MOORING SYSTEM FOR MOORING A FLOATING OBJECT

Abstract

A mooring system used for mooring a floating object, comprising a mooring line configured for extending between said object floating in water and an anchoring device, characterized by that said mooring line is made from polyoxymethylene and the ratio of static stiffness to dynamic stiffness of said mooring line is in a range of 0.8 to 1.

Claims

1. A mooring system used for mooring a floating object, comprising a mooring line configured for extending between said object floating in water and an anchoring device, wherein said mooring line is made from polyoxymethylene and the ratio of static stiffness to dynamic stiffness of said mooring line is in a range of 0.8 to 1.

2. The mooring system according to claim 1, wherein said static stiffness and dynamic stiffness are in the range of 7 to 15 GPa.

3. The mooring system according to claim 1, wherein said mooring line is a polymer rope made from a plurality of polymer monofilaments laid in a spiral shape.

4. The mooring system according to claim 3, wherein said plurality of polymer monofilaments have a diameter between 0.5 mm and 5 mm.

5. The mooring system according to claim 1, wherein said mooring line is a single braided rope consists of equal number of left and right handed strands made from multifilament fiber yarns.

6. The mooring system according to claim 1, wherein said mooring line is a laid rope comprising strands laid in a helical manner and made from multifilament fiber yarns.

7. The mooring system according to claim 1, wherein said mooring line has a tensile strength above 500 MPa.

8. The mooring system according to claim 1, wherein said mooring line is a polymer rope sheathed by a jacket.

9. The mooring system according to claim 8, wherein the polymer of said polymer jacket is selected from the group consisting of epoxy, polyamide, polyurethane, polyester (PES), polyethylene terephthalate (PET), nylon (PA), polypropylene (PP), polyethylene (PE), polypropylene-polyethylene (PP-PE) copolymer, polyethylene napthalate (PEN), high modulus polyethylene (HMPE), polyester polyacrylate (LCP), para-aramid, aramid copolymer, and any combination or blend of the above.

10. The mooring system according to claim 1, wherein said mooring line has an elastic elongation above 10%.

11. The mooring system according to claim 1, wherein said mooring line is a polymer rope having a diameter between 100 mm to 300 mm.

12. The mooring system according to claim 1, wherein the polymer of said polymer rope has at least 60% crystallinity.

13. The mooring system according to claim 12, wherein at least 50% of the crystalline polymer is orientated.

14. The mooring system according to claim 1, wherein said floating object is a floating marine energy converter platform, an offshore wind farm, a single point mooring buoy or a floating offshore oil and gas platform.

Description

BRIEF DESCRIPTION OF FIGURES IN THE DRAWINGS

[0052] The following detailed description makes reference to the accompanying drawings, in which:

[0053] FIG. 1 illustrates static-dynamic stiffness model of two different type of material.

[0054] FIG. 2 illustrates the stress strain behaviour of POM compared with nylon and PET.

[0055] FIG. 3 illustrates a cross-section of a spiral strand rope used for the mooring system according to the invention.

MODE(S) FOR CARRYING OUT THE INVENTION

[0056] A polymer rope was made according to the present invention. Wire production starts with melt extrusion of polymer pellets to product a rod, which is then drawn into a polymer wire with improved properties over the raw material. Monofilament POM wire is made by conventional wire drawing process. Similar to the work on the high tensile steel wire, the production of the polymer wires including quality of the extruded rod and process control during wire drawing is comparable to the processing of steel wire.

[0057] Larger wires may be spun layer by layer in alternate direction creating a stiffer structural type of rope, referred to as a spiral strand rope. The cross-section of such a spiral strand rope 30 is illustrated in FIG. 3. This torsional balanced construction imparts no rotational load to attached mooring components. This closed structure is inherently more resistant to water ingress and any subset corrosion. Furthermore, an extruded jacket 32 as shown in FIG. 3 can be applied to exclude water, enhancing the design life.

[0058] The polymer wires produced have been utilized to manufacture e.g., an 84 mm diameter sheathed spiral strand rope. The polymer wires take a level of plastic deformation without damage to the product; hence it is possible to impart a preformation on the wires to aid with consistent and precise rope manufacture. The level of deformation in the wires at formation point of the rope is relatively low due to the long helix geometry of the spiral strand rope constructioneach layer of the wires being added in an individual pass through the machine. However, it was noted that there were no detrimental effects on the wires, and it is anticipated that more complex constructions with a greater degree of relative deformation could be effective.

[0059] The component wires are of suitable diameter and material properties such that they are robust and inherently abrasion resistant. However, the external sheathed jacket 32 acts as an extra precautionary aid against installation damage and as its weight is not a concern, its presence is not detrimental to performance. The sheathed jacket 32 also serves to increase the stiffness of the product. Beneficial elements such as the longitudinal marker line 34 to identify any twist during deployment would remain present.

[0060] Application of the sheathed medium density polyethylene jacket is applied via tube on sheathing process. During the rope manufacture, it was also established that the processing temperature of the jacket material does not influence the properties of the wire.

[0061] The stress-strain characteristics of the invention rope (curve C) is compared with high strength fiber nylon (curve B) and high strength PE (curve A) in FIG. 2. As can be seen from FIG. 2, the breaking tenacity of the invention rope continues to increase up to 35% strain. The stress-strain characteristics of the invention rope is regressive in comparison with nylon and PE. This results in a relative increase in static stiffness and a relative decrease in dynamic stiffness values. Thus, the static and dynamic stiffness value of the invention rope are similar, and the invention rope presents a linear stiffness as shown by cure II in FIG. 1.