TRIALS OF CRUISER KATHMAR II. 179 



of about 31^ degrees per roll at the beginning, in the middle about 2 degrees and about lyi 

 degrees along about the tenth roll. The friction coefficient shown by this curve is about 

 .35, or about five times that of an ordinary battleship, whereas the coefficient shown in the 

 model presented herewith is about 1/35, or .01. I call attention to these facts because they 

 have a significant bearing on the extinction and rolling. In the tank model the natural 

 friction of the model contributed very largely to the results, whereas in the gyroscopic 

 model the contribution is almost insignificant. 



"Referring to the four extinction curves shown under Fig. 24, we note that to the large 

 quenching increment in each case there should be added the quenching increment due to 

 the natural extinction. When these additions are made, reading from left to right, the full 

 alleged quenching increment becomes, respectively, 6.44, 3.99, 6.725 and 4.74, which it will 

 be noted in each case brings the total quenching increment above, and in most cases consid- 

 erably above, the wave increment. For instance, in the first to the left the quenching power 

 is somewhat over twice the wave power, in the second it is 25 per cent in excess, in the 

 third 43 per cent in excess, and in the fourth only slightly in excess. But in none of these 

 cun^es is the quenching good. In the second and third curves we would hardly call a ship 

 swinging through 10 to 12 degrees as being held against rolling, and in the last curve prac- 

 tically no quenching whatever is shown as the ship here is swinging through an arc of 44 

 degrees. Yet, I repeat, in each of these instances the quenching power is in excess of the 

 power of the wave received by the ship. 



"In this connection I wish to especially call attention to the fact that where the quench- 

 ing power is greatly in excess of the wave power, or where it is only to a small degree in 

 excess, or where the quenching power equals the wave power, roll quenching by the gyro 

 is practically complete in every instance ; in fact, the gyro stabilizer quenches all rolling 

 increments below and up to an equality with its powers so completely that the boat never 

 gets away and never starts rolling, and therefore no curves of this kind, where the stabil- 

 izing power is in excess of the wave power, are shown in connection with this paper because 

 operation under these conditions is too easy. 



"The interesting point is : what happens when the wave power is equal and in excess of 

 the roll quenching power of the gyros, and curves of this character only are shown in con- 

 nection with this paper. z\ll ratios below, as stated, are too easy and present no problem 

 that is of practical interest. It will thus be seen that this work is quite in contrast to the 

 widely published results with models supplied with damping tanks where the roll quenching 

 power was always in excess of the wave increments reaching the ship. 



"In curves 3 and 12 the gyro was used to roll the model. 



"On the lower line of each plate are given curves for different phase relations between 

 the ship and the sea, starting at the right with waves shorter and passing through syn- 

 chronism to waves that are longer than the natural period of the ship. Attention is called 

 to the fact that the wave increment in each case is in excess of the quenching increment, 

 this ratio being varied until the gyro fails in a measure to hold the ship, giving very 

 graphically what may be expected of the gyros under conditions where the ship is receiving 

 wave increments that are apparently considerably in excess of the powers of the gyro, in 

 fact, greater wave increments than the gyro stabilizer should be expected to handle and sup- 

 press. Connected with each of these curves is a portion where the gyros are cut out so that 

 the effect upon the ship of the sea running at the time is made instantly apparent. 



"The plant shown in Plate 115 was constructed for the Bureau of Construction and Re- 



