12 



RESISTANCE OF BILGE KEELS. 



Plate 1 6 represents the observations of input to the electric motor in kilowatts 

 on the dates of July 28 and August 12, black points referring to the former date 

 and circles to the latter date. Diagrams for the other series of tests are as satisfac- 

 tory and need not be reproduced. From curves like those of Plate 16 have been de- 

 duced the usual curves of power on speed as given on Plate 20. For this purpose 

 the rating of the motor by brake tests in 191 2 are accepted, because the motor and 

 mechanism are in substantially the same condition and any possible change cannot 

 sensibly affect the increments in power due to adding bilge keels. 



Having offered sample diagrams and claimed for them the degree of precision 

 demanded for the work in hand, it is proper to account for the dispersion of points 

 on Plate 14 and to justify the application of the curve of Plate 15 even when the ob- 

 served points show deviation from it. 



The experience of former years having shown the ill effect of a breeze, only 

 favorable weather conditions were accepted this season, with the breeze so light 

 that it had no appreciable effect. Nevertheless there was an appreciable deviation 

 of results obtained from runs back and forth over the course. Collation of all the 

 series as in the following table shows that these deviations were caused by currents 

 in the Basin due apparently to winds that had blown before the runs were made. 

 These currents were very feeble and could not be detected by any of the usual 

 methods of measurement, although they persisted eight to twelve hours after the 

 wind ceased blowing. 



Table I. 

 Currents in Charles River Basin Due to Previous Effect of Winds. 



