98 



NATURAL SCIENCE 



[August 



In order to determine the efficiency of propulsion it is only 

 necessary to find what proportion of the whole work done is 

 developed as kinetic energy in the water. If the whole pressure 

 of the blade against the water be P, while the centre of pressure 

 moves through a distance a perpendicular to the blade, the kinetic 

 energy delivered to the water is Pa. For every small angle 6 through 

 which the blade turns while the turning point is at a distance x 

 from the centre of pressure, the above product *= PxO. 



Without entering into details, 1 the angles between successive 

 positions of the oar, given in Fig. 6, were measured and corrected 

 by interpolation from a curve, while corresponding values of x and 

 P were found from Fig. 9 and C of Fig. 4 respectively. 2 



In this way it was found that almost exactly £ (33'4 per cent.) 

 of the work was left behind in the water as kinetic energy set up 

 by the oar, giving an efficiency of 66*6 per cent. This efficiency 

 coefficient is concerned, of course, only with the rowing mechanism, 

 and takes no account of physiological waste of energy. 



Fig. 10. 



Fatigue Effect. 



A, Work ; B, Greatest Pull ; C, Change in Form. 



The mechanical efficiency is increased by increasing the size of 

 the blade, so that it can react on a larger body of water, and by in- 

 creasing the length of the oar, both inboard and outboard, in order 

 to diminish the obliquity at the ends of the stroke. This theoretical 

 possibility is hampered by practical considerations until boatbuilders 



1 See Appendix II. 



2 C unfortunately was not the oarsman who was rowing in the oar experiment, but, 

 for a general result, this is of no very great moment. 



