TM No„ 377 



5. The off -angle calibrations indicate that two orthogonally mounted 

 meters can detect flow (in the plane determined by the axes of the impellers) 

 to within 10=12 percent of the true velocity. The error,, which is positive, 

 can be corrected by using an empirically determined relationship in which 

 the error is a function of the angle subtended by the current vector and the 

 cylinder axis. This error relationship is independent of the absolute speed 

 of the current . 



There are, however, complex interactions between wave meters and ocean 

 wave motions which can be better judged on the basis of actual wave measure- 

 ments . It was therefore necessary to obtain and examine actual field data 

 in order to provide a real test of the instrument. The orthogonally mounted 

 ducted meter systems (OMDUM II and III) and the collinearly mounted system 

 (COMDUM I) were used extensively on the Buzzards Bay Entrance Light Station. 

 They were suspended at various depths beneath the waves by a system of 

 counterweights and guy wires. This provided a highly lamped suspension, 

 which showed little.; if any, reaction to the horizontal drag inducted by 

 the oscillatory action of the waves. Since the exact method of suspen- 

 sions of the instruments varied with the particular series of measurements, 

 a complete description of the mounting procedures for the various experi- 

 ments is given in chapter IV in the discussion of the field measurements. 



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