Rearing cages in the sea
Modular Rearing Cages :
The modular process is one of the most successful techniques developed for fish-farms. The idea is simple. Polyethylene cubes are linked by connection screws, creating an assembly that is customised, reliable, strong and flexible.
The cubes are made of Lupolen 52612, a high density polyethylene (0.954 gr/cm3) with a very high molecular mass. These characteristics make it both flexible and strong.
The cubes are linked together by screws, which are turned 1/8th of a turn to lock or unlock. The screws have two retention devices to ensure perfect locking.
The connection lugs are particularly strong (approximately 3 tons tensile load). This ensures the farm train of cages can be anchored in complete security.
Of course, the number of anchorages depends on sea conditions and depth. From experience, it seems that one anchorage every ten metres is a satisfactory solution.
Because of its modular structure, the assembly is extremely secure, since if one of the cubes is damaged it does not jeopardise the buoyancy of the whole structure. Finally, the light and flexible cage train makes it highly resistant to storms, because a cork will always float.
The freeboard can be increased by 40 cm by positioning two cubes on top of each other using long connection screws.
The unique floating walkway system provides a stable platform for farm operatives to undertake all routine inspection, maintenance and fish management tasks with ease, even in difficult conditions.
Parapet of the walkway
This parapet is the heart of this system. The unique design allows the positioning of handrail stanchions for net hanging and the shock absorption unit, which works in tandem with the cage's flexible internal chain, which eliminates wear in the system. This allows the components to flex and return to a stable condition after large wave hits.
Assembly of the modular system is easily accomplished by a small team requiring only a minimum of tools and no welding or lifting equipment (a particular advantage at isolated sites). This means that users can extend their installations with no disruption of their everyday operations and thus achieve enormous advantages in cost and time saving.
This very specific floating footbridge system gives great stability to the footbridge and easily permits, even in extreme conditions, all inspection operations to be underken, maintenance and management of the tasks linked to fish rearing.
Developed in Norway, this process allows a bending of a tortion of the units, due to their junction being mounted on "cylinblocs", to be fixed onto the main surface. The structure is modulable, by the simple addition of plates. It is resistant to corrosion and is comfortable for working due to the breadth of the platform which allows easy management of the cages.
Surface floating cages
Specially devised for exposed sites, these cages offer the following characteristics:
- mechanical resistance (they can withstand waves of 6m in height, currents and violent winds)
- easy to handle
- safe for the users
- long life and low maintenance costs
- the set-up is totally composed of non oxidising material, PEHD.
It is made from a high density polythene tube with an outer diameter of 250mm, thickness 12mm.
The floating circle is composed of tubes with diameters of 250 m, filled with expanded polystyrene foam, supported by one-piece moulded stands, also made from high density polythene.
Each stand is provided with:
1) Two fixing hooks for the nets (very much appreciated especially during changes and reduction of the nets).
2) Two lateral rings maintain a constant gap between the stands with the help of a Nylon cord (very easy mounting).
3) One ring situated on the top of the stand for fixing an anti-bird net.
4) Two specially oversized reinforcements give the stands an excellent resistance.
5) Anti-slip grooves have also been planned on the top of the stand.
The guard-rail which is also supported by the stands is in PEHD.It is white in colour to avoid arm burns during manipulation (very much appreciated in hot regions).
Polyfusion is the technique employed for the assemblage of the tube (the only technique approved for gas pipes under pressure).
It exists in dimensions between 12 and 30m diameter.
A footbridge can be adapted and provides its users with a stable and very safe working surface.
The holding at sea of this type of cage, associated with appropriate anchoring, makes it an ideal tool to perform aquaculture in exposed sites.
They are specially planned for sheltered and semi-sheltered sites.
These cages make it possible to construct farms with wide working footbridges.
Their structure is in AG4 aluminium with a joining cylindrical bloc of very high resistance. Floating is ensured by cellular floats divided into cylindrical shapes. This type of construction allows the manufacture of cages and structures of all sizes.
These cages are made from floating pontoons as used in marinas. The pontoons are in aluminium, set on high density polythene floats filled with polyurethane foam resulting in good resistance to shock, a true impermeability and insubmersibilty.
However, it is preferable that lines of such cages are installed in calm zones. The interest in this system lies in the fact that it is easy to work on the pontoon to carry out tasks such as changing a pocket, sorting etc....
Only few companies share the international market. On the picture, there are PORALU floating pontoons with the following specifications :
MODULES : Length : 6 or 12 m
Width : 1.5 m, 2 m, 2.5 m, or 3 m
Free Board : 0.4 m, 0.5 m, or 0.6 m
Overload : 120 to 250 kg/m
Weight : 6 x 2 element = 500 kg
Link : Stainless steel axis or silent-blocks.Side rails for all fixing.
Frame : Marine Aluminium (6005 T5.3)
Float : Polyethylene + polyurethane foam, very robust, no electrolysis, good fixing, numerous floats.
Gratings : in Polypropylene. Anti-UV treatment, anti-skidding, no maintenance ; Washable with a K‰rcher, anti-bacterial. No screw, no splinters.
10 Years guarantee
Many international companies in the 1980's were interested in aquaculture and huge projects came from design offices. Some of these materialised, others, which were unattainable, were discarded. A honeycomb type barge composed of seven cages was constructed in Spain. Many barges left the construction site and formed thestrating point for industrial aquaculture.
Ce système est prévu pour résister à des vagues de plus de 7 mètres et des courants de 1,75 m/s.
L’intérêt de ce système est le fait que les filets soit maintenus en haut et en bas sur des piliers flottants et lestés. Cela évite la déformation des cages par fort courant et ainsi il n’y a pas de perte de volume. Les piliers sont fixés par des aussières (poulies d’articulation).
Ces structures laissent peu de prise au vent et à la vague. Une embarcation est nécessaire à la gestion; l’avantage majeur est la possibilité d’avoir despoches de grand volume.
Le système d’ancrage, de lest et d’aussières est trés évolué. Toutefois, le coût de telles installations reste très important.
La cage offshore, autre système de très grande résistance, peut subir les assauts d’une mer très agitée, sur le principe de l’iceberg. Une tourelle de maintenance est au sommet de douze flotteurs placés en hexagone. Une rampe d’accès sur flotteurs permet le débarquement et la gestion de la cage. Pour les cages de très gros volume, les filets sont anti-prédateurs.
* Flexible and robust steel cage concept
* Better control of the fish
* The catamaran principle provides good throughflow and makes the installation self-cleaning
* Tasks are easier and more efficient
* Each section (of 2 cages) floats stably and can be easily connected to (or disconnected from) an installation
* Wide pontons and double pontoons as standard.
Cage size : 20 x 20 m, 24 x 24 m and 25 x 25 m, or to customer specification
Freeboard : About 1m
Hinging : Two x two cages
Max wave height : 6 m (3 m significant)
Centre walkway : 4 m wide. Max 8 tonnes point load
Side walkway : 0.8 m wide. Max 6 tonnes point load.
Pontoons : 2 m wide. Max 6 tonnes point load
The catamaran cage comprises two cages combined to make one section. Several sections can be hinged together, so that an installation can comprise 2, 4, 6 or more cages. Each section floats freely, making connection / disconnection of the whole installation a simple operation.
The central walkway : is 4 meters wide and provides a good working platform. Sections are hinged at deck level on the sides of the pontoons with a double hinge at the end of each side walkway and one at the centre walkway.
The centre walkway can carry a load of 8 tonnes in the
In principle the side walkways are designed as pontoons and can take a load of six tons in the middle. They are otherwise constructed so that well boats can lay alongside.
The pontoons in each section are tied together by two side walkways and a centre walkway which spans between the pontoons and extends over the sea. Only the pontoons are submerged. They are designed as a longitudinally-framed hull with a rectangular cross-section. The ribs are supported by transverse frames and water-tight bulkheads. Pontoon strength is so high that one can be held by a single point at each end or by a point in the middle. This allows installations to be located in exposed areas.
The hinges are designed to cope with tensile forces up to 100 tonnes. These maintenance-friendly units have replaceable bronze bushings and easily-accessible lubricant nipples.
Designed to take the weight of the nets, the railings are removable. Attachment points on the walkways are reinforced with double bracket plates.
Corniche du Bois Sacré
83500 La Seyne sur Mer
Tél. : 04 94 10 26 26
Fax : 04 94 10 26 30