220 ACTIVE TYPE OF STABILIZING GYRO. 



As to Mr. Sperry's words on page 201 that " it is sufficient to say that experience 

 has demonstrated that damping tanks are disadvantageous, if not positively 

 dangerous, when out of synchronism," I want to say that it is a special feature 

 of the new devices of anti-rolling tanks that they are fitted with an air pipe, con- 

 necting the tanks on both sides of the ship, and that this pipe has a valve which 

 may be closed. In this case there will be no free water surface, as in the earlier 

 anti-rolling devices of Sir Philip Watts, Professor Biles and others, where the water 

 was allowed to rush through from one side of the ship to the other. In the Frahm 

 tanks the movement of the water can at any moment be controlled by blocking 

 the air connections and, by throttling the air, the oscillations of the water may be 

 adjusted to the conditions of the sea. So there is positively no danger connected 

 with the water in the tanks. I think the best proof concerning the reliability of 

 anti-rolling tanks is the fact that the Hamburg- American line has already installed, 

 or is installing, the Frahm tanks into all of its big ships, including the Imperator 

 and her two sister ships of 55,000 tons each, and nearly all other important German 

 lines running passenger steamers are doing the same. 



The Cunard line also is installing the tanks into its latest and biggest ship, 

 the Aquitania, after having given them a thorough trial in the Laconia, com- 

 missioned last year. In fact, the sum of the displacements of ships in service or 

 under construction, fitted with Frahm anti-rolling tanks, now amounts to 551,200 

 tons. I do not think that the responsible men of all these companies would take 

 the risk of installing the tanks, if there were any danger connected with them. 



Mr. Maxwell W. Day, Associate (Communicated) : — In paragraph (c) on 

 page 198, Mr. Sperry has stated that the use of the gyroscope saves power in pro- 

 pelling the vessel on account of the elimination of rolUng. It would be interesting 

 to know how much less power is required to propel a vessel in rough water when 

 it is maintained steady by the gyroscope than when allowed to roll freely. 



Also, he mentions the longer period of the roll of the vessel when steaming 

 as compared to the period when not under way. It would be interesting to know 

 how much longer this period is and what is the reason for it. 



Mr. Carl It. NordEN, M. E., M. S. M. E. (Communicated): — I have read 

 with great interest Mr. Sperry's paper on a subject to which I have given much 

 time. I have also read the discussion of Mr. Rudolf Blohm. I beg to add a few 

 words regarding the new stabilizer and its quite remarkable performance. 



First, with regard to Mr. Blohm's conclusion "that any anti-rolling must 

 be designed for the case of resonance." This may be based on the assumption 

 that such a device is only required to reduce excessive rolling, which, as we all 

 know, happens when a vessel receives a series of strong impulses somewhat in 

 phase with its own natural period. Mr. Sperry's conception of true stabiUzation 

 is an entirely different one. With Sir Thornycroft, he believes, on the contrary, 

 that a stabilizer should exert upon the ship, at all times and up to its rated capacity, 



