and "much reticence is observed regarding their publication." "Resistance of Some Full Types of Vessels." There being no discussion upon Prot. Peabody's paper the meeting proceeded to consider Prof. H. C. Sadler's paper upon "The Resistance of Some Full Types of Vessels." The paper follows: In the region of the Great Lakes, perhaps more than anywhere else, the very full type of cargo vessel pre- dominates; and, as the meetings of the Society are to be held in Detroit this summer, the 'results of some ex- periments upon the resistance of ves- sels of full form may be of interest. It may be thought that vessels hav- ing a block coefficient of from 0.80 to 0,86 and a prismatic coefficient of 197 from 0.83 to 0.89 do not offer much Opportunity for .appreciable variation of form under given conditions as to dimensions. It may also be questioned if such changes as are possible will produce a marked effect upon the resistance or indicated horsepower, be- cause, at the speeds common in ves- sels of this type, the surface friction represents the principal part of the resistance. The problem in a somewhat dif- ferent form is constantly arising in practice, and is generally one where additional carrying capacity is required upon limited dimensions without ap- , preciable addition to the horsepower, the. speed. remaining constant. _ Although -the subject: has not been investigated to its fullest. extent, the results - given 'below show the. pos- sibilities. of improvement in the form of vessels of this type, and also give a certain amount of data which may be useful. Figures 1 and la show 'the curves of sectional areas and the body plan of a wide and shallow type with the following coefficients: L REE SRE GS 4.35 4.35 4.35 B B ee oe Bie 6.17 4625 337 d Block coefficient ..... 0.822 0.845 0.858 Prismatic coefficient... 0.839 0.858 0.070 Midship. section coeffi- . CLONE Oe ER ees 0.98 0.985 0.986 The .model was tried at three draughts and the curves of residuary resistance per ton. of displacement are shown im Pig, 2 . _ At the deepest draught the counter was partially immersed in still water, _but as this also happened at the lesser draughts when the model attained moderate speeds, the conditions are practically similar. Time did not permit any modifica- tions in this form, which, as will be seen, is of a ship-shape character; but, in all probability, as good if not better results might have been. ob- tained by adopting a more typical "scow' form,' especially at the speeds usual: for this type. The body plans and sectional area curves of the next series to which attention is called are shown on Figs. 3. and. 3a: In, this... setied. . certain modifications -of form were made which consisted mainly in fining the lower part of the sections at some distance from the bow and also easing the form where the fore body joined the parallel midship body... The dis- placement, therefore, varies for each modification as shown in the. follow- ing table: ve

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