14 RESISTANCE OF BILGE KEELS. 



The several curves of propeller thrust in pounds on speeds in knots per hour 

 for experiments on the bare hull and with the 3-inch, 6-inch and 9- inch keels (all 

 of normal 15-feet length) as given on Plate 19 were constructed from the proper 

 curves of speeds on revolutions and from the accepted standard curve of thrust 

 on revolutions. The thrust curve is that shown on Plate 15, and Plate 14 shows the 

 curve of speeds for the normal 3-inch keel. Plate 19 is consequently a resume of all 

 the experiments on the normal length keels. 



Plate 20 gives the power input in kilowatts to the electric motor for all ex- 

 periments on the bare hull and for keels of normal 15-feet length, derived from 

 curves like those on Plates 14 and 16. From these curves and from brake tests 

 made in 1912 the horse-power applied to driving the propeller shaft has been 

 computed and also used as a basis of determining the effect of the keels. 



The main dimensions of the Fulton are as follows : — 



Length, load- water-line, feet 30.9 



Beam, feet 7 



Draught, mean, feet 3.25 



Displacement, tons fresh water 9.6 



Normal speed, knots per hour 6.4 



Wetted surface, square feet 298 



The bilge keels had the following lengths measured at the middle of the depth : 



Three-inch keels 15 teet 2.5 inches 



Six-inch keels 15 feet 4 inches 



Nine-inch keels 15 feet 5 inches 



The wetted surfaces, including edge (% inch), were as follows: — 



per cent. 



Three-inch keels, square feet 17. i 5.7 



Six-inch keels, square feet 32.4 10.9 



Nine-inch keels, square feet 47.8 16. i 



The per cents given are those of the keel areas to the wetted area of the bare 

 hull. 



The bow and stern extensions of the 3-inch keels were each 2 feet long. The 

 surface of all four was 4.5 square feet. 



The most direct , experimental determination of the resistance of bilge keels 

 can be made from the increment of thrust of the propeller shaft, above that re- 

 quired for the bare hull. 



Taking first the 9-inch keels, since we are dealing with small differences, we 

 may deduce the following table : — 



