Design and selection criteria
When determining what type of codend will be used aboard your vessel, you should consider many performance criteria, such as:
Codend capacity is determined by the following variables:
To approximate codend volume or capacity, refer to the following table. This table should be used for an approximation only. For example: If a codend has a circumference of 24 feet (7.32 meters) and a length of 65.6 feet (20 meters), the codend capacity would be 72 metric tons.
After the codend’s capacity and size have been determined, the appropriate strength must be designed into the codend to facilitate safe and secure handling. The type and size of netting, riblines, container lines, and other load-bearing components can then be determined. It is also vital to consider other conditions which may stress the codend such as the slope of a vessel’s stern ramp, at-worst weather conditions, and foreign objects that might accidentally be caught.
Netting should be selected with respect to:
Various materials are available to protect codend’s from abrasion caused by the seabed, stern ramps, and fish. Typically, NET Systems codends are partially enclosed in a protective netting layer made of a larger mesh size than the primary fish-holding layer, thus enabling juvenile or non-marketable species to escape. This “sacrificial layer” may also be covered with an additional protective layer of stranded polyethylene material commonly known as hula skirt or chaffing rope.
Other areas that may require protection include:
Maximizing the flow of water and fish into the codend is a priority to maintain fish-catching efficiency. Several methods may be applied to assure this:
Because large codends tend to be of rather heavy construction, proper flotation is critical to maintain a clear opening for the entrance of fish. A few guideline to achieve this include:
Many options are available for hauling and handling codends. All techniques should be sized to allow for a sufficient, safe working load margin to ensure safety and security while lifting. Maintaining a lightweight handling system also helps. Many types and styles of lifting rigging are available, including:
In today’s high-technology and competitive fisheries there is frequently a need to design codends that target a particular size and/or species of fish. Netting mesh size or configuration can be applied in order to accomplish this task. Some available options include:
Many of the world’s fisheries operate under government regulations specifying a minimum mesh size. In most cases these laws apply to the inside opening of the mesh or a between-knots (BK) measure. Frequently, as a result of extended use and wear, netting may stretch or shrink, resulting in possible violation of the regulation. In such fisheries, one should consider: