20 RESISTANCE OF BILGE KEELS. 



But there is another factor present. There is a case of a United States battleship which 

 some time ago was tried with bilge keels. The bilge keels were afterwards removed and 

 the ship was tried over the same course, same displacement, same conditions as nearly as 

 possible, and the ship took materially more power for a given speed with the bilge keels ofif 

 — it was a matter of several hundred horse-power — ^and although the experiments were not 

 of a high order of accuracy there was no doubt that there was more power taken when the 

 bilge keels were off. That was something of a puzzle, but the answer, I think, is compara- 

 tively simple — the vessel did not steer nearly so well after the bilge keels were removed, and 

 in running a trial, in trying to keep the ship to a straight course, they used more helm with 

 the bilge keels off than with the bilge keels on. It takes only a very few degrees of helm to 

 produce a very decided drag on the vessel and increase the resistance. It has occurred to 

 me that possibly the use of a helm may explain some of the discrepancies in these experi- 

 ments, as this boat was tried in open water and they necessarily had to use a helm to keep a 

 straight course. That is a factor which is ignored sometimes, but not ignored by the con- 

 tractors when they want to get the best speed on a trial trip. They always use a good 

 helmsman and see that he uses as little helm as he can possibly get along with. 



The Chairman: — Is there any other gentleman who desires to comment on the paper? 

 If not, we will ask Professor Pealbody to make such reply to the discussion as he cares to. 



Professor Peabody : — The experiments were carried on here, not only with the normal 

 bilge keel, but with a bilge keel which was three times as deep as a normal bilge keel, and 

 that the reports are based upon an investigation of all our experiments, the actual com- 

 putation having been based upon the deepest keel, namely, 9 inches, but the curves on 

 Plates 19 and 20 will show, particularly on an average from one curve to the next, that 

 whatever we could attribute as the increase due to the 9-inch keel could be assumed to vary 

 in that proportion for the 3-inch keel. I believe that, even if my wording is not as good as 

 I would like, that you get the conception. 



Now we have found also that with the best work that we can do it is very difficult to 

 determine the amount of resistance closely enough to assert, from the experiments on the 3- 

 inch bilge keels only, that the resistance did or did not increase proportional to the friction. 

 We put on the 9-inch bilge keels purposely so that we should be able to get a better determina- 

 tion. We also extended the bilge keels to make them long, some 19 feet long instead of 15 

 feet long ; and I report no result, because we got no result ; namely, we got practically the 

 same thrust and power with and without these extensions to the bilge keel. If we compute 

 the added resistance for the increment in length of the 3-inch bilge keel, we will find that 

 amounts to about lj4 pounds, and our thrust mechanism will move with an increase of 

 about 2 pounds, and so you will see that getting this result does not signify very much. 



As to the question raised by Mr. Sperry, I may note that the prototype of the Fulton is 

 the Sotoyomo, a navy tug, with an approximate speed of 10.3 or 10.4 knots per hour, and 

 that the curves given on the several plates, which extend only to 6.5 knots, are in the proper 

 relation, by the theory of similitude, so that these diagrams show the dispersion at the com- 

 mercial rates. But I believe it to be practically impossible to propel the Fulton, with any 

 development of power you can put into her, up to 15 knots. What the curves would do 

 in that case would be difficult to predict, and not particularly useful. 



