166 VARIATIONS OF SHAFT HORSE-POWER, ETC., 



In Fig. 4, Plate 99, are shown the actual observations of the torque and thrust 

 pen deflections, and the revolutions per minute of the propeller shaft plotted on speed 

 of the model, the latter being measured by the speed of the towing carriage in the 

 same manner as in the ordinary resistance tests. 



The following are the dimensions of the propeller used in the experiments and 

 also the dimensions expanded to the ship scale : — 



Model Ship 



Diameter 10.125" 16' 7" 



Pitch 9.0" 14' 9" 



Pitch ratio 0.889 



Mean width ratio » 0.20 



Number of blades 3 



Ratio of projected to disc area 0.266 



Blade thickness fraction 0.04 



The propeller had three blades of Taylor's standard form. 



The propeller characteristics were obtained by separate tests of the propeller 

 model run in free water, that is, in a separate apparatus where the propeller shaft 

 projected well ahead, so that the propeller ran in water undisturbed by the action 

 of the testing apparatus. The same motor dynamometer was used for the tests as 

 was used for the self-propulsion tests, the only difference being that the propeller 

 shaft was coupled to the forward end of the armature shaft instead of the after end. 



The characteristics of the propeller are given in Fig. 5, Plate 100. The thrust 

 constant, Cj., and the torque constant, Cg, are plotted on nominal slip following the 

 method used by Schaffran.* These constants, which are in non-dimensional form, 

 lend themselves well to the analysis of self-propulsion experiments and to the ex- 

 tension of the results to the full-size ship. 



The results of the investigation are given in Figs 6, 7, and 8, Plates loi to 103. 

 An examination of the effective horse-power curves and the shaft horse-power 

 curves for the different models shows, as would be expected, a wide variation in 

 power required. By plotting cross curves of power at a speed of 11 knots it will 

 be found that, for both the effective horse-power and the shaft horse-power, the 

 best results are obtained when the middle section of the parallel middle body is 

 placed about 43 per cent of the ship's length from the forward perpendicular. But 

 2,000 shaft horse-power is required for the ship represented by model 2,133 ^.t a 

 speed of II knots. This is considerably b^low that obtained with the ordinary 400- 

 foot cargo ship of this displacement and may possibly be questioned as to whether it 

 is not lower than could be expected to be obtained on a real ship. It must be remem- 

 bered, however, that the lines are of good form and the friction of the shaft has 

 been eliminated, so that the powers given do not include shaft friction. As to the 



*"Systematische Propellerversuche ;" K. Schaffran, Schiflfbau, September 22, 1915. 



