WO2022112421A1

WO2022112421A1 - Spherical mooring thimble

Info

Publication number: WO2022112421A1
Application number: PCT/EP2021/083011
Authority: WO
Inventors: Torkjell Lisland
Original assignee: Seasystems As
Priority date: 2020-11-26
Filing date: 2021-11-25
Publication date: 2022-06-02
Also published as: NO346535B1; NO20201305A1

Abstract

A device for connecting a mooring line (21, 22, 23) to a bracket (35, 36) that is directly or indirectly coupled to a floating structure, said device being capable of rotation about at least two axes. The device comprises a thimble (25, 26, 27) attached to said mooring line (21, 22, 23), said thimble (25, 26, 27) carrying a first bearing part (33) of a spherical bearing, and said bracket carrying a second part (34) of a spherical bearing.

Description

SPHERICAL MOORING THIMBLE

Technical Field

[0001] The present invention relates to mooring devices, in particular single point moorings where a multiple of mooring lines extends from different fixed points, such as a seabed anchors to a single point on a floating vessel or a buoy.

[0002] The invention pertains to a connection device for connecting mooring lines to a floating structure, such as a vessel or a buoy. It is in particular suitable for connecting mooring lines to a turret that is coupled to a vessel or a buoy. However, the connecting device may also be used to connect mooring lines to a floating wind turbine foundation, a floating wave power or solar power facility, floating fish farming cages, floating docks or quays, etc.

Background Art

[0003] The prevailing method of fixating mooring lines to a vessel or a buoy is through a universal joint. The universal joint consists in general of two bolts that form an axis of rotation and are arranged at right angles to one another with a link between the bolts. Examples of such joints are shown in figures 1 and 2.

[0004] Figure 1 shows a termination of mooring lines comprising a sturdy first bolt 1 arranged generally horizontal and supported by a pair of ears 2, 3 on a structure attached to a vessel. A link 4, having a sleeve 5 and an ear 6 formed integral with the sleeve 5 is journaled around the first bolt 1. A forked end termination 7 is coupled to the ear 6 by a second bolt 8, which is set at right angle to the first bolt 1. The end termination is crimped or otherwise firmly attached to the end of a mooring line 9.

[0005] Figure 2 shows another type of joint where the structure attached to the vessel har one ear 10. A link 11 is attached to the ear 10 via a generally horizontal bolt 12. The link 11 is forked at both ends, but the slits defining the forked ends are set at right angles to one another. At its outer end, the link 11 is attached to a round thimble 13 that is spliced to a mooring line 14.

[0006] Although, the above explained devices for fixating mooring lines, as well as similar devices based on a universal joint, have proven to be relatively reliable, there are some inherent drawbacks. These devices require at least two separate bearings, one at each bolt. The bearings need to take a substantial degree of movement in both the horizonal and vertical plane.

[0007] Until recently it has been the prevailing choice to use either steel wire or wrought iron chain, at least close to the termination to the vessel or buoy. Especially wrought iron chain is subjected to corrosion. This means that the chain has to be made thicker to allow for the material reduction that inevitably will happen over time. A thicker, and hence heavier, chain means that the couplings to the vessel or buoy has to me made stronger, such as the one shown in figure 1 . The strength of the fixation to the vessel has to be at least equal to the chain itself.

[0008] Fibre ropes, especially High Modulus Synthetic Fibre (HMSF), such as Aramid, Liquid Polymer and Polyethylene, have gained increasing popularity in the recent years. Such ropes are light, strong and flexible. The connection shown in figure 2 is adapted for coupling to a rope. It is lighter than the one shown in figure 2, but as can be clearly seen, it has a long moment arm, especially for forces with a component in the horizontal plane. The arm is from the thimble to the centre of the turret.

[0009] It is therefore a need for a new type of connection between a mooring line and a vessel or a buoy that is both lighter and have a shorter moment arm.

Summary of invention

[0010] The above problems of the prior art solutions are solved by the present invention by a device for connecting a mooring line to a bracket that is directly or indirectly coupled to a floating structure, said device being capable of rotation about at least two axes, characterised in that it comprises a thimble attached to said mooring line, said thimble carrying a first bearing part of a spherical bearing, and said bracket carrying a second part of a spherical bearing.

[0011] In a preferred embodiment, said second bearing part encircles a circumference of a bolt that is suspended in said bracket.

[0012] In a further preferred embodiment, said bolt is arranged in said bracket with its axis transversely to a prevailing direction of said mooring line.

[0013] In an alternative embodiment, said bolt is arranged with its axis in a vertical plane. [0014] In a further alternative embodiment, said bolt is arranged with its axis in a horizontal direction.

[0015] Preferably, said thimble comprises a circular curved first part and a wedge shaped second part adjoining said first part, and that a groove to receive an eye of said mooring line is formed along the circumference of said thimble.

[0016] Further preferably, said thimble has an opening into which said first bearing part is mounted, said first bearing part being concave.

[0017] Even further preferably, said second bearing part is convex.

[0018] Also further preferably, said second bearing is sandwiched between a pair of sleeves attached to a respective ear of said bracket, said sleeves supporting said bolt.

[0019] Further preferably, the device comprises at least one end stop, against which said thimble abuts before the bearing reaches its outer limit.

[0020] The invention also relates to a turret comprising a plurality of connecting devices according to the invention, wherein said plurality of connecting devices are mounted to said turret at equiangular distances.

[0021] The turret may have a ring-shaped end stop is mounted below, above or on both sides of said plurality of connecting devices, said thimbles of said connecting devices abutting said ring-shaped end stop before the bearings of said connecting devices reach their outer limit.

Brief description of drawings

[0022] The invention will now be explained in further detail, referring to the enclosed drawings, in which:

Figure 1 shows a first prior art solution, as explained above,

Figure 2 shows a second prior art solution, as explained above,

Figure 3 shows an embodiment of a connecting device according to the invention in isometric view,

Figure 4 shows the device of figure 3 in a different view,

Figure 5 shows a longitudinal section through the connecting device of figures 3 and Figure 6 shows the same longitudinal section as in figure 5, but with the thimble turned downwards to its maximum deflection.

Detailed description of the invention

[0023] Referring first to figure 3, the connecting device of the invention is shown to connect three mooring lines 21 , 22, 23 coupled to a turret 24. At the opposite end, the mooring lines may be coupled to an anchor on the seabed, or they may be fixed at shore or to another vessel or buoy. The turret 24 may be received in a floating vessel, a buoy or any other piece of equipment that is movable relative to a fixed location but is attached to said location by mooring lines, such as, but not limited to, wind turbine foundations, wave power or solar power facility, fish farming cages, floating docks or quays, etc.

[0024] The turret may be permanently fixed to the vessel or buoy but may also be removable relative to said vessel or buoy.

[0025] The connecting device may also be coupled directly to the vessel or buoy without a turret.

[0026] Even though three mooring lines and three connecting devices are shown here, the number of mooring lines and connecting devices may vary between a single and a substantial number.

[0027] The mooring lines shown, extend in a star-like formation from the seabed in the shown embodiment. However, they may be arranged in other configurations, such as extending substantially parallel to a respective connecting device, said connecting devices being arranged side by side.

[0028] The mooring lines may be ropes, such as synthetic ropes, but may also be steel wire.

[0029] Each mooring line 21 , 22, 23 are spliced with a thimble 25, 26, 27 arranged in the eye of the splice. The thimble 25, 26, 27 is generally drop shaped with a circularly curved part 28 and a wedge-shaped part 29 adjoining the curved shaped part 28. The circular shaped part 28 has an opening 30 adapted to receive a bearing (see figure 5). An additional aperture 32 is made in the wedge-shaped part, but this is purely for weight and material reduction. [0030] The thimble 25, 26, 27 receives a bolt 33, which carries a bearing 34 (see figure 5). This will be explained in further detail below.

[0031] The bolt 33 is supported at each end by bracket comprising a pair of ears 35, 36. The ears 35, 36 are fixedly attached to a support structure 37, which in turn is attached to the turret 24.

[0032] The support structure 37 is equipped with a movement delimiter 38 in the form of a ring.

[0033] Figure 4 illustrates a normal angular range of movement of the mooring line about the connecting device. This is the movement in the plane that is transverse to the axis of the bolt 33. In normal operation the angular range may for instance be +/- 20°, but the mooring lines have to be able to move substantially beyond this range. If one of the three mooring lines should break, the remaining two lines will travel over an angular distance that may be +/-90° or more.

[0034] Figure 5 shows the connecting device in a longitudinal view. In this view the turret 24 has been received in the hull 39 of a vessel. The turret 24 is supported by bearings, of which a lower bearing 40 is shown. The turret may therefore rotate relative to the vessel.

[0035] As can be seen in this view the bolt 33 is fixedly retained between the ears 35, 36 and received in a pair of sleeves 41 , 42 that are welded or otherwise fixedly attached to the ears. The sleeves 41 , 42 and the bolt 33 together supports an inner bearing part 34. The inner bearing part 33 has an outer convex spherical bearing surface 33a. Inside the opening 30 in the thimble 26 is arranged an outer bearing part 33 that is complementary to the inner bearing part 34, so that the outer bearing part 34 has an inner concave spherical bearing surface 34a of the same curvature as the bearing surface 33a of the inner bearing part.

[0036] The ears 35, 36 are set at a downward angle relative to the horizontal plane. The bottom of the hull 39 is also generally horizontal. Figure 5 shows the mooring line 22 extending at the same downward angle as the ears 35, 36. This is the neutral position of the vessel relative to the mooring. The mooring lines will from this orientation be allowed to move a certain angle upwards and downwards in the vertical plane. As the mooring line moves over this range, the bearing parts 33, 34 moves relative to one another by sliding across the bearing surfaces. [0037] Figure 6 shows the mooring line at its furthest downward angular position. In this position the thimble is prevented from moving further down by the ring 26. A similar ring above the thimble 26 may also be present to stop an angular deflection of the thimble 26 before it reaches the limits of the spherical bearing 30, 34.

Claims

1. A device for connecting a mooring line to a bracket that is directly or indirectly coupled to a floating structure, said device being capable of rotation about at least two axes, characterised in that it comprises a thimble attached to said mooring line, said thimble carrying a first bearing part of a spherical bearing, and said bracket carrying a second part of a spherical bearing.

2. The device of claim 1 , characterised in that said second bearing part encircles a circumference of a bolt that is suspended in said bracket.

3. The device of claim 2, characterised in that said bolt is arranged in said bracket with its axis transversely to a prevailing direction of said mooring line.

4. The device of claim 2 or 3, characterised in that said bolt is arranged with its axis in a vertical plane.

5. The device of claim 2 or 3, characterised in that said bolt is arranged with its axis in a horizontal direction.

6. The device of any of the preceding claims, characterised in that said thimble comprises a circular curved first part and a wedge shaped second part adjoining said first part, and that a groove to receive an eye of said mooring line is formed along the circumference of said thimble.

7. The device of any of the preceding claims, characterised in that said thimble has an opening into which said first bearing part is mounted, said first bearing part being concave.

8. The device of any of the preceding claims, characterised in that said second bearing part is convex.

9. The device of any of the preceding claims 2-8, characterised in that said second bearing is sandwiched between a pair of sleeves attached to a respective ear of said bracket, said sleeves supporting said bolt.

10. The device of any of the preceding claims, characterised in that it comprises at least one end stop, against which said thimble abuts before the bearing reaches its outer limit.

11. A turret comprising a plurality of connecting devices according to any of the claims 1-10, characterised in that said plurality of connecting devices are mounted to said turret at equiangular distances.

12. The turret of claim 11 , characterised in that a ring-shaped end stop is mounted below, above or on both sides of said plurality of connecting devices, said thimbles of said connecting devices abutting said ring-shaped end stop before the bearings of said connecting devices reach their outer limit.