Experimental samples of knotless nylon (polyacrylamide or PA) netting (left, four-strand braid) and knotted nylon netting (right, single English knot).

<p>Experimental samples of knotless nylon (polyacrylamide or PA) netting (left, four-strand braid) and knotted nylon netting (right, single English knot).</p

Comparison of parallel drag coefficients vs. Reynolds number.

<p>Comparison of parallel drag coefficients vs. Reynolds number.</p

Comparison of normal drag coefficients vs. Reynolds number.

<p>Comparison of normal drag coefficients vs. Reynolds number.</p

Comparison of inclined hydrodynamic coefficients between knotless netting panels and knotted netting panels at various attack angles and flow velocities.

<p>Comparison of inclined hydrodynamic coefficients between knotless netting panels and knotted netting panels at various attack angles and flow velocities.</p

Hydrodynamic characteristics of knotted and knotless purse seine netting panels as determined in a flume tank

<div><p>Nylon (PA) netting is widely used in purse seines and other fishing gears due to its high strength and good sinking performance. However, hydrodynamic properties of nylon netting of different characteristics are poorly understood. This study investigated hydrodynamic characteristics of nylon netting of different knot types and solidity ratios under different attack angles and flow velocities. It was found that the hydrodynamic coefficient of netting panels was related to Reynolds number, solidity ratio, attack angle, knot type and twine construction. The solidity ratio was found to positively correlate with drag coefficient when the netting was normal to the flow (<i>C</i>_<i>D</i>90), but not the case when the netting was parallel to the flow (<i>C</i>_<i>D</i>0). For netting panels inclined to the flow, the inclined drag coefficient had a negative relationship with the solidity ratio for attack angles between 0° and 50°, but a positive relationship for attack angles between 50° and 90°. The lift coefficient increased with the attack angle, reaching the culminating point at an attack angle of 50°, before subsequent decline. We found that the drag generated by knot accounted for 15–25% of total drag, and the knotted netting with higher solidity ratio exhibited a greater <i>C</i>_<i>D</i>0, but it was not the case for the knotless netting. Compared to knotless polyethylene (PE) netting, the drag coefficients of knotless PA netting were dominant at higher Reynolds number (Re>2200).</p></div

Drag coefficient for netting parallel to the flow as a function of Reynolds number for various solidity ratios.

<p>Drag coefficient for netting parallel to the flow as a function of Reynolds number for various solidity ratios.</p

Comparison of drag coefficient of inclined nylon netting panels with varied solidity ratios against attack angle.

<p>Comparison of drag coefficient of inclined nylon netting panels with varied solidity ratios against attack angle.</p

Comparison of drag coefficients between knotless nylon (PA) netting and knotless polyethylene (PE) netting.

<p>Comparison of drag coefficients between knotless nylon (PA) netting and knotless polyethylene (PE) netting.</p

Relationship between hydrodynamic coefficients of netting panels and attack angles: Drag coefficient (left), lift coefficients (right).

<p>Relationship between hydrodynamic coefficients of netting panels and attack angles: Drag coefficient (left), lift coefficients (right).</p

The ratio of frame drag to total drag under different flow velocities.

<p>The ratio of frame drag to total drag under different flow velocities.</p