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is our experience that as a rule they run slightly better by the stern and slightly worse by the head. The difference is slight, and may be en- tirely utilized in many cases by a change in difference of form of model, but taking a broad average they seem to run slightly better by the stern than by the head, and that was also very strongly the opinion of a ma- jority of seagoing people. They pre- fer to have the ship trimmed by the stern, and they say that the vessel will go through the water better. I think, however, that many seagoing people exaggerate that. There is one thing--looking at Figs. 2 and 3, the last figures, it is seen that there is a distinct minimum of resistance for a number of the curves --as pointed out by Prof. Sadler, when the midship. section is between the central position and five per cent aft, but you will see that the strong minima, referred to the curves of the speed length of coefficient, of 1.0 above, and for the speed coefficient from 0.9 down. The difference of the variation in resistance, when the midship section: is as much as 9 per cent aft, is really very small, and after all, I presume that 95 per cent of the ships built have a speed length ratio of less than 0.9, and that is somewhat encouraging, as it encourages us to. believe that we may vary the position of. the mid-_ ship section somewhat, from the posi- tion of center of buoyancy if desir- able, in consideration of freedom from errors, without any serious pre- judicial effect' on resistance, and I think this a very desirable thing to know. © Effect of Raking Midship Section. Ee' As. Stevens: «I. ask if the ef: fect of raking the midship section has been investigated? It has a bear- ing, to a certain extent, in the case of torpedo boat models, etc., which seems to require that the greatest width of the water line should be aft of the position occupied by the lower lines. That form of vessel is gotten up more especially fon high speeds, particularly higher speed ratios. Prof. Sadler: I would like to con- firm what Mr. Taylor has said in re- gard to the general tendency of ves- sels when they are trimmed by the stern or by the bow, in connection with resistance. We have found the same thing that usually most vessels drive a little easier when trimmed by the stern. In the case of some of the very full types, however, the re- verse seems to be true, with certain models. I have found some with TRe Marine Review Model. B. December, 1909 very full ends that seemed to drive a little easier when trimmed by the bow. With regard to raking the midship section, personally I have not tried Forward Position of M idship. Section Fic. a any experiments .on that up to the present. We hope to do so at some time in the future. I would not like to say off-hand what the result of that would be on different types. Some Ship-Shaped Stream Forms. HE fourth paper was upon the sub- "ject "Some Ship-Shaped ,Stream Forms," by William McEntee, assist- ant naval instructor, being the results of an investigation made at the ex- perimental model basin in Washing- ton while the author was on duty there. The investigation had for its principal object the determination of the variation of velocity of water when constrained to move in a' plane along a form of the shape of a ship's waterline or more properly,.' 'water plane. The main conclusions from the investigation are: First, that hol- low waterlines cause less wave-mak- ing disturbance than straight or con- vex waterlines and that, as the hol- lowness and fineness of waterlines are increased 'the wave-making disturb- ance decreases to a minimum after which, if the lines are made still finer and hollower, the wave-making dis- turbance again increases. Discussion on McEntee's Paper. Capt. William Hovgaard: Mr. Mc- Entee states on page one two main conclusions, and the last of these is that "as the hollowness and fineness "formula of water lines are increased, the wave making disturbance decreases to a minimum, after which, if the lines are . made still finer and hollower, the wave making disturbance again in- creases." That conclusion corresponds very well with an analysis which I have made of a. great number of water lines, and of the resistances of a great number of ships, and these analyses were published in the trans- actions of tthe British Institution of Naval Achitects .Jast:. year,:<.In ex- amining the obliquity of a great num- ber of water lines on actual ships, I find that the obliquity could be repre- sented by a formula. . (Constructs on the blackboard.) .You will find first in the very full lines the obliquity is very light, and then it decreases, and there will be a mini- mum, after which it: will again. in- crease with the very fine lines, so that the obliquity becomes a form equally present, and becomes a para- bola. This is the value for which the obliquity is a minimum. (Indicating on blackboard.) That value is found to be about 0.55. I also analyzed the residuary resistance of a great num» ber of ships, and found that it could BE Nat pe ER 9 i Hae ee ed ae ie ea el ae