NOTES ON FUEL ECONOMY. 239 



reasons for that. The design that won out was 25 feet shorter than the longest 

 one, and I can also tell Mr. Rigg that the firm with which he is connected were just 

 about 10 feet longer than the successful one. That all comes back to this: That 

 in a cargo boat the prismatic coefficient amounts to little or nothing, because we 

 all of us would make the boat a box amidships if it were desirable. You have got 

 to have so much dead -flat length and when you come to the ends what can you do ? 

 You probably have one-sixteenth of the length at each end that must be fined. 

 A hundred designs could not vary much in the fining the ends within that limit, 

 which brings us back to the engineering feature. If one boat does better than the 

 other it is due, in all probability, to a better design of the propeller and the run of 

 the vessel. In my opinion, to give examples of freight boats, and to bring in the 

 prismatic coefficient is begging the question. It may be all right in the case of a 

 battleship. Let me show you where it comes in in the case of a battleship. I do 

 not think I am giving away any state secrets in mentioning the Rivadavia and 

 Moreno. A certain firm took those boats. The speed-length ratio was increased 

 at the last moment. They wanted more speed. Three feet on the beam of the 

 boat enabled the prismatic coefficient to be reduced and the ends of the ship to 

 be correspondingly fined, and if these boats are a speed success it is due to the change 

 referred to, but of course this is dealing with a 22.5-knot vessel. On the other 

 hand, if Mr. Taylor, to whom Mr. Rigg refers, had been asked how he could econ- 

 omize horse-power with usual proportions in a cargo steamer of .79 or .80 block 

 coefficient, I am afraid he would admit that little if any appreciable saving could 

 be made. 



Mr. Thomas M. Cornbrooks, Member: — In connection with the example 

 on page 231 regarding Mars class, I desire to make a correction in the statement 

 made by Mr. Rigg. I note Mr. Rigg gives the credit for the performance of this 

 vessel to the experimental model basin, while Mr. Simpson claims the credit for 

 himself; neither statement is entirely correct. In the first place, the keel of this 

 vessel was laid in October, 1908, the model was tried in the basin in March, 1909; 

 consequently the trial had no influence on the lines. 



Mr. Simpson states that the Mars class is a copy of the Everett. While the 

 outboard appearance of these vessels are similar to the Everett, I cannot see how 

 the appearance would affect the economy. The lines for these vessels were designed 

 by the company with which I am connected and the credit for the performance 

 belongs to them. 



It is evident that Mr. Rigg is a great believer in the experimental model basin, 

 and it is to be regretted that he did not secure more reliable data in regard to some 

 of the examples which he presents. 



On page 234 he speaks of a Sound steamer which has recently been designed 

 and makes a very broad statement in reference to indicated horse-power and saving 

 in coal bills. I would Uke to ask Mr. Rigg whether his conclusions are based on 

 model experiment or on theory. The difference in indicated horse-power shown 



