Submersible Netcages for Offshore Farming
From Netcage Systems
This 'Vineta' cages are developed for industrial farming of various fish species (i.e.: Seabass, Seabream, Grouper, Salmon, Sturgeon etc.) all the year round at exposed open water areas such as seas and oceans. To prevent demage from storm impact and to provide optimum conditions for fish farming, the cage can be submerged. Completed with a painted or galvanized framework with a net chamber enclosed and a feed bunker on it allowing automatic feed supply and farming process supervision. To place the cage vertically, it is equipped with a special system providing its surfacing, submerging and positioning at a depth of 4-40 meter.
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Horizontal positioning of the cage is provided by ...
Horizontal positioning of the cage is provided by the system of anchorage including anchor ties and anchors. Lightness and tracery of the cage are in full accordance with the sea landscape. The cage structure is produced to the 'Rules for Building and Classing Underwater Vehicles, Systems, and Hyperbaric Facilities' and passes control assembling and testing at the manufacturing plant. It will have the certificate of the official 'Maritime Register of Shipping'. The steelwork is marked and packed as packages or in boxes wich can be transported in a standard 40-feet container.
The basic material of the (polygon) framework consists of rod welded tubular low-carbon (grade A) steel elements, connected with each other by flange-bolts. The threedimensional framework forming a regular nonahedron in plan, with three slanting trusses, running from the vertival columns to the geometric centre, closing at the feeder casing. The upper contour is completed with service platforms, passage walkways (500 mm wide) with railings (1.000 mm high) and removable hand-ropes, also to the feed bunker. The walkways and brackets are made of pipes with 120 mm in diameter. The vertical columns (720 mm in diameter, 2.250 mm long) house permanently buoyancy compartments, balancing tanks, and compensation tanks of residual buoyancy resulting from discharge of changing loads. Also sensors that measure depth of submergence, water temperature and underwater acoustic are housed there. The 5.980 mm long horizontal members of the bottom contour are made of pipes with 478 mm in diameter and house the main ballast tanks and compressed air cylinders, 6 of wich are ballast compartments and 3 are compressed air cylinders. Three mooring walls with wooden guard rails are provided for service boat mooring. To provide for safety of work of the attending personnel, the cage is equipped with removable single-row life-lines.
The shape of the whole structure and all seperate sections are adjusted so that the cage experiences minimum rolls and trims at waves and current.
The experience of the underwater system operation has proved that the operation in the water column is the most effective structural measure to porotects structures from corrosion. Hot galvanized coating provides the structure service life of more than 20 years. This coating is reliable, practically excluding restoration and repair.
The system of automatic underwater feed distribution is intended for storage and measured distribution of feed for an autonomous operation of 7-30 days and located at the geometric center of the cage. The system consists of a water tight bunker of 3.000 liter (2 tons feed in average) of cylinder-conical shape (1.412 mm in diameter and 2.890 mm in height) and an automatically feed distributor (with a microprocessor) with a volumetric type dosage of 5 liter each. Compressed air is supplied to the pneumatic device by pipelines from compressed air cylinders, wich are replenished from a service boat, equipped with a compressor. To prevent water penetration into the feeder, its upper part is equipped with a water tight hatch with a rack-and-pinion lock. Inside the feeder the upper part houses selenoid valves, system controller and (24 Volt, 125 Ah) batteries. The system is made of corrosion-proof steel (6-8 mm thickness) and non-ferrous metals.
To submerge and surface the cage it is equipped with ballast compartments. The main ballast tanks are filled by gravity via drain holes equipped with ventilating valves with a remote control pneumatic drive. The balancing tanks are filled via kingston valve. The water from ballast compartments is replaced by compressed air (5-10 kg/cm3), supplied from the service boat compressor (min. 150 l/min). Air to the actuators is supplied through the pipelines made of corrosion-proof steel and rubberized hoses. The process of submerging and surfacing is supervised by the depth sensor, its display being located at the service boat or via water acoustic communication channel from the shore.
The signal buoy consists of cylinders of variable sections, providing a platform for deployment and protection of the control and monitoring complex of the cage. The size and weight characteristics are adjusted to provide survivability in the regime of extreme weather conditions. It can operate afloat at wave (force 8-9) and respective wind speed. It also can freeze in ice (up to 50 cm) to stay for winter. Flexible pipelines and electric cables coming from the signal buoy to the cage and supplying compresses air and providing power supply. Additionaly the buoy includes the antenna for an underwater acoustic control and monitoring system with an operation range of 10 km. Safety is provided by flashing beacons and corner reflectors, also from the feed bunker.
To install the cage at the water area (in a depth of up to 50 m), it is equipped with a special system of anchorage, consisting of anchor ties (i.e. a chain with a variable running mass) and 3 anchors (weighing 3-10 t), providing reliable functioning of the system under weather conditions given. The anchors are not included in the delivery, but are made on site (by the customer according to the drawings given). The anchorage system is designed for each particular site depending on hydro-meteorological conditions and depth of an installation site.
The net chamber with a volume of 1.000 to 2.000 m3 is built from kapron or nylon net. The net chamber is placed within the steel structure at special guy-ropes, running up and down from the platform. The guy ropes are fastened to the feed bunker and the net chamber. To provide for harvesting of fish, the net chamber is equipped with a device, consisting of a rope system and portable hand operated winch, raising the bottom edge to the surface. To remove wastes from the net chamber it is equipped with a special tray device wich is lifted to the surface by the help of winches.
It is possible to position the cage system in a depth range in the water column of 4-40 meter. Afloated the system withstands waves (with personel to force 3) without personnel to force 6 and waves up to 6 meter. Submerged it is resistant to force 9 and respective wind speeds and waves up to 8-9 meter.
The axial diameter is 20,12 meter and the light displacement is 16,2 tons. Total height (including 2.000 m3 net chamber) is 12,1 meter, the minimum draught (at launching) is 0,8 meter and the maximum draught (including 2.000 m3 net chamber) is 8,6 meter.
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