OF SINGLE-SCREW CARGO SHIPS. 135 



horse-power, as the term is most commonly used. Accurate trial data giving power and 

 propeller revolutions and speed over a measured course under ideal conditions are very 

 meager. However, attention is invited to last year's paper and to the discussion of the same 

 by Rear Admiral C. W. Dyson. Admiral Dyson has collected data from the actual trials 

 of ships for use by him in designing propellers. I asked Admiral Dyson to prepare some 

 estimates for the ships represented by the models in last year's paper, which he kindly did 

 and included in his discussion. The estimates prepared by him checked remarkably well 

 with the results of the model tests. It must be remembered also in discussing propulsive 

 ei^ciency that the results here given do not include shaft friction or loss in the thrust 

 bearings. 



That a propulsive efficiency as high as 65 per cent may be obtained in the ordinary 

 cargo ship, with propeller running at about 90 revolutions per minute, seems to be confirmed 

 by experiments along a somewhat similar line by Mr. Semple in England. A reference to 

 his work is given in the body of my paper. 



I was very much interested in the comments of Mr. Emmet, especially as to the varia- 

 tion of torque encountered at sea when a vessel is pitching. Though this variation undoubt- 

 edly must contribute to some cases of failure of reduction gears installed for ship propul- 

 sion, I ami inclined to think that an equal number of failures may be ascribed to torsional 

 vibration of the propeller shaft. 



The President : — This is a practical paper. Taken in connection with the paper of 

 yesterday by Mr. Robertson, it gives all those who operate ships food for thought. Although 

 the paper is expressed in scientific terms, it has an exceedingly practical bearing. The com- 

 ments of Mr. Robertson, Mr. Emmet, and Professor Sadler are supplementary and illumi- 

 nating. We would like to hear something from any ship operating representative. 



In the absence of further discussion, I am sure you will permit the Chair to present 

 the thanks of the Society to Commander McEntee for his paper. It is most admirable in 

 substance and form. It has had, besides, an illuminating discussion. 



The next paper is entitled "Buoyancy and Stability of Troop Transports," by Professor 

 William Hovgaard, Member. 



Professor Hovgaard presented the paper. 



