PROCEDURES 



Towing performance was exmained at nominal wetted towcable lengths of 850, 250, 

 and 115 m. At each towcable length, the depressor was towed at various set depths 

 to examine the towing behavior corresponding to different depressor lift conditions 

 (flap angle positions). Towing performance was examined primarily at a ship speed of 

 10 knots although some data were obtained at speeds of 5 and 8 knots also. The de- 

 pressor was towed with and without cyclic depth control. Oscillator frequencies 

 less than 0.015 Hz were used during most of the profiling runs since the lower 

 frequencies presumably are of primary interest. However, the depressor response 

 also was examined at an oscillator frequency of 0.2 Hz during one run. 



Streaming and recovery operations were performed at a ship speed of approxi- 

 mately 3 knots to maintain towcable tension at a low value. This was necessary to 

 prevent the top layer of cable on the winch from burying itself under subsequent 

 layers since the cable had initially been wrapped on the winch with no back tension. 



RESULTS 



Seas increased from a state 2 at the beginning of the evaluation to a state 3 

 or 4 during the latter portions. The results of the evaluation are summarized in 

 Table 3. Flap angle, depth, and tension traces from representative profiling runs 

 are shown in Figures 12 through 15. 



During all runs, measured depth deviated substantially from set depth. The 

 discrepancy varied from a maximum of approximately 30 m at a set depth of 200 m to 

 10 m at a set depth of 50 m. Part of the error can be explained by the design of 

 the control system. By design, depth error is zero only at a control-flap deflection 

 of zero; at other flap angles, the error is equal to the flap deflection divided by 

 the flap gain value. This effect, however, accounts for only about 3 m of error. 

 No explanation is provided for the remainder of the discrepancy other than inadequate 

 calibration. Ultimately, depressor depth will be determined using the CTD elec- 

 tronics. Therefore, any depth errors associated with the control electronics are 

 of little concern. 



The ability of the depressor to maintain a constant depth is indicated in Table 

 3 and also in some of the traces of Figures 12 through 14. Generally, as long as 

 the control flap was not fully deflected (as it was during Runs 9 and 10) , the de- 

 pressor maintained a constant depth to within + 300 mm. The control flap response 



26 



