alternative materials and net protection

Types of materials and designs

The first area of activities within the Dollyropefree project is to develop alternative materials which are much less prone to wear and tear and/or biodegradable. Since conventional dolly rope consists of polyethylene threads which are non-biodegradable, the challenge has been to develop alternatives which are either:

  1. Much less prone to wear and tear and/or are biodegradable;
  2. Or are designed in a different way than threads, but in such a way that they also protect the net. Next to this, alternatives preferably need to be comparable in costs and at least as practical and safe to use on board fishing vessels.

This challenge translates into a (re)search and development process that has so far focused on two kinds of alternatives:

  1. Other types of materials that are more environmentally friendly than the currently used polyethylene. This could be either natural and biodegradable materials or materials less prone to wear and tear. These latter type could be materials that are in itself not environmentally friendly, but because they are less likely to end up in sea, a better option than conventional polyethylene;
  2. Alternative designs for net protection in another form than strings but with the same kind of protective properties as strings.

Since the start of the DollyropeFree project in The Netherlands, various ideas have been shared and tested in practice, ranging from old-fashioned solutions to new and innovative ones.

During the last couple of years, tens of different varieties in materials and designs have been tested both in controlled conditions in a tank filled with seawater and out at sea. Most of these materials have never been tested at sea in these kind of circumstances. During this selection process, it has become clear which materials and/or designs work and which don’t.

Tests and results

So far, three types of materials have been tested in various shapes and forms:

  1. Natural based materials such as wood, hemp and leather
  2. Biopolymers (biodegradable under certain conditions) such as PLA, Solanyl and others
  3. Conventional Polymers such as Polyurethane.

The results of the tests so far have been as follows:

  • Natural fibres are too soft and wear away too quickly. These kind of materials don´t seem to offer a reasonable alternative
  • Yak leather prepared in long strips seem to work well. These are currently tested on a larger scale (see below).
  • Biopolymers that are biodegradable in seawater can be prepared in such a way that they can work as an alternative. These are currently tested on a larger scale (see below).
  • The material Polyurethane designed in the shape of strips seems to be the strongest alternative material. Polyurethane in different levels of flexibility has been tested at sea and seem promising as an alternative material.
  • A net protection design that is based on a product that is used in France also seems promising.

Currently, three alternative materials and designs stand out: strips made out of yak leather, in seawater biodegradable plastic threads and the net protection method that is also being used in France. These alternatives are in the process of being further tested by several ships to see how they perform in practice, if used on a large scale.

Next to this, these alternative materials and designs have to live up to certain standards: they have to be more environmentally friendly, comparable to dolly rope from a financial perspective and at least as practical to use on board.

Since the start of the DollyropeFree project in The Netherlands, various ideas have been shared and tested in practice, ranging from old-fashioned solutions to new and innovative ones. Most of these materials have never been tested at sea.

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