by Elihai Radzinski, Fibras Industriales SA, Peru

 

In past articles we have discussed alternative products that FISA produces for the aquaculture industry and how each product can better adapt to different customer's needs depending on the species of fish farmed, the oceanographic conditions, potential predator risks and never to forget the working conditions and maintenance system each specific farm utilises for its cages.

We have already discussed the various ropes that can be used for the structure of the cages and mentioned such options as Polysteel, PE, PP, Nylon, Polyester and FISA's trademark products such as Polymax® and Polytar® ropes.

Additionally, we have discussed the various raw materials that can be used for netting. We mentioned some advantages and disadvantages of nylon netting versus polyester netting, the lightweight advantages of UHMWPE and some potential disadvantages of that product and we finished off mentioning FISA's Supra® Advanced Fibers which is a third generation HDPE netting.

In the following paragraphs we will outline some basic characteristics of the knotted netting, braided netting, raschel netting and Shogun® netting, otherwise known as twisted knotless Muketsu netting.

Raschel 'knotless' netting is probably the most common type of netting used in aquaculture. This knotless netting is a low cost knitting manufactured on Raschel-type machines, thus the origin of the name, and is characterised by the relatively fast production process. Raschel netting is normally manufactured using nylon, polyester, polyethylene or multifilament PP.

A big advantage of Raschel netting is the fact that the nature of the knitting leads to lineal ruptures thus making it much easier to repair. Also, some farmers claim that knotted (twisted or braided) netting can damage the fish skin when it rubs with the knots. We are not sure how to dimension this potential risk in knotted netting, but it must be mentioned.

The biggest advantage of Raschel netting is its price. Because of the fast production process, it is possible to sell each kilogram of netting at much more competitive pricing. Additionally, as the Raschel machines allow for production of wider sections (large numbers of mesh deep) this can lead to less joints requires in the assembling/rigging of the cages thus further reducing costs.

Having mentioned all the advantages of the most common netting, we feel obliged to also mention some potential disadvantages, the biggest one being that this netting is knitted meaning that once there is a small tear it will rapidly extend and increase escape probability.

An additional disadvantage for nylon and polyester Raschel netting, which are by far more resistant than the polyethylene or pp versions of this netting, is the fact that these are multifilament products and the looseness of the filaments means there will be higher probability of fouling attaching to the netting at a faster pace.

As always, the specific natural conditions and working habits of each farm will determine whether Raschel netting, and what raw material, would be most adequate for that farm. FISA's vast experience with producing Raschel netting for over 50 years in all its variations can be critical to defining the most effective and cost-efficient version to be used.

A second type of netting FISA has been manufacturing for over 70 years is the twisted knotted netting. This netting is mostly manufactured using nylon, polyester or polyethylene and has the advantage that the material is twisted together in three strands thus reducing the speed at which fouling attaches to the material. The twisting of the material creates a much more stable and solid structure and the knots prevent any ruptured sections from spreading and turning to larger holes in the cage or predator netting.

The main disadvantages of twisted knotted netting are the fact that the knots increase the weight of the cage and are also critical points of potential increased friction/abrasion during manipulation of the cages or under the effect of strong currents.

The third type of netting we will explore is the braided knotted netting. This netting is manufactured on similar machines as the twisted knotted netting but instead of using three strand twisted material, the netting is woven of 16 strand braided nylon, polyester or HDPE.

The fact that the material is braided as opposed to twisted adds flexibility to the netting and this is especially advantageous in products such as FISA's Supra® Advanced Fibers that are made of third generation HDPE and by nature are less flexible.

An additional advantage of the braided netting when compared to twisted knotted or Raschel netting is its stronger resistance to the effects of abrasion while maintaining an advantage of less fouling impregnation.

Last but not least we will mention twisted knotless Shogun® netting which is known in Japan as Muketsu netting. This netting is manufactured with high tech machinery developed in Japan and available only to a limited number of leading netting manufacturers.

The Shogun®/Muketsu Twisted knotless netting is composed of two strands of twisted twine with each strand running through the other thus creating seamless meshes with no knots between them. This production process sounds a little confusing but if you look at a picture, or better yet at a sample, of this netting you can immediately notice the vast difference with all other type of netting.

Shogun®/Muketsu twisted knotless netting can be made using nylon, polyester or polyethylene and its main advantage is the very strong breaking load that can be reached with extremely low weight of netting.

The fact that this netting has no knots avoids the potential damage to the fish when rubbing with the netting and facilitates all maneuverability and cleaning process.

If we analyse the use of Shogun®/Muketsu twisted knotless netting specifically for bird protection, we can identify a very important advantage in the fact that this netting permits for stronger tension when spreading the net and the low weight together with good tension upon installing reduces the risk of potential curvatures that the birds always identify as the weakest link and use in order to reach their tasty meals.

A few years back FISA developed Polyethylene Shogun®/Muketsu twisted knotless netting specially designed for bird nets as this product is extremely resistant to abrasion and to UV rays. This product, though relatively more expensive, has been extremely well received by many customers who clearly identified the advantages and durability of the product.

Over the past few months FISA has started developing Shogun®/Muketsu twisted knotless netting using its Third Generation HDPE known as Supra® Advanced Fibers. It is with this material, we believe, that FISA will be able to maintain its global leadership and innovation, thus allowing its customers to constantly benefit from our extended experience and technical knowhow.

It is important to finish off by reiterating that every single farm has specific natural conditions and working habits and there is no 'best type of netting' that suits all.

FISA's vast experience in the fishing, aquaculture, security and sports netting markets together with our one stop shop as manufacturers of all the types of netting is what allows us to tailor suit the adequate product for each farm and usage. We currently supply rigged cages to all five continents for usage in offshore, inshore and lakes and will be glad to recommend the most adequate products for any existing or future development projects.

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