The change in physical properties of some nylon (PA) netting samples before and after use

This experiment investigated the differences in breaking load and elongation obtained applying the International Organization for Standardisation (ISO) 1806–2002 standard to knotless netting before and after use. The knotless netting samples we measured are representative of the netting used at present by the Italian fishing net factories. In particular, this netting is made from the thicker and stiffer twines used commercially in the manufacture of Italian bottom trawls. In order to simulate used netting, a loading and unloading treatment has been applied to new knotless netting. Before the laboratory test, we investigated how many samples are necessary to detect the differences between treatments with acceptably high power. The principal significant differences were observed in elongation, while none was detected in breaking strength. In knotless netting samples after use, the elongation reduced. The extensibility performance of netting material is very important especially if the meshes are desired to have constant length, for instance, there in the body of bottom trawls. It is advisable to stretch new meshes to remove the irreversible part of the elongation before the netting is fitted to a trawl. For definite conclusions, the netting performance has to be monitored over extended periods of actual work. This suggests that the International Organization for Standardisation should prepare an additional test standard or modification to the ISO 1806–2002.