OF GYRO-STABILIZER FOR SHIPS. 49 



by Mr. Sperry, I want to put a specially interesting test before you gentlemen which we made 

 in this respect. We had experience with two sister ships, one with bilge keels and the other 

 with rolling tanks and without bilge keels. There was an appreciable difference in favor of the 

 latter, as far as I can remember about .43 knot at 29 knots. 



I think that is very great proof of the value of an invention like Mr. Frahm's or Mr. 

 Sperry's in the direction of the development of speed for the faster ships which are to come 

 in the future. 



The President: — Are there any further remarks? Mr. Sperry, do you want to reply 

 to the comments that have been made? 



Mr. Sperry : — Replying to Mr. Orbanowski, there is no limit to the size of ships 

 to which the stabilizer can be applied. The weight goes down, comparatively, as the size 

 of the ship increases, as mentioned in the paper. We find that smaller boats require more 

 stabilization, relatively, as is apparent, because a given wave interferes with a small boat to 

 a greater extent that the same wave interferes with a large boat. The stabilizing unit se- 

 lected for the 10,000-ton naval vessel I mentioned weighs 80 tons, including entire equip- 

 ment and all auxiliaries. That is .8 of 1 per cent of the displacement. That plant will abso- 

 lutely hold the ship against all beginnings of roll up to nearly 4 degrees for any single wave 

 increment arriving from either side. For larger ships the plant should never, I would say, 

 go above 1 per cent of the displacement. The entire plant is small as compared with the ship; 

 you can hardly find it on board. 



One word, now, as to anti-rolling tanks which were referred to by Mr. Orbanowski. 

 These are in line with practically all attempts at stabilization prior to the work on the Worden ; 

 that is, the stabilizating moments in each instance depend for their very existence upon 

 a certain amount of motion being first acquired or developed by the ship. When these mo- 

 ments are finally generated they act to reduce the roll so as to cut it down by some predeter- 

 mined fraction only. 



With anti-rolling tanks it was found that a certain critical condition existed between 

 the natural period of the waves of the sea, the natural period of the ship and the period of 

 the water in the tank which, when brought into proper adjustment, would bring about a min- 

 imum of motion of the central element, namely, the ship, and the maximum activity of the 

 water pendulum. But it was found, upon trial, that this relation was not only critical to the 

 point of being theoretical, but very difficult to attain and still more difficult to maintain, the 

 wave period being non-persistent and very erratic. 



The Construction Bureau of the British Admiralty after critical trials reported that the 

 stabilization depending upon this relation, which was the only stabilization from tanks worth 

 mentioning, could only be secured about once a year when the three relations happened to 

 come right. What happens, however, when these conditions are wrong, as they nearly always 

 are, is that the tanks then increase the roll instead of decreasing it. 



The French and Italian governments, after careful testing, abandoned tanks for virtu- 

 ally the same cause. 



The stabilizing tanks placed in the Imperator and her sister ship have been removed. 



Our own government instituted probably the most complete set of trials with tanks that 

 has ever been made. A vessel was equipped with no less than three stabilizing tanks — more 

 than were ever before installed — each made adjustable, and the verdict was in a rather unex- 



