13 



Fig. 3, being the curve BT, and the corresponding values of v 

 are shown in addition. This curve, even when, as in the figure, 

 R4> is so large as o-o8 of i?$2, differs but little from TT till a 

 point about two-thirds of the way in from the circumference 

 to the boss is reached. Only about a fourth of all the water 

 passes through the space inside this ; it would be exactly a fourth 

 but for the slight increase in v, amounting to about one-seventh 

 of its value at the greatest, and for all cases where R<f> is less 

 than 8% of R£l it is much less than this. A small portion of a 

 Table of Horse Power, corresponding to the case where R&=zK 

 has been calculated for this curve for the different values of 



-^t=/a, and is subjoined, the variation in the value of v being 



neglected, and the boss taken to be of such a radius that co=$2 

 at its surface. This would give, for the lower values of /* a 

 smaller, and for the larger ones a larger boss than that taken in 

 the other table, otherwise the comparison is exact with the line 



in it m which A=2, A being the value of -=■ 



The formula for the H.P. 

 is in this case much more 

 troublesome being 

 </> 2 $2 2 





Horse 

 Power. 



Correspond- 

 ing H.P. in 

 other Table. 



0-02 



114 



102-8 



o-c-3 



176 



I59'3 



0*04 



240 



219- 



0-05 



3°5 



281-6 



o-o6 



372 



347 



0*07 



441 



415- 



( 



H.P. 



2 $2(12- 



Cv 



(2$2+<£) 2 



■4) 



+ £ hyp. log. 



$2X 



where C stands for the con- 

 stant factor reducing to 

 horse power, for a ten foot screw, at ten knots. The difference 

 amounts to about 10% in the lower, and 6% in the higher values. 

 It will be observed that throughout this investigation the 

 pitch of the propeller nowhere comes in directly. Indirectly 

 it does, being fixed at any radius by the longitudinal and cir- 

 cumferential velocities of the water, and circumferential speed 

 of the screw, and is easily ascertained graphically or otherwise 

 when these are known. 



