Codend and Brailers

Codend and Brailers

Design and selection criteria

When determining what type of codend will be used aboard your vessel, you should consider many performance criteria, such as:

  • Volume/Capacity
  • Strength
  • Netting type, configuration, and number of layers
  • Protection from abrasion
  • Water and fish movement through the system
  • Flotation
  • The vessels’ hauling ability and deck capacity
  • Required handling rigging and hardware
  • Fish size selectivity
  • Fishery Regulations

Volume and Capacity

Codend capacity is determined by the following variables:

  • Length and circumference
  • Density-the specific gravity of species harvested and how tightly they pack
  • Length of time fish are in the codend and the resulting compression

Codend Capacity Chart

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.

Codend Capacity

(metric tons)

Circumference
(ft/m)
Length (ft/m)
16/5 33/10 49/15 66/20 82/25 98/30 115/35 131/40
30/9.1 28 56 85 113 141 169 197 226
28/8.5 25 49 74 98 123 147 172 197
26/7.9 21 42 64 85 106 127 148 169
24/7.3 18 36 54 72 90 108 126 144
22/6.7 15 30 45 61 76 91 106 121
20/6.1 13 25 38 50 63 75 88 100
18/5.5 10 20 30 41 51 61 71 81
16/4.9 8 16 24 32 40 48 56 64
14/4.3 6 12 18 25 31 37 43 49
12/3.7 5 9 14 18 23 27 32 36
10/3.1 3 6 9 13 16 19 22 25

Strength

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 Type

Netting should be selected with respect to:

  • Inside measure of the mesh opening
  • Twine diameter
  • Type of material (polyethylene, nylon, Dyneema┬«, etc.)
  • Single or multiple layers
  • Type of netting (Ultra Cross┬« knotless, Twisted Cross, knotted, etc.)

Protection from Abrasion

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:

  • Portions of the codend beneath chokers and straps
  • Hangings and lashings that may contact the seabed
  • Portions of the codend susceptible to repeated abrasion during handling

Water and Fish Movement Through the Codend

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:

  • Construction with a single layer of netting
  • Use of Ultra Cross netting especially UC Silver netting using fiber to make the strongest and lightest netting possible
  • Use of a codend with the largest circumference possible
  • Maintaining open meshes throughout the intermediate and codend
  • Avoiding restriction around the girth of the codend
  • Proper floatation
  • Consistent circumference between the end of the trawl, intermediate, and codend
  • Minimizing chafing gear resistance to water flow
  • Use of lightweight chokers and lifting bridles

Floatation

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:

  • Provide sufficient flotation to achieve at least neutral buoyancy
  • Install all floats in the upper portion to prevent twisting
  • Install all flotation inside the codend to prevent damage and loss
  • Use the largest floats possible for cost savings and simplicity

Handling Rigging and Hardware

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:

  • Chokers made from wire rope, synthetic rope, and Dyneema® rope – high-strength rope made with Dyneema® fiber
  • Four-way lifting bridles made from similar materials that do not choke or abrade the codend
  • Specially designed systems to suit your particular requirement

Fish Species and Size Selectivity

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:

  • Interchangeable top panels of various mesh sizes, which may be easily changed to suit the fishing condition
  • The square mesh netting configuration (bars of netting run parallel and perpendicular to gores/riblines). Square mesh maintains a consistent and square opening regardless of loading condition. It also assures maximum circumference while towing. Ultra Cross netting is the premier netting for this application, as netting distortion is virtually impossible
  • High-strength/low-stretch riblines may be hung to the codend shorter than the netting length to maintain open netting meshes

Special Local Codend Regulations

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:

  • Using a netting with minimal elongation characteristics, such as Ultra Cross
  • Using netting that has been well depth-stretched, or Ultra Cross, to avoid knot slippage or distortion
  • Ordering netting with a safety margin slightly greater than the stated legal mesh size
  • Being knowledgeable about the regulation and periodically inspecting the netting during use