224 ACTIVE TYPE OF STABILIZING GYRO. 



in my paper is for the purpose of completing this good work to the extent of the 

 entire prevention of rolling — instead of dealing with it in part it deals with it in 

 whole. 



With the new arrangement, the great longitudinal stability of the ship, which 

 is always present, can be laid hold upon and utilized athwartship to any extent 

 desired, not merely for the reduction and suppression but for the absolute preven- 

 tion of rolling, up to and including any wave increment or wave slope impinging 

 the ship. In fact the active gyro never operates in any other way; the ship never 

 responds to the wave slopes or any of the incessant wave actions; and never rolls 

 until the limit originally determined upon has been exceeded, and then the motion 

 amounts to only the small overplus or excess existing in some exceptional wave 

 increment which on the next half oscillation of the gyro is wiped out. 



It has been definitely ascertained, as has been well stated by a member of 

 our Council, Mr. F. L. DuBosque, in his kind words of discussion on this paper, 

 that at last we have in hand "the long-sought-for device that will prevent the 

 annoying rolling of ships." 



Dealing with primary resonance, Mr. Blohm's statement that "As soon as 

 it is proved that the ship always has the same or nearly the same period, the effec- 

 tiveness of the tanks would not be affected by the absence of the primary resonance 

 between waves and ship," seems to indicate that it is his belief that, so long as 

 the ship retains her period, the effectiveness of the tanks is unimpaired and remains 

 independent of the period of the sea with any given sea intensity. 



In answer to this I would call attention to Figs. 4 to 7, Plate 80, where the 

 tanks which were effective under the four quite widely differing conditions as 

 to intensity of sea when same was synchronous, have, as we see, become practically 

 useless ; nothing has changed except the period of the sea or the primary resonance 

 between waves and ship, and this only slightly. Here is a case taken from Frahm's 

 own work, fully corroborated by work on this side, which conforms to Mr. Blohm's 

 requirement that the ship shall retain its period, and yet the tanks have practically 

 gone out of business from no other cause than a slight change in the period of the sea. 



Mr. Blohm's statement that the period of a ship varies with change of load 

 from 3.73 to 4.61 indicates a change of approximately 30 per cent, about the same 

 as has been observed upon a tender ship rolling in still water and when steaming. 



I am glad Mr. Blohm mentioned the compound pendulum. All who are 

 familiar with this interesting mechanism know how entirely inoperative it is, unless 

 quite exact synchronism is maintained throughout the entire chain of pendulums. 

 Work with this compound pendulum is very instructive and serves to show most 

 emphatically how utterly circumscribed and limited is the usefulness of any device 

 tied down to a single period, especially in preventing motions of mixed periodic 

 origin. The pendulum always responds with perfect freedom to the first impulses; 

 later, often too late, the secondary pendulum or pendulums get under motion and 

 oppose to a certain extent further increment in the main pendulum, but by this 

 time the original impressed force has perhaps changed its period and the secondary 



