14 EXPERIMENTS ON THE FULTON AND THE FROUDE. 



peculiar features. A point that Mr. Peabody did not touch on as much as he 

 should have done, is that these peculiarities are largely caused by the necessity for 

 maneuvering, backing and filling, and accelerating and retarding the movements 

 of the tug in getting up to the tow and getting away from it before you ram your 

 stern with it, and these things are of the utmost importance, especially in a tow- 

 boat used in deep sea service. If you consider a harbor tug, it must be able to 

 connect quickly with its tow, handle it smartly into its pier, must have the capacity 

 for turning quickly ; and frequently when the master of the tug finds he is going to 

 hit the tow a lick, or the tow is going to hit him, he must be able to get away from 

 it instantaneously, and that necessitates a certain type of propeller, and the effi- 

 ciency of the tug, as a whole, is largely dependent on its ability to maneuver rapidly, 

 especially in narrow waters. I think the peculiar propeller we find on the American 

 tug is also due to the fact that, until quite recently, the majority of tugs were made 

 of wood, and were fitted with ponderous stern frames and enormous rudders. 

 Every one who has experimented with tugs knows of the tremendous influence the 

 balanced rudders, made of broad wood, have on the propeller and the efficiency of 

 the propeller, especially when towing. 



Professor Wm. Hovgaard, Member: — The experiments described in this paper 

 will undoubtedly be of great value to the designers of tow-boats, but I wish to draw 

 attention to the fact that they will be of equally great value to the designers of 

 ice-breakers. 



As far as the propeller design is concerned, the two problems are about iden- 

 tical. In both cases it is required that the propeller shall develop maximum power 

 under circumstances where a great resistance reduces the speed to a very low figure. 



I have had some practical experience in the design of ice-breakers and of 

 propellers for ice-breakers, and it is a satisfaction for me to see that these experi- 

 ments corroborate the opinion which I have always held and advocated — that the 

 propellers of ice-breakers should preferably have a low pitch-ratio. I met con- 

 siderable opposition to this view of mine on the ground that the high pitch pro- 

 peller shows up better on the speed trials in free water. It seemed obvious to me 

 that a propeller, which worked under the most favorable slip at full power and 

 high speed in free water, cannot possibly work to best advantage at nearly the 

 same power when the speed is very much reduced, because the slip will then become 

 excessive. With a low pitch-ratio, a high number of revolutions may be main- 

 tained with good efficiency even at very low speeds, and thus the engine is enabled 

 to develop maximum power whereby a high thrust is obtained. 



I may mention that in the ice-breaker Sleipner, built by Burmeister & Wain 

 for the port of Copenhagen in 1895, we adopted a pitch-ratio of Ji=i.07. vShe 

 was of 2,400 indicated horse-power. 



In the ice-breaker Nadeshny, built by the same firm for the Russian govern- 

 ment for the port of Vladivostok, we adopted a pitch-ratio of 'f«i-^=i.i8. There 

 was one four-bladed propeller, of a projected area ratio of .42, somewhat smaller 



