Anchoring analysis of deep water wind-wave resistant net cage

Deep water wind-wave resistant net cage mostly use high-density polyethylene (HDPE), HDPE pipe has light weight (specific gravity 0.95), good toughness, good tensile and bending performance etc., and can be undulated with the waves on the sea surface, relieving the direct force of the waves on the net cage, so as to use the physical properties of the material itself to achieve the role of wind and wave resistance. Therefore, HDPE material is generally used, and the specification of the main pipe of the round net cage is Dia. 250mm, wall thickness is 14.8mm, and the net cage is designed to resist wind above 12 levels.

There are two most commonly used anchoring methods for deep-water nets, one is "一" shape, four or five cages in a group, and the other one is "田" shape, four cages in a group.

A.Anchoring for “一” shape
The advantage of "一" shape anchoring method is that the fixed net cage has great strength, which is good for daily management and easy maintenance; the disadvantage is that it takes more materials for fixing, and the whole net cage is easy to be deformed by wind and flow, but it does not affect the strength of each group of net cage. The interval of each group of net cage is 30m, fixed by anchors and piles, there will be about 32pcs wooden piles and 12pcs iron anchors, and the anchor ropes of the net cages are made of polyethylene ropes. (The anchoring layout of "一" shape net cage is shown as Pic. |
1.)

Pic.1

B.Anchoring for ”田” shape
The advantage of "田" shape fixing method is that the force around the net cage is uniform, it has good effect to mitigate the impact of wind and waves, and the material is less than "一" shape, but the disadvantage is that it is not favorable to the daily management and maintenance. The anchor piles can also be fixed with iron anchors, and polyethylene ropes are used for the anchor ropes of the net cages. (The anchoring layout of "田" shape net cage is shown as Pic.
2.)

Pic. 2
 

C.Advisories and Precautions
Deep water wind-wave resistant net cage is an intensive aquaculture facility, mainly used for the aquaculture of marine fish in semi-open or open sea area above 15m water depth offshore. According to the sea conditions and aquaculture species, please choose the suitable net cage and anchoring method. In semi-open or open sea conditions, it is recommended to use the rope frame cushioning anchoring method, do not connect the net cage frame without cushioning.

Strengthen daily management, regularly check the safety of cage facilities, eliminate hidden risks in a timely manner, and prevent fish escape. It is recommended to regularly monitor changes in the sea environment, pay attention to weather changes, avoid floating objects at sea, and timely remove net-coat attachments. Strictly control the occurrence of diseases, timely remove sick and dead fish, and should be centralized for harmless treatment. Pay attention to natural disasters and man-made damages to the nets, use Ultra-high Molecular Weight (UHMW-PE) high-strength nets as much as possible to protect the safety of cultured fish.