ENGINEERING PROGRESS IN THE U. S. NAVY. 73 



the expected improvements in both propulsive efficiency and turbine efficiency will 

 be realized. Regarding the first point, experience had with screw designs since 

 those of the North Dakota were made shows that their design can be materially 

 improved, even without changing the revolutions. The expected gain due to 

 better design, combined with lower revolutions, has been arrived at after consul- 

 tation with Captain Dyson and his assistant, and I believe that the figure assumed 

 is regarded as quite conservative. 



Concerning the expected gain in turbine efficiency, a fear has been expressed 

 that sanguineness may have induced expectations that cannot be reached. In 

 answer to this I will state the grounds on which the expected improvements are 

 based. 



First. In the old North Dakota turbines there are 28 moving rows of buckets. 

 In the new turbines there will be 97 rows. Although the peripheral speed is some- 

 what less in the latter, the efficiency is certain, judging from previous experience 

 with actual machines, to be much better. 



Second. The methods of calculation employed in arriving at the figures are 

 founded upon constants which have been used extensively in this country and 

 Germany, and also in England and France, and which have been shown to be reli- 

 able by application to many different types of turbines. The correctness of these 

 methods has been confirmed by an immense practical experience in these countries 

 with both the Curtis and Parsons turbines, including marine types. 



Third. The results shown by a cruiser having turbines very similar in character 

 to those under consideration, but of less horse-power, which were tested with great 

 thoroughness during the builders' trials of the vessel several years ago. At 14.2 

 per cent of full power (corresponding with 12 knots) and a peripheral speed of 73.5 

 feet per second, the expected water-rate in the case of the new North Dakota is 

 16 pounds. Under similar conditions, but at considerably lower peripheral speed, 

 and with fewer rows of buckets, the cruiser turbines show a water-rate of 17.1 

 pounds. At the same peripheral speed, they would have shown a water-rate fully 

 as low as 16 pounds. The results shown by these cruiser turbines would of them- 

 selves seem to warrant full confidence in obtaining the results expected. 



Fourth. Within the last year a number of large battleships have been ordered 

 by some of the most advanced nations to be equipped with Curtis turbines of a 

 similar character. In England a large battleship cruiser of 85,000 horse-power 

 has recently been ordered fitted with Curtis turbines quite similar in character, 

 and involving figures of economy quite as low relative to the conditions as those 

 now proposed. As already stated, responsible builders have for some time been 

 offering designs with assurances of economy at low power for battleships similar to 

 that now under discussion, practically on a par with the figures shown by the 

 Delaware. 



Fifth. With four-shaft arrangements still better economies can be obtained. 



I do not mean, of course, to predict that the exact estimated figures will be 

 obtained. Every experienced engineer knows that in a machine of this kind the 



