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FEATHERING PADDLE-WHEELS. 
By Proressor E. M. Bracc, MEMBER. 
[Read at the twenty-fourth general meeting of the Society of Naval Architects and Marine Engineers, held in 
New York, November 16 and 17, 1916.] 
In the year 1913 tests were made in the model basin of the University of Michi- 
gan upon certain models of radial and feathering paddle-wheels. These tests were 
made for a board of army engineers appointed to investigate the question of tow- 
boats and barges for the Mississippi River. The complete report upon the subject 
can be found in House Document No. 857, entitled “Experimental Towboats.” 
Since the publication of the above report I have taken the results for feather- 
ing wheels and plotted them in a more compact form and have compared the re- 
sults obtained from the model wheels with those for full-sized wheels. 
While it is not the purpose of this paper to discuss radial paddle-wheels, it 
may not be out of place to call attention to some of the differences which exist be- 
tween the two types of wheels. As shown by Fig. 1, Plate 91, the radial paddles give 
more thrust than the feathering for the same slip, but work at a lower efficiency. 
The radial wheel has its maximum efficiency at about 10 per cent slip, while the 
maximum efficiency of the feathering wheel occurs at about 15 per cent slip. The 
efficiency for both types decreases with increase of dip but the decrease is less for 
feathering blades than for radial blades. 
In Fig. 2, Plate 91, will be found the thrusts obtained from models of feather- 
ing paddle-wheels 12% inches in diameter with blades 2 inches wide, or with a 
blade-width ratio of 0.16. In Fig. 3, Plate 92, will be found the thrusts obtained 
from model wheels 12 inches in diameter with blades 1.5 inches wide, or with a blade- 
width ratio of 0.125. Fig. 4, Plate 92, shows the effect of blade-width upon thrust 
and efficiency. The blade-width ratios most commonly used are in the neighbor- 
hood of 0.16 and from Fig. 4 it can be seen that no great error will be made if we 
assume a straight line relation between the values 0.16 and 0.125. These thrust 
values are for fresh water, and in salt water they would be 2% per cent larger. 
The efficiencies for blade-width ratios in the neighborhood of 0.16 are given in 
Fig. 5, Plate 93. The efficiencies for narrower blade-widths would be somewhat 
higher than these values. In the computations made in this paper all blade-widths 
were assumed to have the efficiencies given in Fig. 5. 
The quantities used in plotting these thrusts and efficiencies are slip at center 
of blade, eccentricity ratio, dip ratio, and pitch ratio. Fig. 6, Plate 94, shows what 
is meant by the above terms. 
Many designers of feathering paddle-wheels give the slip at the outer edge of 
the blade and assume that G (see Fig. 6) has a velocity proportional to its distance 
