34 



Fishery Bulletin 104(1) 



then determined by integrating Equation 4 from Xi„,^.^,^ 

 to the value of .v at which S=L. The wing tip to wing 

 tip distance IJ,,,,,,^,,^ is then calculated as 



1 



D. 



•ingtip 



-yio 



,)^+(a:„ 



(5) 



where .v,,^^^. and yi„,^,^,, are obtained from Equation 1. In 

 the second stage, c is varied and the above process is 

 repeated iteratively until the value of O,, ,„„„^j is found 

 that is closest to the measured net spread. At this point 

 the calculated values of Z),,,„„„^, and the tangent at the 

 headrope center will equal the measured values. 



The headrope-shape model for each offset was used 

 to project the off-bottom distances measured at the five 

 positions along the footrope onto a plane orientated 

 perpendicular to the direction of travel to depict the 



shape of the footrope as it would appear from a position 

 in front of the trawl. To do this, a shape function was 

 developed for the footrope. Assuming that the coordi- 

 nates of the endpoints of the footrope (-v,,,,, ^,^, -v^^,^^,,^, >'/o„,pr' 

 y ^) were the same as the headrope. Equation 5 was 

 iteratively integrated with varying values of c until the 

 estimated value of the footrope length (S) equaled the 

 true length (34.1 m): 



S= \ [l + (2cx)-)' dx. 



(6) 



Once c is determined, Equation 4 is integrated to find 

 the value of .r associated with the value of S at each BCS 

 (bottom current sensor) position on the footrope. 



