ANCHORING DEVICE

Abstract: Apparatus for anchoring a structure to the sea bed, comprising a crook (3) which overlaps a portion of the structure to restrict its upward movement, and a locking latch (9) which engages below a surface on the structure to restrict its downward movement, so that the crook and the latch cooperate to hold the structure in position on the sea bed.

Description: This invention relates to an anchoring device for use in anchoring structures to the seabed. Lightweight seabed structures are generally anchored in position by anchor piles which have crook devices at their upper end which hook over a spar of the structure to retain the structure in place on the seabed. A problem arises with such apparatus if the seabed should become eroded around the base of the structure. The structure may then drop slightly away from the crook device on the anchor pile so that the anchor pile no longer retains the structure in position. The structure may thus be capable of a considerable degree of movement. According to the present invention there is provided an anchoring device for a structure comprising an anchor for securing the structure to the sea bed, abutment means on the anchor in the form of a crook for engaging at least a portion of the structure to restrain the structure against upward movement in a first direction, characterised in that a latch is provided on the anchor for engaging at least a portion of the structure to restrain the structure against movement in a second direction opposite to said first direction, the latch being movable relative to the anchor to allow installation of the anchor against the structure with the latch disengaged. Further according to the invention there is provided an anchored structure on the sea bed wherein the structure is engaged by abutment means on the anchor to restrain the structure against upward movement in a first direction and by a latch on the anchor to restrain the structure against movement in an opposite direction, the latch being movable relative to the anchor to allow installation of the anchor against the structure with the latch disengaged and thereafter movement of the latch into its engaged position. Preferably the latch is in the form of a steel plate pivotally mounted on an upper section of the anchor and extending upwardly therefrom. The latch may be pivotally mounted on the anchor so as to move between a first position in which it engages the structure to prevent its movement in said opposite direction and a second position in which it allows movement of the anchoring device past the structure. Preferably the latch is arranged so that it wedges against the structure on relative movement between the anchor and structure, in a manner whereby the wedging effect causes the abutment means to be forced into closer engagement with the structure. The latch preferably acts to prevent downward movement of the structure relative to the anchor in the event of sea bed erosion, and preferably the latch engages in a socket formation on the structure at an angle of between 15 degrees and 25° to the vertical, most preferably 20°. Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a side view of an underwater structure anchored to the seabed by an anchor pile incorporating a latch device in accordance with the present invention; Fig. 2 is an enlarged side view of detail A of Fig. 1; and Fig. 3 is a plan view of the detail of Fig. 2. Referring to the drawings, one embodiment of anchor pile apparatus incorporating a latch device comprises an anchor pile 1 which extends downwardly through a thrustbox 2. The thrustbox 2 has a crook 3 extending from its upper section. A flange 4 on the upper end of the anchor pile 1 has a flange assembly 6 welded to it. The assembly 6 comprises a pair of side supports 7 which have a hinge pin 8 extending between them. A latch 9 in the form of a 100 mm wide section of steel plate is mounted on the pin 8. A structure 10 which is to be anchored has a perimeter tube 11 at its base and a series of main structural tubular members 12 extending upwardly from the base. At the lower end of each member 12 there is an abutment in the form of a horizontal welded plate projection 13 which together with a vertical plate 15 extending from it forms a socket 14. In use a structure 10 is positioned on the sea bed and a number of piles are used to retain it in position. In the example illustrated eight piles would be required though in Fig. 1 only two piles are illustrated. Each anchor pile 1 is driven into position so that the crook 3 on the thrustbox 2 engages the perimeter tube 11. At the same time the latch 9 rides over the the edge of the upper plate 13 forming the socket 14 and pivots into position in the socket 14. In that position the latch is at an angle of 20° to the vertical. The anchor pile 1 is then driven no further. The process is repeated for each anchor pile 1. The structure 10 is thus retained in position by the crook 3 and the structure 10 is supported by the latch 9 which prevents downward movement. If erosion of the seabed should subsequently take place around the base of the structure then the structure would tend to settle. Thus the vertical downward load on each latch 9 will increase. As the latch 9 is mounted on the hinge pin 8 the downward load will tend to cause the latch to pivot in a clockwise direction, as viewed in Fig. 2, to bear against an upright wall of the socket 14. The structure 10 is thus biassed to the right, again as viewed in Fig. 2. A small movement of the structure 10 is possible because of an installation tolerance of some 20mm on either side of the perimeter tube 11. This tolerance is soon taken up and the perimeter tube 11 then locks against the side of the crook 3 preventing further sideways movement of the structure 10. The structure 10 is thus retained firmly in position. Modifications and improvements may be incorporated without departing from the scope of the invention. For example, a single bracket or the like can be welded or otherwise secured to the perimeter tube or structural tubular member to provide both the socket for engagement with the latch and an abutment for engagement with the crook. This allows the shape and size of the bracket to be selected as desired, without being tied to the shape and size of the perimeter tube, as in the above embodiment. The bracket can then be rectangular in cross-section instead of circular, which provides a greater area of contact with the crook and reduces the possibility of rotation of the structure in the event of failure of the remote anchor piles; a rectangular-section bracket will mate with the faces of the crook more closely than the circular-section perimeter tube.

Claims: An anchoring device for a structure (10) comprising an anchor (1) for securing the structure (10) to the sea bed, abutment means on the anchor (1) in the form of a crook (3) for engaging at least a portion (11) of the structure (10) to restrain the structure (10) against upward movement in a first direction, characterised in that a latch (9) is provided on the anchor (1) for engaging at least a portion (14) of the structure (10) to restrain the structure against movement in a second direction opposite to said first direction, the latch (9) being movable relative to the anchor (1) to allow installation of the anchor (1) against the structure (10) with the latch (9) disengaged. An anchoring device as claimed in Claim 1, wherein the latch (9) is pivotally mounted on the anchor (1). An anchored structure (10) on the sea bed wherein the structure (10) is engaged by abutment means on the anchor in the form of a crook (3) to restrain the structure against upward movement in a first direction and by a latch (9) on the anchor to restrain the structure (10) against movement in an opposite direction, the latch (9) being movable relative to the anchor (1) to allow installation of the anchor (1) against the structure (10) with the latch (9) disengaged and thereafter movement of the latch (9) into its engaged position. An anchored structure (10) as claimed in Claim 3, wherein the structure has a formation (14) thereon which engages with the latch (9) in a manner whereby movement of the structure (10) in said opposite direction causes the latch (9) to engage more securely against the formation (14). An anchored structure as claimed in Claim 4, wherein the formation is a socket within which the latch engages. An anchored structure as claimed in Claim 3, 4 or 5 wherein the latch (9) is pivotally mounted on the anchor (1). An anchored structure as claimed in Claim 6, wherein the latch (9) engages with the structure (10) at an angle of between 15 degrees and 25 degrees to said opposite direction. An anchored structure as claimed in any one of Claims 3 to 7, wherein the latch (9) is arranged so that on relative movement of the structure (10) and the anchor (1) in said opposite direction the latch (9) wedges against the structure (10) in a manner whereby the structure (10) is biassed into engagement with the abutment means (3).

Inventors: MARTIN, ROBERT GEORGE
Applicants: ANCHORTECH LIMITED
Application year: 1987
Main classification: E02D27
IPC codes: E02D27