104 EXPERIMENTS ON THE FROUDE. 
conditions more nearly like those of ordinary practice for steamships. This 
fair-water was 5 inches long and added just so much to the length of the 
boat. It is thought that it had but a small effect on the resistance of the 
hull. The fitting of this fair-water required the use of twin rudders to clear 
the propeller. 
Two improvements in the apparatus were: (1) the substitution of a 
wattmeter for the ammeter and voltmeter of the previous year so that the 
observer had but one reading to take instead of two, and the placing of a 
water-cooled friction-brake on the propeller-shaft inside the hull. 
An attempt at direct determination of the resistance was made by 
towing the hull without a propeller. 
The main object of this year’s investigation was the determination of 
the influence of the pitch and area of the propeller, on propulsion. For this 
purpose three propellers were made each 2 feet in diameter and with a 
projected area ratio of about 0.6 of the disk area. Except in the detail of 
blade contour these propellers followed the type tested by Naval Constructor 
Taylor and reported to this Society in the years 1904 to 1906, and in par- 
ticular the blades were very thin, the thickness ratio being 0.04; as shown 
in Mr. Taylor’s papers, moderate variations of blade contour have little 
if any effect on performance. Three pitch ratios were chosen, one normal, 
and the other two abnormal, one being much less and the other much greater 
than obtains in practice. ‘These propellers are represented by Figs. 12, 13, 
14 and 15, Plates 46. All were accurately planed by the Fore River 
Shipbuilding Company on the face and were carefully ground to a fair form 
at the back with sharp edges. They were, however, not formed as correctly 
at the back as were the propellers tested at the Model Basin and minor 
irregularities in some of our work may perhaps be in part traceable to this 
fact. After using these propellers at the area-ratio given above, they were 
cut down and the backs esopenly shaped to give the projected area-ratios 
shown in Table III. 
The axial dimensions of the blades of the propellers varied with the 
pitch and consequently the length of the hub varied in a like manner as 
shown by Figs. 13 to 15, Plate 46. The helical width of the blades varied 
to a considerable degree in consequence. ‘The propellers No. 1 and No. 3 
were set with their hubs an inch abaft the fair-water; propeller No. 2 had 
only one-eighth-inch clearance. In consequence the propeller with the 
greater pitch was bodily somewhat farther aft. All of the settings, however, 
corresponded roughly to the 6-inch setting of 1910 which was out of the 
eddy of the stern-post; and for a setting in such a position Fig. 11, Plate 45, 
shows that there is little effect from moderate changes in axial positions. 
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