EXPERIMENTS ON THE FULTON AND THE FROUDE. 7 



namely, that the width of blade and the projected area-ratio of a propeller 

 have little or no influence on the performance of a tow-boat when (i) running 

 free, or (2) towing. The evidence with regard to pulling is incomplete, but 

 I believe that with a pitch-ratio not greater than 1.3, a moderate area-ratio 

 will avoid breaking the race. It is to be borne in mind that our least area- 

 ratio is 0.44, which is nearly a fourth greater than the developed area-ratio 

 that has been found sufficient for general service. 



This conclusion, if accepted, has a wide importance because it indicates 

 that the best propellers for tow-boats have a well-rounded or oval blade and a 

 moderate width. There appears, therefore, to be no reason for retaining the 

 traditional tow-boat propeller with its excessive area and wide-tipped blades, 

 more especially as Froude's recent experiments show that such wide-tipped 

 propellers are about three per cent less efficient than well-rounded blades. 



This separate, preliminary investigation of the effect of blade area (or 

 rather of its ineffectiveness) clears the field and allows us from now on to 

 concentration on other elements which have determining effects. 



EXPERIMEJNTS ON THE) PULTON, I912. 



Three types of experiments were made this year on the Fulton: (i) 

 running free, (2) towing at various speeds up to about 0.6 full speed, 

 and (3) puUing, both going ahead and backing. Three propellers were used, 

 all of which had very nearly the same projected contours as the Sotoyomo 

 propeller as shown on Plate 2. 



In order to present the quahty of our work and the regularity of results 

 obtained, an individual diagram for each type is given by Plates 7, 8 and 9 

 with all the points representing separate experiments as well as with fair 

 curves. Thus Plate 7 shows curves of speed, propeller thrust and brake 

 horse-power, all plotted on revolutions of the propeller. For both speed and 

 thrust there are curves with and against the wind; the power for a given 

 setting of the machinery is not appreciably affected by the wind under the 

 favorable conditions selected for experiment, and only one curve is drawn. 

 On this plate the power is the input to the motor in kilowatts which is after- 

 wards corrected by comparison with our brake tests to given brake horse- 

 power as used in the other plates. It may be claimed that the regularity 

 and distribution of points for these experiments leave little to be desired, and 

 a comparison with standardization of full-sized ships in a tideway under 

 such weather conditions as may chance to be experienced will lead us to 

 wonder that such tests are as good as they are, rather than that they are not 

 more nearly what we would desire. 



