SUPERHEATED STEAM IN MARINE PRACTICE. 195 



DISCUSSION. 



The President: — Discussion is now in order on this paper, entitled "Superheated 

 Steam in Marine Practice," by Mr. Oatley. I understand that Mr. E. H. Peabody, Member 

 of the Society, has a written discussion by Mr. Walter M. McFarland that he wishes to 

 present. 



Mr. Walter M. McFarland^ Vice-President (Communicated) : — I have read Mr. 

 Oatley's paper with much pleasure, and desire to thank him for the pleasant references to 

 the work done in superheating by my company. The Babcock & Wilcox Company. The 

 table on Plate 95 would appear to show that the first published results in almost forty years 

 were based on the performance of Babcock & Wilcox boilers and superheaters. 



This, however, is not quite correct, and it leads me to express regret that in paragraph 

 9 on page 174, where Mr. Oatley gives the names of some of the leaders in marine engineer- 

 ing who have experimented with superheaters, he omits one who certainly did as much as 

 any of those men, and who in a paper before an American society should not be omitted. I 

 mean, of course, our great engineer Isherwood, who passed away only this last summer. 



In his famous work entitled "Experimental Researches in Steam Engineering," and 

 published in two volumes in 1863 and 1865, there are records of at least five elaborate tests 

 of superheating, which were conducted with his usual care and extent. By the latter I mean 

 that the individual tests lasted for seventy-two hours each. In the case of the steamer Eutaw, 

 tested at the Washington Navy Yard in 1863, there were fifteen of these separate tests at 

 different points of cut-off, using saturated steam and superheated steam, and the test at 

 each point of cut-off and each condition of steam lasted seventy-two hours. 



It may be of interest to note here that the Eutaw had separately fired superheaters, so 

 that it was possible to vary the degree of superheat with other conditions remaining the 

 same. In these tests, where the steam pressure was about 26 pounds, with the temperature 

 for saturated steam about 270° F., the superheat varied in the different experiments from 

 87° F. to 125° F. The maximum economy shown in the experiments as due to superheat- 

 ing was about 23 per cent of the saturated steam per horse-power. 



It may be of interest also to record here that the famous steamer Wampanoag, and 

 her equally successful sister, though not so well known, the Ammonoosuc, were equipped 

 with superheating boilers. This is clearly shown in the cut opposite page 566 of Bennett's 

 "Steam Navy of the United States." These vessels were tried in 1868, during Isherwood's 

 last year as engineer-in-chief of the navy. I mention these last to show that Isherwood's 

 earlier experiments had so well satisfied him of the value of superheat that, in the greatest 

 successes of his ofiicial career as engineer-in-chief, he continued to use it. 



The query naturally arises why superheat should have been so abandoned for more than 

 thirty years, when the knowledge of its benefits was so well known. I cannot agree entirely 

 with Mr Oatley that this was due to the inferiority in materials and workmanship as com- 

 pared with existing conditions, although present conditions are, of course, a decided im- 

 provement. It seems to me that the reason is right at hand when we remember that just 

 about this time (1865-1870) the compound engine began to be used extensively, with the 

 accompanying great increase in fuel economy. As just stated, the experiments on the Eutaw 



