PERIOD OF VIBRATION OF STEAM VESSELS. 135 



Mr. Francis B. Smith, Member: — I just want to make a few remarks based on some 

 practical observations of vibration on ships of the class we have on the Lakes — long ships, 

 about 600 feet long, 60 feet beam, and about 32 feet depth. We sometimes get reports 

 of a ship vibrating very badly, and we have had occasion to try to locate this difficulty. We 

 have not found any cases yet on our ships where we could not take the vibration out — that 

 is, all perceptible effects of the vibration — by regulating our engines and the trimming of the 

 ship with water ballast ; it is very seldom that we have to go to the water ballast unless we 

 find it has been improperly distributed. 



We have had a number of cases where we have had men who made a profession of bal- 

 ancing engines go with us, and in following out their recommendations we probably have 

 improved the trouble somewhat, but it has been our experience, in our class of ships, with 

 the machinery and boilers located away back in the stern, where it is probably difficult to 

 place them, that we are generally able to bring it down to a point where it does not do any 

 injury to the ship, simply by balancing the engine in regulating the cuts of the different 

 engines. That has been our experience. 



Captain Albert P. Niblack, U. S. N., Vice-President: — I wish to make a few re- 

 marks merely on the importance of the question of the vibrations on board a battleship. 

 The question is of vital importance, because the period of vibration of ships being neces- 

 sarily different, it is quite conceivable that in a formation of battleships, the speed at which 

 the formation is steaming might commit one ship to a vibration that was ruinous, in the fact 

 that the vibration might disturb all observations of any kind — for instance, of range find- 

 ing, gunsights, and fire control. The question is really with us a very vital one. 



With a merchant ship you can take the necessary precautions to change the speed, but 

 when you are in formation, as in the case of battleships, you cannot change the speed, and 

 the admiral in command of a fleet possibly does not know that the other ship is vibrating. 

 I want to bring up the point that probably by regulating the ballast by using trimming 

 tanks, the vibration could be regulated even on a ship that found herself in this unfortunate 

 position. 



The helpful point that has been brought out by this paper is the practical application of 

 a remedy and I thank Mr. Gatewood for it. 



Captain W. S. Smith, U. S. N., Member: — The Department recently conducted some 

 experiments of vibrations on battleships, and being familiar with them, I will state practi- 

 cally what has been done and some conclusions reached. 



In the case of the Minnesota, a battleship which suffered a great deal through the 

 breaking of shafts, a Board was appointed and the subject very thoroughly gone into. 

 Experiments were made, and the machinery was put in perfect alignment so as to eliminate 

 as much as possible any question of engine vibration by being out of line. The vibrations 

 were measured, and the general determination reached was that stiffening, particularly under 

 engine foundations, and with a due regard to the design of the shaft to make it heavy enough, 

 would obviate the trouble — that is briefly the conclusion arrived at in the study of vibra- 

 tions recently made. The question of thrust bearings was gone into, and they were supposed 

 to be very thoroughly stiffened up through the inner bottom. 



Mr. Luther D. Lovekin, Member: — I ask Captain Smith if the question of the four- 

 bladed propeller did not have an effect on the vibration of the vessel? 



