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 In recent years, the tendency
in some sectors of the fishing industry has been to use thicker and stiffer twines
in the manufacture of netting material. This increases the mesh’s resistance to
opening and, consequently, reduces the selective performance of fishing gears. The
main characteristic of netting twine contributing to mesh resistance to opening
is flexural rigidity (EI). The Fishing Technology Unit (FTU) developed a methodology
for quantifying mesh resistance to opening through
the use of a prototype called
the resistance to opening and deflection meter (ROD-m). It incorporates four tension
load cells and four stepping motors that are driven by four ministep bipolar chopper
drives. Moreover certain section of the textile net factories have begun to manufacture
new knotless netting in nylon, which is an important component of many fishing gears.
Nevertheless, many of their mechanical characteristics, and the factors which influence them, have not been sufficiently investigated. FTU is able to investigate and measure
the physical properties, such as tensile strength and extensibility on special testing
instruments. some International Organization for Standardisation (ISO) recommendations
(ISO 1805–1973, 1806–2002, 2307–1990) established standard specifications for the
methods of testing, the selection and the conditioning of the netting samples for
test, the procedure of testing, the testing apparatus and the evaluation and presentation of the results of the tests. However, frequently only new, unused netting materials
are tested under standard testing conditions. Although such information is essential
for the evaluation and selection of netting materials, it is not enough for a conclusive
judgement of the performance of netting under actual working conditions. Important
properties, such as breaking strength and elongation can change considerably under
varying loading stress, type of usage and duration of use. By complementary laboratory
tests, certain basic working conditions such as sustained loading, repeated loading,
shock loading, abrasion, etc, can be simulated and the results of the tests improve the possibilities for deducing the likely suitability under real working conditions.
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