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March, 1913 The new non-resonance type of stabil- izer of Mr. Sperry's is always in per- fect tune with any impulse and is found to enjoy twice as many "breath- ing spells', as would seem apparent from the roll diagram, whereas a resonance device in the same sea _ will find between the decreasing and in- creasing portions of the record a lapse in phase between the sea and the ship, causing the pendulous mass to either |. DMN rahe THE MARINE REVIEW Messrs. Blohm & Voss, who are the owners of the Frahm damping tanks, upon the favor with which their in- stallations have been received. I look upon this effort to damp out part of the rolling of ships, even reducing it to 33 per cent, as Mr. Blohm states at one point in his discussion, as being in the right direction. I believe that our German contemporaries are doing excellent missionary work in educating wp ul MA TT Figure Noe O Gyroscopic Stabilization Figure NO Re es Same impressed forces 9S In figure no. 2l. | Steaming at 15 knots. give not enough or too much counter moment, often actually producing roll. Its low specific quenching capacity is, therefore, the very result of the reson- ance principle employed and due to the fact that only during an _ occasional --roll increment it develops moments that are in phase with and of the same magnitude as those received from the sea. Excellent Missionary Work Elmer A. Sperry:--Replying to the discussion by Rudolf Blohm, I wish to congratulate both Mr. Frahm and Figure No el Beg e Stilf Werer Down Record the public in the use of ships that roll much less than heretofore and to- ward ships that in the future will be entirely free from rolling. scale trials that have been prosecuted during the present year have ushered in a new era wherein ships will be entirely free from rolling. The tanks Mr. Blohm refers to, in his discussion are for the purpose of réducing the rolling, or suppressing it in part, whereas the active type of gyroscope described in my paper is for the purpose of completing this good work to the extent of the entire pre- vention 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 prevention of rolling, up to and in- cluding 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 The full ' 83 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, 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 effectiveness of the tanks would not be affected by the absence of the pri- mary 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 unimpared and remains inde- pendent of the period of the sea with any given sea intensity. -- In answer to this, I- would call at- tention to Figs. 4 to 7, where the tanks which were effective under the four quite widely differing conditions as to intensity of sea when same was syn- chronous, have, as we see, become prac- tically useless; nothing has changed ex- cept. 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 prac- tically gone out of business from no other cause than a slight change in the period of the sea. Mr. Blohm's statement that the perio 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. ie 2 J am glad Mr. Blohm mentioned the compound pendulum. All who are fam- iliar with this interesting mechanism know how entirely inoperative it is, unless quite exact synchronism is main- tained 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 use- fulness 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, farther increment in the main pendulum, but } :