178 MODEL EXPERIMENTS AND SPEED 



DISCUSSION. 



The Chairman : — This paper, No. 16, "Model Experiments and Speed Trials of the 

 60-Foot Motor Cruiser Kathmar II," is now open for discussion. No doubt there are a 

 number of our members who are interested in this question of trials, model experiments, 

 and that class of experiences, and as the paper undoubtedly contains valuable information, 

 I think that some one might, perhaps, care to say a word in discussion of the paper. If 

 there is no discussion, we will extend the thanks of the Society to Mr. Luders for his paper. 



The next paper is No. 17, entitled, "Some Graphic Studies of the Active Gyro Stabil- 

 izer," by Mr. Elmer A. Sperry. 



Mr. Sperry, in presenting the paper, said : — 



"I desire to make just a brief reference to the work that has recently been done the 

 world over on the study of rolling. The work of Frahm, supplementing as he did the orig- 

 inal work of Sir Philip Watts, opened up anew these experiments. Coming from Italy, 

 from the hand of the great Commodore Russo, there was a very valuable contribution to 

 our knowledge of the rolling of ships, especially in the effort to dampen such rolling by the 

 use of tanks. This work was about simultaneous with a very able paper by Sir Philip Watts, 

 read before the British Institution a year ago, and which in turn led Sir Philip and Profes- 

 sor Biles, another original worker in this line, to encourage further experimentation in 

 England, and as a result two important papers were read before the institution this year. 

 That by Professor Woollard was especially gratifying in checking up the results obtained by 

 Commodore Russo, and also in developing the fact that tanks at certain points in the phase 

 relation between ships and waves are positively dangerous. 



"Professor Woollard's paper. Fig. 2, referred to in the last part of my paper, which 

 illustrates the damping power of tanks for different phase relations between the ship and the 

 sea, very graphically illustrates the well-established fact that tanks have their greatest stabil- 

 izing power when the sea is synchronous with the period of the ship, and that there is a 

 region each side of this region of synchronism, and quite close to it, where the power of the 

 tanks falls to very low values, then rises a little both to the left and to the right, but at- 

 taining in neither of these regions more than a small fraction of its power at the point of 

 synchronism. In the present experiments I have been careful to explore this same region, 

 starting away below synchronism and passing through synchronism to points considerably be- 

 yond, with the results given in Plates 113 and 114. 



"In this connection it is interesting to note that whereas the usefulness of the damping 

 tanks seemed to depend almost entirely upon the phase relation between the period of the 

 ship and the period of the sea, with the gyroscopic stabilizer its usefulness seemed to be en- 

 tirely independent of any phase relation and its demonstrated efficiency in sea trials seemed 

 to be well above 90 per cent, and in instances above 95 per cent, for all phase relations 

 and under practically all conditions. 



"With reference to the two large plates showing the curves, I wish to call your attention 

 to the quite marked difiference in frictional resistance between the cycloid model used in the 

 present work and that of the model used in the most widely published experimental data we 

 have in reference to tanks. In Fig. 24, Plate 113, some of the curves in reference to 

 tanks have been reproduced. The extinction curve of the tank model is shown at the extreme 

 right, Fig. 24, whereas a small extinction curve of the gyroscopic model is shown at the ex- 

 treme left in Fig. 1, Plate 113. By examining this cun^e we see that there is a reduction 



