136 PERIOD OF VIBRATION OF STEAM VESSELS. 



Captain Smith : — That is believed not to have had a very great deal of effect. That 

 has not been thoroughly worked out yet, but it is not taken into serious consideration. As 

 I understand, they will reinstall the three-bladed propellers instead of the four-bladed pro- 

 pellers. 



Mr. Lovekin : — I had the pleasure of talking with Captain Dyson the other day, and 

 he informed me that the vibrations had been materially reduced, to his amazement, that 

 the power had exceeded the old three-bladed screw, at 3,000, and that he would recommend 

 that the three-bladed screws be put back to take care of the vibration. 



Captain Smith: — Mr. Lovekin evidently has later information on the subject than 

 I have. 



The Chairman : — The Chair was about to remark that certain intimations have come 

 to him somewhat at variance with the conclusions reached by Captain Smith. It appears 

 to the Chair that it would be very desirable to have in the Society's Transactions the actual 

 conclusions of the Board recently appointed by the Navy Department to consider thoroughly 

 the subject of propeller shaft fractures, and I trust that will be accomplished before our 

 next meeting. I understand that some of the results of their investigations were exceed- 

 ingly interesting and show conclusively where we may look for these troubles. As I am 

 not fully informed personally as to the details, I would prefer to hear from those who 

 have had direct touch with the matter in its latest phases. I have no doubt that Captain 

 Smith's information is based quite correctly on some of the preliminary work of the Board. 

 It may be possible, however, in the final conclusions, based on results obtained from com- 

 plete experiments, that there may be some modifications. 



Mr. John Reid, Member: — In the case of the Mauretania, about a year after she came 

 out, they changed from three-bladed to four-bladed screws, which greatly reduced the vibra- 

 tion and changed the whole nature of the vibration. I used to go into the tunnel very 

 often to see what was happening, and if you went close to one of the two aft screws you 

 always found a curious action going on, especially in stormy weather, and that was the 

 thrashing of the water against the ship's side, abreast of the screw, seemed to grow. The 

 screw would go around freely for a few revolutions, and then there would be a crash of 

 water against the side of the ship that seemed to grow larger and larger and then stop. 

 I think that was a matter of torsional vibration of the shaft, but do not know enough 

 about the subject to go into it from a mathematical point of view. I know that the 

 changing of the screw did make a tremendous difference. As to what it did with the speed, 

 I think that was also improved. 



The Chairman : — The opinion of the Chair is that Mr. Reid has "hit the nail on the 

 head," and that ultimate results of investigation will indicate that it was mainly due to tor- 

 sional vibration of the shafts; but I think it is wiser to have the complete results of the 

 investigations recently undertaken and then members can draw their own conclusions. 



Mr. Francis B. Smith, Member: — May I make another remark on the subject of 

 vibrations. It may be of interest to some of you some time. We have had a couple of expe- 



