240 NOTES ON FUEL ECONOMY. 



is 500. Figuring from Mr. Taylor's curves the effective horse-power for each vessel 



works out as follows: — 



"A" "B" 



Frictional 831 837 



Residuary 666 654 



Total effective horse-power 1.497 i.49i 



at 50 per cent efficiency equals " A " — 2,994, and " B " — 2,982 indicated horse-power, 

 or a difference of 12 indicated horse-power. 



Constructor Taylor says, in regard to "The Influence of Midship-Section 

 Shape upon the Resistance of Ships:" — 



"The shape of the midship-section has a comparatively minor influence upon 

 the speed, and that the midship-section coefficient may range from .85 to i, with 

 very Uttle effect on speed, and may be made as low as .70 without a material 

 increase in resistance. 



"Also increased beam means increased disturbance of at least a portion of 

 the water which a ship passes." 



In view of the foregoing, it is difficult to see where Mr. Rigg secures a saving 

 of 18 per cent in the coal bill. 



Mr. Rigg : — Referring to Mr. Chace's request for more data concerning the 

 examples given; taking them in order the following can be stated: 



Example No. i. — Curves of effective horse-power cannot be given, for the first 

 ship they do not exist, and for the Mars, though the model was run, I am not in 

 possession of the curves. The curves of indicated power are given in the text of 

 the paper. 



Example No. 2. — It is probable that the residuary resistance of the 370-foot 

 ship would be too high for general ocean work. She was designed for short coast- 

 wise runs, comparatively close in shore, and the chances of being badly slowed up 

 not as great as off shore. The example was suggested by an actual design coming 

 up in the ordinary course of business and worked up from published tank test data, 

 and not from actual tests for the two boats. 



Example No. 6. — Additional data connected with this vessel has been incor- 

 porated in the body of the paper. 



Example No. 8. — I am glad Mr. Chace agrees with me, because Mr. Cornbrooks 

 decidedly does not. I will refer to this vessel later. 



Referring to Mr. Simpson's remarks, on looking over my freighter examples, 

 I am unable to find any reference to the prismatic coefficient ; nevertheless, though 

 the range of choice is limited in full models, the prismatic coefficient is still of 

 importance. The object of Examples Nos. 2 and 3 is to show what can be done 

 by judicious shortening of the ship, always watching for the point where the 

 residuary resistance begins to increase too rapidly. 



