106 EXPERIMENTS ON THE FROUDE. 
4 inches abaft the fair-water; that propeller followed one with a longer 
hub so that if by oversight the propeller shaft was not drawn back into the 
hull the propeller might have such a position. 
It has not been possible as yet to analyze the tests of this year for wake, 
thrust-deduction and hull-efficiency, but the conclusion that changes of 
projected area-ratio and pitch have comparatively small effect on propeller 
performance is so inevitable that it is thought desirable to present so much 
of our work as is now ready; there remains a considerable amount of work 
done on the Froude acting as a tow-boat which must go over to some future 
meeting and at that time advantage may possibly be taken to amplify the 
report of this year. 
In order to emphasize the fact that propeller changes have small effect, 
Fig. 22, Plate 53, has been drawn for propellers No. 1, No. 2 and No. 3 at 
the normal setting. The previous figures show that the power curves were 
but slightly affected by width of the blade; consequently one mean curve 
has been drawn for each pitch; these three mean curves show surprisingly 
small variation. A similar diagram for the 12-inch settings would show 
even closer concordance. 
Now the variations of both pitch and width of blades are much greater 
than are likely to be assigned to any given design even by engineers who 
differ widely in practice, consequently we may conclude that the practical 
efficiency of well designed propellers is very little affected by ordinary 
variations of pitch and width of blades; to this conclusion may be added that 
all propellers having oval forms of blades are sensibly equal in efficiency. 
It is thought that it would be interesting to show two typical diagrams 
with all observed points recorded; one, Fig. 23, Plate 54, represents tests 
made on a day when there was no appreciable wind; the other, Fig. 24, 
Plate 55, represents tests made when the wind varied from east to north 
in three hours, and blew at times with a velocity of 7 knots per hour. 
TOWING OF THE FROUDE. 
A direct determination of the resistance of the Froude was made by 
towing with the propeller removed, but otherwise in normal condition. 
In anticipation a Pitot tube and a registering gauge was fitted; the tube 
which was three-quarters of an inch in diameter and had a hole one-fourth 
of an inch in diameter, was protruded directly down 12 inches below the 
planking under the center of buoyancy. The tube and gauge were rated 
by running the Froude a large number of times (160) over the measured 
course taking times in the usual way by the recording device. 
