WO2010098675A1

WO2010098675A1 - Float element

Info

Publication number: WO2010098675A1
Application number: PCT/NO2010/000073
Authority: WO
Inventors: Alf Kristian Fjelldal
Original assignee: Akva Group Asa
Priority date: 2009-02-26
Filing date: 2010-02-25
Publication date: 2010-09-02
Also published as: NO329803B1; NO20090892L

Abstract

There is described a float ring (1) for a fish farm net pen arranged to be able to be arranged in a mass of water (4) the float ring (1) being constituted by one or more elements (1') formed by extrusion of at least one material the specific weight of the at least one material decreasing in a direction from the surface (111) of the element (1') toward the core (112) of the element (1') and an in the working position of the element (1') an upward facing portion of the surface (111) of the element (1') forms a walkway (14). Also described is a method for manufacture of said float ring (1). Also described is a use of said element (1') as a floating walkway.

Description

FLOAT ELEMENT

The invention relates to a float ring for a fish farm net pen, more particularly in that the float ring is constituted by one or more elements formed by extrusion of at least one material, the specific weight of the at least one material diminishes in a direction from the element surface toward the element core, and an in the application position of the element upward directed portion of the element surface forms a walkway. The invention also relates to a method for manufac- turing said floating ring. The invention relates further to use of said element as a floating walkway.

On a fish farm net pen floating means are used secured to an upper portion of the net defining the cage against the adjacent water masses. The floating means are typically shaped as a continuous float ring encircling the net, and are often formed by a tubular plastic material. By arranging two or more float rings concentrically, a stable basis or footing for a walkway and technical equipment being permanently or temporarily arranged in or at the net pen is provided.

To avoid the buoyancy of the float rings being reduced to any extent if the tubular wall is perforated, the inside cavity of the float ring is often filled with a material having good buoyancy properties, such as blocks of expanded polystyrene. One of the drawbacks in using such buoyancy material is that a rupture in the float ring may lead to the buoyancy material drifting away representing both a cost when lost buoyancy material is to be replaced in repair of the float ring and a source of pollution, as material of this kind decomposes slowly in the nature. Moreover buoyancy material of this kind does not provide any structural stability and strength improvement beyond a certain increase in resistance against cross-section deformation. The buoyancy materials do not for example contribute to moorings and other elements achieving a better fastening to the float ring.

To maintain stability and uniform loading on the floating means for a net pen system having several rings, the float rings are interconnected by means of connector elements. These represent among other things a danger for wear and possible rupture in the float ring.

The object of the invention is to remedy or reduce at least one of the prior art drawbacks .

The object is achieved by the features stated in the below description and in the following claims.

The invention relates to a float ring arranged to be able to hold an upper portion of a net pen in a fish farm outstretched in a mass of water. The float ring is provided by extrusion from one or more materials and exhibits a cross- section where the specific weight of the resulting material mix is reduced from the periphery of the cross-section and toward one or more core areas in the cross-section. The specific weight typically decreases from the order of 0.9 kg/dm³ at the periphery of the cross-section, i.e. the surface of the float ring, and to the order of 0.2 kg/dm³ at the core. This variation in specific weight is provided during the ex- trusion by the resulting material mix density decreasing toward the cross -section core in that the pore volume of the material mix increases from virtually nothing at the cross - section periphery to a maximum at the core.

The cross-section of the float ring is of a kind providing sufficient width and stability for a walkway at an upward facing portion of the float ring in its application position is possible to form. The extrusion element is given a shape providing a concentration of the float ring buoyancy volume toward the outside and inside periphery of the float ring, while an intervening mid portion shows reduced draught. The width of the cross-section may be increased without the overall height of the float ring exceeding what is desirable based on functional reasons. The walkway may thus be given an adequate width within the extent of the one float ring. The provided shape of the float ring cross-section also increases the float ring resistance to radial deformation and torsion, i.e. the shape of the float ring is maintained to a larger extent than prior art float rings.

The material properties of the at least one selected ex- trudable material provides the possibility for forming re- cesses in the float ring for fastening of adjoining elements such as mooring systems, railings, etc. Drilling, milling or the like may typically form the recesses, and simultaneously with or after forming the recess boundary surface is heat- treated to form a boundary surface having approximately the same density as in said cross -section periphery. Thus the stability of the recess is increased.

By extrusion it is possible to form patterns in the walkway such as longitudinal ridges or grooves. There also exists the possibility of impressing a friction pattern in the walkway by subsequent rolling while the material is still plastically formable. Fusing in of a friction material is also possible. Extrusion also makes possible the forming of ridges defining the walkway toward the float ring surroundings .

To be able to provide float rings having a circular outline, the curved element having a radius of curvature essentially corresponding to the final radius of the float ring is formed.

To simplify transport of the float ring to the fish farm location, the float ring is formed as several curved elements each representing a ring section, such as 1/8 of the float ring. These are joined together at the fish farm location to a continuous ring by such as welding according to prior art.

The element may also be used as a floating walkway such as between shore and a net pen or between boats in a small craft harbour. Forming the elements in straight lengths is then an obvious solution.

In a first aspect the invention relates more specifically to a float ring for a fish farm net pen, characterised in that the float ring is constituted by one or more elements formed by extrusion of at least one material, wherein the specific weight of at least one material decreases in a direction from the surface of the element toward the core of the element, and an upward facing portion of the element in its application position forms a walkway.

The element cross-section may exhibit a mid portion which in the working position of the element exhibits an in the vertical direction smaller draught than the draught of the adjacent side portions in the element cross-section.

The walkway may be provided with raised walkway thresholds. There may be provided a series of friction elements in the walkway.

The friction elements may be formed as ridges in the walkway.

The friction elements may be constituted by mineral particles fastened to the material surface.

The float ring may be provided by a series of elements being rigidly joined together.

In a second aspect the invention relates more particularly to a method for manufacturing of a float ring for a fish farm net pen, characterised in that at least one element is formed by extrusion of at least one material, wherein the specific weight of the at least one material decreases in a direction from the surface of the element and toward the core of the element, as a walkway is formed in an upward facing portion of the surface of the element in its working position; and the float ring is formed by that a first end portion of the at least one element is interconnected with a second end portion.

The element may be formed having a radius of curvature essentially equal to the radius of the float ring.

Friction elements may be formed in the surface of the walkway during extrusion.

The walkway may be provided with a friction coating being provided by a series of mineral particles fastened to the walkway surface .

The mineral particles may be fastened to the walkway surface by use of an adhesive or by forcing the particles into the extruded material . The mineral particles may be heated before being forced into walkway surface .

The friction elements may be machined by rolling.

In a third aspect the invention relates to a more particular use of an element as described above, as a floating walkway.

In the following is described an example of a preferred embodiment illustrated in the accompanying drawings, wherein:

Fig. 1 shows a schematic side view of a fish farm net pen;

Fig. 2 shows in a larger scale a cross-section through a float ring element according to the invention;

Fig. 3 shows in a smaller scale a plan view of a float ring element according to the invention; and

Fig. 4 shows in a smaller scale a plan view of a float ring made up of a series of float ring elements.

In the figures the reference numeral 1 indicates a float ring arranged at a net pen 16 upper portion and floating in a surface of a mass of water 4. The float ring 1 may be made up of several elements 1' which in a suitable way are interconnected to a continuous form stable ring, for example by weld- ing.

A bottom ring 2 is in a per se known way attached to a lower portion of the net pen 16.

A mooring system 3 comprising several mooring lines 31 connecting the float ring 1 to a series of bottom attachments (not shown) is fixed to the float ring.

The element 1' shows a cross -section having two side portions lla, lib and an intermediate mid portion lie. A substantially plane portion extending over substantially the largest extent of the whole cross-section, forms a walkway 14 which in the float ring 1 working position faces away from the masses of water 4. The side portions 11a, lib have larger draughts in the water mass 4 than the mid portion lie.

The element 1' has a sealed surface 111 and two cores 112. The element 1' is formed by extrusion of one or more suitable materials in such a way that the specific weight of the extruded material decreases in a direction from the surface 111 and toward the cores 112. Suitable types of material may be from the group comprising high-density polyethylene (HDPE) , medium density polyethylene (MDPE) and plastic based composite mixtures. The specific weight decreases in a direction from the surface 111 of the element 1' and toward the cores 112 of the element 1' from the order of at least 0.9kg/dm³ and to the order of 0.2kg/dm³ or less.

A recess 12 extends diagonally through the cross-section of the element 1' from the walkway 14 to a portion of the surface 111 which in the working position of the float ring 1 is submerged in the mass of water. The channel 12 has boundary surfaces 121 against the element 1' . In an alternative form the recess 12' extends vertically and only partially into the cross-section of the element 1' . The recess 12, 12' may be formed by drilling, milling or the like for removal of mate- rial from the element 1' and coincident or following heat treatment of the boundary surface 121 to provide a boundary surface 121 with substantially the same material properties as the surface 111 of the element 1' .

The mooring system 3 mooring lines 31 are fixed to the float ring 1 as they are pulled through the corresponding recesses 12 in the element 1' (see figure 2) and secured by a locking means 311. Railing 15 and/or other surface installations (not shown) are fastened directly or indirectly to the float ring 1. In figure 2 is indicated a railing post 151 led toward the corresponding recess 12' for fastening in the element 1 by such as a force fit.

The walkway 14 is defined by upwards extending walkway thresholds 141. The walkway 14 is further provided with a series of friction elements 142, indicated in figures 2 and 3 as ribs extending upwards from the walkway 14 and formed in the same material as the float ring 1 by extrusion and plastic forming. In an alternative embodiment the friction elements may be formed as a coating of mineral particles (not shown) pasted on the surface 111 on the float ring 1 by means of an adhesive or by melting partly into the walkway.

The cross-section of the element 1' can appear in a number of shapes all within the scope of the invention. The essential thing is to obtain an adequate width such that the walkway 14 may be formed as a surface portion of the float ring 1. By placing an essential part of the float ring 1 buoyancy volume near the inner and outer periphery of the float ring 1, the intended stability and carrying capacity is achieved. A cross-section for example shaped approximately like a catamaran, as the walkway 14 is partly constituted by an interconnecting deck between to "hulls" formed as a continuous unit by extrusion may be considered.

The float ring 1 is formed by extrusion according to per se prior art. To provide a float ring 1 with the desired curvature, the extrusion process is controlled so that the element 1' is given a desired radius of curvature corresponding to the radius R of the float ring 1 (see figure 4) . By the very fact that it is impractical to transport a float ring 1 in its final shape, and based on the fact that the element 1' has such large stiffness that it cannot be straightened and towed to the fish farm location like a prior art floating ring tubular, the float ring 1 according to the invention is manufactured such that a series of elements 1' , for example eight elements 1', are manufactured having the desired radius of curvature r and a length equal to 1/8 of the float ring 1 circumference, are towed to the fish farm location where they are assembled to a continuous ring by for example welding according to prior art .

The element 1' may also be formed as straight lengths and used as a floating walkway between shore and a fish farm net pen, or as a walkway between boats in a small craft harbour.

Claims

P a t e n t c l a i m s

1. A float ring (1) for a fish farm net pen arranged to be able to be arranged in a mass of water (4) , c h a r a c t e r i s e d in that - the float ring (1) is constituted by one or more elements (1') formed by extrusion of at least one material, the specific weight of the at least one material decreasing in a direction from the surface (111) of the element (1') toward the core (112) of the ele- ment , and an in the working position of the element (1') upward facing portion of the surface (111) of the element (1') forms a walkway (14) .

2. A float ring (1) according to claim 1, c h a r a c - t e r i s e d in that the cross-section of the element (1') has a mid portion (lie) which in the working position of the element (1') has an in the vertical direction smaller draught than the draught for the adjacent side portions (11a, lib) in the cross-section of the element (1') •

3. A float ring (1) according to claim 1, c h a r a c t e r i s e d in that the walkway (14) is provided with raised walkway thresholds (141) .

4. A float ring (1) according to claim 1, c h a r a c - t e r i s e d in that there in the walkway (14) are arranged a series of friction elements (142) .

5. A float ring (1) according to claim 1, c h a r a c t e r i s e d in that the friction elements (142) are formed as ridges in the walkway (14) .

6. A float ring (1) according to claim 1, c h a r a c t e r i s e d in that the friction elements (142) are constituted by mineral particles fastened in the material surface (111) .

5 7. A float ring (1) according to claim 1, c h a r a c t e r i s e d in that the float ring is provided by a series of elements (1') being rigidly interconnected.

8. A method for manufacturing a float ring (1) for a fish farm net pen, characterised in that o - at least one element (1') is formed by extrusion of at least one material the specific weight of the at least one material decreasing in a direction from the surface (111) of the element toward the core (112) of the element (1'), as there on an in the working posi-5 tion of the element (1') upward facing surface (111) of the element is formed a walkway (14) at the extrusion the float ring (1) is formed in that a first end portion (Ia) on the at least one element (1') is 0 joined with a second end portion (Ib) .

9. A method according to claim 8, c h a r a c t e r i s e d in that the element (1') is formed with a radius of curvature (r) essentially equal to the radius

(R) of the float ring (1) . 5 10. A method according to claim 8, c h a r a c t e r i s e d in that during the extrusion there is formed friction elements (142) in the surface (111) of the walkway (14) .

11. A method according to claim 8, c h a r a c t e r -o i s e d in that the walkway (14) is provided with a friction coating (142) being provided by a series of mineral particles being fastened in the surface (111) of the walkway (14) .

12. A method according to claim 11, c h a r a c t e r i s e d in that the mineral particles are fastened in the surface of the walkway (14) by the use of an adhesive or by forcing the particles into the extruded material .

13. A method according to claim 12, c h a r a c t e r i s e d in that the mineral particles are heated be- fore being forced into the surface (111) of the walkway (14) .

14. A method according to claim 10, c h a r a c t e r i s e d in that the frictional elements are machined by rolling.

15. A method according to claim 8, c h a r a c t e r i s e d in that the end portions (Ia, Ib) are joined by welding.

16. Use of an element 1' according to any claim 1-7 as a floating walkway.