EXPERIMENTS ON THE FROUDE. 107 
Having rated the Pitot tube it was used to register the speed of the 
Froude through the water when towed by the tug-boat Wm. G. Williams, 
which is about 62 feet long and has a draught of about 6 feet. The tow-line 
was 200 feet long and in all cases was kept clear of the water; a light line 
was used for low speeds and a heavier line at higher speeds. The race of 
the propeller was distinctly felt being about 5 per cent. at 6 to 7 knots. 
The resistances at various speeds are shown by Fig. 25, Plate 56, which 
gives in all three curves: (1) the proper corrected curve of resistance on 
speeds; (2) the uncorrected curve of resistance on the indicated speeds by 
the Pitot tube, and (3) the resistance as estimated from the model (23.5 
feet) when towed in the Washington Model Basin. The latter curve was 
determined by applying the theory of similitude on the basis of displace- 
ment, not making separate computations for frictional and residual resist- 
ances. The discrepancy between our experimental curve and the curve 
deduced from the 23.5-foot model is not more than may reasonably be charged 
to the difference in surface; the hull of the Froude was planked and caulked 
and painted with antifouling paint, while the model had a fair double skin, 
painted and varnished. 
BRAKE TESTS OF I9QII. 
A brake with a cast-iron wheel 10 inches in diameter and having a 
face 8 inches wide was attached to the propeller shaft at a convenient place 
and arranged for continuous water cooling so that it could run steadily 
at any given condition half an hour or more. The brake arm was 30 inches 
long and pulled on a spring balance that could be read to one-half pound; 
the load varied from 10 to 95 pounds for the several conditions. 
A complete investigation was made for each of the three propellers 
having the three several pitches mentioned in this report; because the 
revolution corresponding to a given power varied with the pitch. Having 
the input to the motor for a given power and speed and the brake reading 
for those conditions, the shaft horse-power could be found directly, without 
depending on a rating of the motor. Fig. 26, Plate 57, gives the tests by 
the brake for the conditions of Propeller No. 1, both for the normal con- 
ditions and when the Froude was used as a tow-boat. 
ACKNOWLEDGMENTS. 
As was said at the beginning of this paper the tests on the Froude were 
proposed and financed by Dr. Charles G. Weld and this addition to our 
knowledge of the problems of propulsion is due primarily to him. 
