OF SINGLE-SCREW CARGO SHIPS. 133 



take a ship proportioned such as we would like to send to sea, proportions in which we can 

 locate the machinery where we want it, that would bring us down to about 61 per cent pro- 

 pulsive coefficient, and that is comparing the shaft horse-power with the engine horse-power 

 of the model which was without bilge keel. If we add 5 per cent to that effective horse-power 

 to cover bilge keels and wind resistance, and if we take the efficiency of propulsion of the 

 reciprocating engine, which would normally be compared with this, at 90 per cent, the co- 

 efficient of propulsion, instead of being 65 per cent, would only be aibout 53 per cent, which 

 is what good practice seems to indicate today. 



The President: — Is there anyone else who desires to speak on this paper? 



Mr. W. L. R. Emmet, Member of Council: — I have no expert knowledge of the sub- 

 ject-matter of this paper, but there is something which has recently been observed which 

 seems to have an interesting bearing on the information contained in this paper. 



The General. Electric Company's men have recently built and put on a ship, on a tanker 

 of about the character of this ship described here, a torsion device which connects the shaft 

 to the propeller. This torsional device is arranged with springs and admits of considerable 

 torsional movement. To this torsional device we attached a train of connections so that we 

 could get a stationary record from the propeller under all conditions of running with a view 

 to seeing what the variations of torque in the shaft were. This shaft was being run t>y a 

 turbine, and the fly-wheel effect of that turbine was known. While we did not measure the 

 speed variations of the turbine, we knew what they were by the variation of torque. 



We sent a man to sea in the vessel. Unfortunately we did not get any very rough 

 weather, but got some moderately rough weather, four degrees of pitching, and it showed 

 an enormous variation of torque in the propeller — that is, the torque went from zero to 75 

 per cent above normal from pitching of the ship. 



Furthermore, in this ship, when this was happening the propeller was not lifted out of 

 the water. It was constantly submerged, so that the variation of torque was purely a matter 

 of the relative speed of water and propeller. Furthermore, the observation, which is being 

 verified by actual automatic records now, showed that the loss of torque was not incident to 

 the lifting of the propeller to the surface, to cavitation, or anything of that sort; it was 

 thought to have happened when the stern of the ship was settling into the water, so that the 

 water was being thrown aft by the shape of the stem. 



There is no doubt in my mind that this is what has been destroying all the gears and 

 unquestionably the conditions are infinitely worse under certain combinations of sea, because 

 these peculiar results only occasionally occur, and certain combinations of waves would pro- 

 duce two or three periods of very heavy strain. 



If we compare the facts shown by Mr. McEntee's paper with the indications which I 

 have stated, we will see that the speed relation of water to the propeller must be subject to 

 a large variation in order to create such changes of torque. The actual slip given by Mr. 

 McEntee is very large, and this slip must be overcome at one time and greatly increased at 

 another. 



Such variations cannot fail tO' make a tremendous difference in the efficiency of the pro- 

 peller, and I am inclined to think, in the case of a ship in even a moderate seaway, there 

 would be greater reason for using such characteristics as Mr. McEntee recommends than 

 in the case of a ship in smooth water — ^that is, the stem profoundly affects the action of the 



