COMPARATIVE RESULTS IN STEAM AND COAL CONSUMPTION. 189 



as to the care and accuracy with which they were performed. I know there are 

 some others present who were also present at the tests. 



In regard to the question of bad coal, our evaporation per pound of coal works 

 out a little better than nine and a half pounds. Now, members of this society may 

 have had much better results with steam coal, even with picked steam coal; I for 

 one have not. I find more tests where the evaporation runs at eight pounds than 

 I do at nine and a half. So far as the speed is concerned there is no question that 

 in making this speed we made a sacrifice of from a knot and a half to two knots of 

 our maximum speed. Whether this could have been avoided is not the question. 

 I think anyone who will look at the sizes of the propellers, the relative pitches, will 

 see that it was perfectly impossible to run at a very much higher speed without 

 overspeeding our center engine, and still have it running correctly for our thirteen 

 knots. We made a trial of allowing live steam to go directly into our low-pressure 

 turbines, and got very close to fifteen knots, but it was not a feasible working 

 arrangement excepting for a sttmt. 



Now as to economy on very much reduced speed. Apparently, the turbines 

 are doing less and less work as you reduce the pressure on the center engine. You 

 can notice that if you will look at the slip curve on Plate 61. You will notice that 

 at ten knots the turbines are showing ten per cent, negative slip. If, however, you 

 will look at the speed revolution Curves i and 2, just above. No. i being for the boat 

 driven by the center engine only, No. 2 the revolutions of the center engine when 

 working in combination, you will see that even at these reduced slips the turbines 

 are still helping, and if they did no more than turn around without resistance they 

 still would be of advantage at the regular cruising speed. In this ten-knot condi- 

 tion, there was about 10^ to 11 inches vacuum in the turbine receivers. 



In regard to what Col. Stevens said about the indicator cards, the procedure 

 was to take three sets of cards on each run, to figure the cards on the basis of the 

 mean revolutions of the run, plot the individual spots and fair the curve through 

 those spots. Undoubtedly, in the lower speed runs, the low-pressure card is not 

 telling all the truth. I think anyone familiar with indicators will know how 

 difiicult it is to touch even lightly on a low-pressure card and not to have it inter- 

 fere with the action of the indicator. 



Perhaps it would not be amiss to have me say that our experience with the vessel 

 in the three conditions has been that in general cruising with adverse weather, with 

 storms, our speed fell off very much more with the turbines than it has since we 

 have had a large propeller to help us out. 



The comparative tests were all run in summer weather conditions, smooth sea 

 and clean bottom. In actual service the economy in coal is very much greater 

 than is shown by these results. 



Mr. George H. Bates, Member (Communicated) :— In reply to Mr. Crane's 

 request that one of the members present at the trials of the Vanadis testify^to the 



