The kinetic deformation of tuna purse seine: A model experiment on different shooting patterns at uniform current

• The effect of shooting direction relative to current direction on the motion and transformation of purse seine was estimated.
• We developed an error calibration algorithm to eliminate the effect of parallax in the processing of image.
• Our results can provide available reference for actual fishing operations.

Vessel position and shooting direction relative to current direction can potentially affect the movement and spatial geometry of purse seine during fishing operations. This study developed an image measurement algorithm to obtain kinetic transformation of a model net when setting in different patterns (shooting with current, front set in shorthand; shooting against current, back set; and shooting lateral to current, cross set) in a specialized purse seine test tank. The results showed some differences in the pattern of deformation in the leadline and floatline. Front set produced the greatest encircled volume by minimizing the area contraction with the open area for floatline in real operation of 0.259 km2 in cross set, 0.266 km2 in front set, and 0.257 km2 in back set, respectively. Different sinking curves were observed in the vertical configuration of middle part of leadline among shooting patterns. Back set is considered as the optimal strategy of setting the net judged from the sinking behavior, as it provides the greatest sinking depth in the middle part of the net. The seiner moved the greatest distance downstream in back set, while the greatest drifting distance inward the circle occurred in front set where it is likely to lead to the seiner drifting over the net. Purse line tension increased continuously until the conclusion of pursing and the bunt was subjected to greater tension force than that at the wing end.