78 SOME COMPARISONS RELATING TO 



Maximum theoretical efficiency of Jupiter is , or 33.4 per cent. Maximum 



theoretical efficiency of the California is ^^^ , or 35.1 per cent. 



ODD 



1 7 



Under this condition, the gain in efficiency due to use of higher pressure steam is — ^, 



or 5 per cent. In view of past records quoted for reciprocating engines, it is hard to see 

 how any considerable advantage can be hoped for with this type of plant. 



Fig. 3, Plate 40, contains the coal consumption curves for the Jupiter and Cyclops as Mr. 

 Robinson gave them in answer to me last year. 



Fig. 4, Plate 40, contains the same curves corrected as far as I have been able to get 

 reliable data. It will be noticed that the curve from 10 to 11 knots for the Jupiter is prac- 

 tically level. This makes me think that Lieutenant Robinson's figures for the coal consump- 

 tion from 11 to 13 knots inclusive are in error. The four figures for the Cyclops and the 

 figures at 10 and 15 knots for the Jupiter are as reliable as it is possible to get data. 



In Fig. 2, Plate 40, are shown speed and power curves for the two ships. I wrote for 

 official figures from the Department, but have been unable to get the data. These curves have 

 been constructed by comparing with the cube of the speeds. The accuracy of this method 

 is shown by the fact that the shaft horse-power of the Jupiter figures out 2,125 and is given 

 by trial as 2,015. This proves that the shape of these curves cannot be far out, and the upper 

 points are fixed by trial trips. The trial of the Cyclops gave 6,705 indicated horse-power 

 at 14.67 knots. I understand that it is the practice of the Navy Department to consider a 

 new engine to have an efficiency of 90 per cent. This will give the shaft horse-power of the 

 Cyclops as 6,034 in place of the 6,705 indicated horse-power. The Cyclops and Jupiter are sis- 

 ter ships and are designed to drive at 14 knots with 5,500 shaft horse-power. The shaft 

 horse-power of the Jupiter by torsion meter was 5,830 and for the Cyclops was 5,370, both 

 from the curves. 



Without going into this matter in great detail I question the torsion meter results. 

 Lieutenant Robinson told us that the Jupiter had the better propellers. I feel that we are at 

 least entitled to assume that the propellers were equal. If this be so, then the speed and 

 power curve of the Cyclops is more accurate for the Jupiter than the results given by the 

 torsion meter installed on the Jupiter. I have taken this curve and, by comparing with 

 the coal consumption curves, have constructed the efficiency curves shown in Fig. 1 , Plate 

 40. The efficiency here represented is service efficiency. If Lieutenant Robinson made an 

 error in the coal consumption for 11. 12 and 13 knots speed, the Jupiter's curve could be 

 flattened out to assume a shape more like the Cyclops. However, this shows that the Jupiter 

 is the better ship at cruising speeds. We can question steam consumption, but we cannot ques- 

 tion coal consumption. This is one of the points which I always try to get to. In this way 

 all classes of prime movers can be compared. The comparison is final. Then by doing 

 this a better idea of possible gains or losses can be arrived at. 



It may be said that it is of little importance whether the torsion meter is correct or not. 

 There is another point to be considered. In this case the plant is being sold by torsion meter. 

 For this reason it becomes of utmost importance that the torsion meter be accurate. I feel 

 that I have more reason to state that the curve for the Cyclops is correct for the Jupiter 

 than an opponent can have for insisting upon the accuracy of the torsion meter. 



Correcting for this error in the torsion meter we find that the steam consumption at 10 

 knots becomes 12.65 pounds in place of 12.316, and for 15 knots 11.68 pounds becomes 

 12.95 or perilously near the guarantee of 13 poimds. 



