Fishing and Gear Technology

Unit-3 Construction of twines

3.5.Ropes
Ropes are extensively used in the fishing gear construction and operation. They provide the frame work and linear strengthening components in the fabrication of fishing net such as gillnets, trammel nets, seines and trawl nets and constitute main line and buoy lines of large longlines. Fibre materials used are Polyamide (PA), Polyester (PES), Polypropylene (PP), Polyethylene (PE), Polyvinyl alcohol (PVAA), manila, sisal, coir, hemp and steel wire. Continuous filaments, staple fibres, monofilaments, film split fibres and natural fibres and combination of different fibre types are used in construction of ropes.

Construction of ropes
Rope generally consists of three or more strands cabled or braided together, with or without a core, with a finished diameter of not less than 4 mm. Based on construction, ropes are grouped into laid and braided. In the laid rope, fibres are twisted into rope yarn and two more yarns are twisted in the opposite direction to produce folded yarns. Three or four folded yarns are laid in the direction opposite to the twist of folded yarns to produce the laid rope. Three strand constructions is the most commonly used and it is called hawser laid or plain laid rope. Depending on the number of twists per unit length, hard, medium and soft-laid ropes are available. A four folded yarn construction is called shroud-laid rope. Three or more laid ropes are combined by twisting in the opposite direction, to produce cable laid ropes. In the braided construction, the strands are plaited together to produce different types of braided ropes. Ropes are specified by material, nominal diameter and construction.

Fibre ropes
Fibre ropes used in fisheries are manufactured from natural fibres such as manila, sisal and hemp and synthetic fibres such as polyamide (PA), polyester (PES), polypropylene (PP), polyethylene (PE) and polyvinyl alcohol (PVAA). Continuous filaments, staple fibres, monofilaments, film split fibres are used for manufacture of fibre ropes. Fibre ropes are widely used for framing and strengthening of fishing gears and also as warps, bridles and sweeps in small-scale trawling operations. Fibre ropes are vulnerable to stretch under sustained strain. Natural fibre ropes are mostly substituted by synthetic ropes, due to their superior rot resistance, long service life and high breaking strength. Considering ropes of same nominal diameter, polyamide (PA) rope has the maximum breaking strength, followed by polyester(PES), polypropylene(PP), polyethylene (PE), polyvinyl alcohol (PVAA) and natural fibre ropes.

Construction of fibre rope
Single fibres are twisted to form rope yarn. Two are more rope yarns are twisted to form folded yarns. Two or more folded yarns are twisted to form fibre rope. Construction of synthetic ropes – Here, the rope yarns may be single yarns or folded yarns and two or more folded yarns are twisted to form cabled yarns. Two or more cabled yarns are twisted to form cable netting yarns. Two or more of these cable netting yarn are twisted to form synthetic rope.

Knotless webbing
Japanese twisting technique
Raschel technique
Braiding technique

Advantages and Disadvantages of knotless webbing and knotted webbings are same. But knotted netting has some principle disadvantage. (1) Knot decrease in breaking strength (2) knots are protruded and abrasion is more. (3) Substantial % of twine is consumed for knots (4) The increase of weight (5) Hydrodynamic resistance is increased
As dirt does not adhere so much to knotless netting it is easy to clean and dry.