8 EXPERIMENTS ON THE EULTON AND THE FROUDE. 



Plate 8 gives for one of our series of towing experiments individual 

 points and curves showing speed, power, propeller thrust, and tow-line puU, 

 all plotted on revolutions of the propeller. The curves of thrust and power" 

 call for little comment unless we notice that the greater apparent dispersion 

 of points is partly due to the fact that wind had relatively larger effort on 

 account of slower speed. 



As was explained in the preliminary statement the speeds during towing 

 were measured by a little propeller 8 inches in diameter and with 14 inches 

 pitch, which was carried by a bow outrigger so that its axis was 9 inches 

 below the water level and 8 feet in front of the stem of the boat. Though 

 this propeller log showed good results on special runs without a tow over 

 the measured course, its operation during towing was less satisfactory, chiefly 

 because as the season advanced we found it necessary to accept weather 

 conditions less favorable than we would like, trying to minimize wind influ- 

 ence by choosing sheltered parts of the basin. Several runs were made 

 in succession with the wind, followed by others against the wind. In drawing 

 the fair curves greater weight was given to points which our records indicated 

 as more reliable, and especially to points favored by shelter or other weather 

 conditions. If two points which are apparently rather wide from the speed 

 curve, and which v/e believe to be erratic, are neglected, the dispersion of 

 points indicates that the probable error of speed measurement of a single 

 test may be as large as four per cent, but we believe that the mean curve is 

 much nearer the truth and we desire to claim a precision of two per cent, 

 which, after all, is not unfavorable considering that towing is at low speed. 

 The dispersion of the points showing thrust and pull on tow-line is a direct 

 consequence of the uncertainty of speed. 



Plate 9 shows points and curves of pulling tests with the tow-line 

 secured to a pile of Harvard Bridge. Going ahead the weigh-beam was 

 set up astern, but in backing it was set up near the bow. All these runs 

 were made readily and in particular there was no indication that the race 

 from the propeller had any tendency to break. Our thrust mechanism did 

 not allow of measurements while backing. It must be admitted that the 

 points and curves leave little to be desired and that the records can be 

 accepted without reservation. 



Certain subsidiary experiments wiU be reserved for future discussion 

 to avoid confusion. 



RUNNING FREE. 



The performance of tow-boats of the ocean-going and harbor type may 

 be discerned from Plates 47 and 49 of volume 15 of the Transactions and 

 from Plate 9 of this paper. 



