CHAIN TABLE FOR A TURRET OF A VESSEL

Description

Field of the invention

[0001] The present invention relates to a chain table for a turret of a vessel floating in the sea, in particular a vessel for storing hydrocarbons such as a Floating Production Storage and Offloading (FPSO) vessel, Floating Storage and Offloading (FSO) vessel or Floating Liquefied Natural Gas (FLNG) vessel, wherein the chain table comprises a main body with a top end and a bottom end and an outer surface extending therebetween around a longitudinal axis of the main body, and wherein the main body is provided with a plurality of connector points on its outer surface for connecting to the end of an anchor line. The invention further relates to an anchoring system and vessel comprising such a chain table, and to a method of attaching a chain table to a turret.

Background art

[0002] Traditionally, installation of an anchoring system and riser system for connection to a turret of a vessel is performed in two distinct stages. During a first stage, the anchoring system and riser system are pre-laid, i.e. are attached to the sea bed in an area where hydrocarbons are to be extracted from the sea bed, before the vessel arrives in the area. The anchoring system generally comprises anchor lines and anchors connecting these to the sea bed, and the riser system generally comprises risers or hoses for transporting hydrocarbons from the sea bed to the turret. Each of these risers or hoses is connected at one end to a well head in the sea bed and is to be connected at the other end to the turret. During a subsequent second stage the vessel on which the turret is mounted, sails to the area. Once it has arrived the other ends of the anchor lines are retrieved one by one by an installation vessel. After retrieval, each anchor line end is transported to turret where it is pulled in and connected to the turret. Next, the installation vessel retrieves the risers and transfers these to the vessel for connection to the turret.

[0003] A drawback of this traditional manner of installation is that individually connecting and pulling in a sufficient number of anchor lines in order to connect the turret in a stable manner to the sea bed takes a significant amount of time. The required time may be greater than a time window during which weather conditions are favourable for connecting anchor lines to the turret. This is particularly relevant in areas where the weather is often stormy.

[0004] To at least partially overcome this drawback, European patent EP 2 303 680 B1 in the name of applicant proposes a disconnectable turret mooring system for a vessel, said system comprising a mooring buoy member and a turret structure mounted in a moonpool of the vessel, the mooring buoy member being anchored to the sea bed with mooring lines and having a plurality of passages each adapted for receiving a riser, the turret structure having a receptacle for receiving the buoy member and one or more locking devices for locking the buoy member in the receptacle, the turret structure accommodating a plurality of conduits to be connected to risers installed in passages of the buoy member, and wherein the turret structure is rotatably supported in the moonpool of the vessel by means of at least one bearing assembly mounted above sea level. The known mooring system is able to support a large number of risers, for example at least 20 risers and incorporates a disconnection / reconnection capability to allow an FPU (floating production unit) vessel to disconnect from its anchoring system when for instance iceberg warnings are issued. Though the known system significantly reduces the time required for connecting anchor lines to a turret, it is relatively complex.

[0005] In is an object of the present invention to provide a chain table of a simple construction which allows fast coupling of anchor lines to a turret of a vessel.

[0006] The invention further provides an assembly comprising such a chain table, as well as a method for installing such a chain table

Summary of the invention

[0007] To this end, according to a first aspect the present invention provides a chain table for a turret of a vessel floating in the sea, wherein said turret is adapted to rotate in a moonpool of the vessel, said chain table comprising a main body with a circumferential top edge, a bottom surface and an outer surface extending therebetween around a longitudinal axis of the body, wherein said body is provided with a plurality of connectors arranged along said outer surface and adapted for connecting to an end of an anchor line, wherein the connectors are partitioned into different sets of connectors, wherein each set is arranged at a height along said longitudinal axis that differs from the height of the other sets and is spaced apart from said bottom surface, and wherein said chain table is adapted for sinking to the sea bed and is further adapted for attachment to the turret with said longitudinal axis extending substantially vertically. As the chain table can simply sink to the sea bed it is suitable for use at any sea depth and in particular does not require any air-filled floatation chambers, pumps, valves and/or moving parts for keeping the chain table suspended in the water at a predetermined height. This allows the chain table according to the invention to be of a particularly simple construction. The chain table can be sunk to the sea bed with the ends of the anchor lines already attached to the connectors, or the anchor lines may be attached to connectors after the chain table has completely sunk and is supported on its bottom surface by the sea bed. In either case, the chain table may be positioned at an intended position relative to the sea bed independent of the position of the vessel and/or turret, e.g. when the vessel and/or turret are not yet in a position close to the intended position or even when construction of the vessel and/or turret has not yet been completed. As the chain table, when sunk to the sea bed, is completely supported by the sea bed and the anchor lines may lie on the sea bed as well, the total suspended weight of the anchoring system while the chain table is located on the sea bed is minimized.

[0008] Once the vessel and turret have reached the intended position, the chain table and the anchor lines connected thereto can jointly be pulled up in a single haul-in action and subsequently the chain table is fixed to turret to achieve very fast coupling of the anchor lines to the turret. The chain table is preferably provided with a cable attachment element, e.g. comprising one or more cable pulling eyes at or near its longitudinal axis, for connection with a cable for pulling the chain table up from the sea bed and towards the turret such that when the chain table is pulled against the turret its longitudinal axis is substantially vertical. Pulling up of the chain table by the cable causes the chain table to be substantially aligned with a vertical axis which preferably coincides with a substantially vertical axis of rotation around which the vessel can weathervane around the turret. During pulling up of the chain table the total weight of the chain table and anchor lines connected thereto that have to be supported by the vessel can remain relatively low as the chain table is not connected to any risers or the like. Once the chain table has been attached to the turret and securely fixed the turret to the sea bed, the risers can be retrieved and attached to the turret without passing through the chain table.

[0009] In an embodiment the chain table has an elongated shape extending along the longitudinal axis of the body, and the chain table is adapted, when supported by the sea bed, to be supported substantially completely on its bottom surface in such a manner that said longitudinal axis is substantially vertical, with the connectors spaced apart from said bottom surface. When the chain table is supported on its bottom surface, the weight of the chain table is substantially supported by the bottom surface and the connectors are not loaded with the weight of the chain table. Importantly, when the chain table is of the type that is sunk to the sea bed before the ends of the anchor lines are attached to the connectors, the present embodiment allows these ends to be inserted in the connectors even when the chain table is supported on its bottom surface. Generally, the weight of the chain table, e.g. one hundred thousand kg or more, will allow it to be supported with its bottom surface on the sea bed in a stable manner.

[0010] In an embodiment the chain table has a density of more than 1.03 grams per cubic centimeter, preferably more than 7 grams per cubic centimeter .The density of the chain table ensures that it will sink to the sea bed, even in deep water. The density as a ratio of weight vs. volume of the chain table can be determined by measuring, preferably at 20 °C and an absolute air pressure of 1 atmosphere, the weight and volume of the chain table. The volume can conveniently be measured by filling a basin with water of a known density and measuring the mass of water that is displaced when the chain table is completely submerged in the water.

[0011] In an embodiment, the chain table comprises one or more buoyancy elements made from a syntactic foam, preferably a metal syntactic foam. Syntactic foams are able to withstand large pressures without collapsing, and the buoyancy elements help to reduce the downward force exerted by the chain table on the turret both when it is suspended from the turret, e.g. by a cable, and when the chain table is fixedly attached to the turret.

[0012] In an embodiment, the body is provided with an air chamber which is open ended at the bottom surface of the body and adapted to be filled with air. When the chain table is supported by its bottom surface on the sea bed additional buoyancy for the chain table may be provided by injecting air into the air chamber at a pressure corresponding to the depth at which it is supported on the sea bed. During hauling in of the chain table the air can escape through the open end at the bottom surface.

[0013] In an embodiment each of said connectors is arranged on the body in a row, each row comprising one or more connectors from each set, wherein, when viewed in projection on a plane perpendicular to the longitudinal axis, the connectors in each row are spaced at an angular distance of at least 90 degrees from connectors in adjacent rows, preferably at least 110 degrees. This arrangement provides space for risers and/or hoses to pass between the rows of connectors and anchor lines connected thereto towards the turret. Connectors in a same set which are spaced at an angular distance less than 90 degrees from each belong to a same row. The angular distance between two connectors is here defined as an angle between a first line between a point of attachment of one of said connectors to the circumferential outer surface and the longitudinal axis, and a second line between a point of attachment of the other of said connectors to the circumferential outer surface, when viewed in said projection onto said plane normal to the longitudinal axis.

[0014] In an embodiment the rows are spaced equidistantly along the circumference of the outer surface. For example, if all connectors of each row belong to different sets, then the chain table may comprise three such rows, each consisting of three connectors arranged at three different heights along the body.

[0015] In an embodiment one or more of said rows comprise multiple connectors of a same set, preferably wherein the angular distance between connectors of each set within a row decreases with the distance of said connectors to the bottom surface. For example, if the body has connectors arranged in three sets along a top, middle and lowest height, each row may have two connectors at the top height at a first angular distance from each other, two connectors at the middle height at a second angular distance from each other which is smaller than the first angular distance, and at the lowest height, which is closest to the bottom surface, a single connector arranged within plane parallel to and through the longitudinal axis of the body.

[0016] In an embodiment each of the connectors comprises a substantially rigid arm having a proximate end pivotably connected to said body via one or more pivots and having a distal end adapted for connection to the end of an anchor line. Each rigid arm ensures that each the anchor line connected thereto remains spaced apart from the body of the chain table, while the pivotable connection allows some movement between the end of the anchor line and the body. The one or more pivots preferably comprise a first hinge allowing the arm to pivot around a first pivot axis, and a second hinge allowing the arm to pivot around a second pivot axis which is perpendicular to the first pivot axis. For facilitating attachment of the distal end of the arm to the end of the anchor line, the distal end may be provided with an anchor swivel or the like. Preferably, the extent to which each arm can pivot in a plane parallel to the longitudinal axis is restricted to predetermined range such that each arm is prevented from contacting another arm of the chain table as well as the outer surface of the chain table. This may be achieved for instance by attaching limiter plates to the chain table above and below the proximate end of each arm, which plates limit pivoting of said arm, e.g. to within an angle from +20 to -20 degrees relative to the longitudinal axis when seen in a plane parallel to said axis.

[0017] In an embodiment said arms are arranged to allow one or of said risers to pass between neighboring arms in each set on an outer side of said outer surface. The risers may thus pass partially between the arms on toward the bottom surface of the turret, particularly when the connectors are arranged in rows as described herein.

[0018] In an embodiment said body comprises a hollow interior defined by said bottom surface and outer surface, wherein the chain table is provided with a number of through openings for allowing substantially free passage of water into and out of said interior from an outer surface of said chain table when the body is submerged in the water. The chain table can thus be constructed without large hollow compartments with interiors that cannot be reached by the water and which may deform due to pressure differences, and the same chain table may be used in very deep water (e.g. having a depth greater than 1000 m) or shallow water (e.g. having a depth of 200 m or less), without having to adapt the chain table. The hollow interior preferably extends along said longitudinal axis at least over the height between the set of connectors closest to the top surface and the set connectors closest to the bottom surface. More preferably, at or near each of the connectors a through opening is arranged which extends from the outer surface to the hollow interior.

[0019] In an embodiment the outer surface of said body is a cylindrical surface, said body comprising a number of annular elements on the inside of said cylindrical surface and attached thereto spaced apart from each other along the longitudinal axis. A chain table with a structurally strong body is thus provided, in particular if on an inner side of the outer surface a further cylindrical surface is provided which connects to openings of the annular elements. Moreover, when the chain table is supported on the sea bed, the cylindrical shape of the body makes it less susceptible to be rotated around its longitudinal axis by water currents which are substantially directed in a plane parallel to the sea bed.

[0020] In an embodiment the chain table is substantially made from one or more metals, metal alloys and/or a syntactic foam. The chain table may for instance substantially or completely be made from steel, or may comprise a combination of a metal and a syntactic foam. Metals, metal alloys and syntactic foams all are relatively insensitive to changes in pressure, allowing the chain table to be used at any depth.

[0021] In an embodiment the said chain table is free from riser conduits, i.e. the chain table is provided without any opening or conduit that is adapted for passage of a riser. Risers and riser conduits are relatively easily damaged, so that having these attached to the chain table would result in damage to the riser or riser conduits, in particular if these were to extend through the bottom surface of the chain table.

[0022] According to a second aspect, the present invention provides an anchoring system comprising a chain table as described herein, said system further comprising: a pedestal having lower end which extends partially into the sea bed and support surface adapted for supporting the bottom surface of said chain table thereon. By arranging the bottom surface of the chain table on a pedestal, the risk of the chain table becoming lodged in shifting soil is substantially reduced. Moreover, the pedestal provides a fixed location on the sea bed, allowing more accurate positioning of the chain table when it is supported on the sea bed, as well as more accurate positioning of the turret of a vessel when the chain table is fixedly connected to the turret to be stationary relative to the turret.

[0023] The pedestal is preferably provided with upright supports which extend to a level above the support surface and are adapted for holding the outer surface of the body of the chain table therebetween in an upright position while the chain table rests with its bottom surface on said support surface. The upright supports guide movement of the chain table along its longitudinal axis when it is pulled up, while substantially blocking rotation and translation of said chain table in a plane normal to the longitudinal axis when the bottom surface of the chain table is supported on the pedestal. Movement of the chain table in a direction other than the upward direction is thus substantially prevented.

[0024] According to a third aspect, the present invention provides a vessel which floats in the sea and comprises a moonpool in which a turret is rotatably supported, wherein said turret, at its bottom side, is provided with an opening which debouches into an accommodation space for at least partially accommodating a chain table as described herein, wherein the vessel is provided with a cable haul in mechanism adapted for hauling in a cable attached to the chain table in order to lift said chain table from the sea bed and into the accommodation space of said turret. The part of the chain table to be accommodated in the accommodation space will generally be an insertion end of the chain table. The haul-in mechanism may be arranged either on the turret, or on a vessel deck which is arranged to weathervane around the turret. In the latter case, when the chain table is being pulled up from the sea bed, rotation of the vessel around the turret is temporarily locked. Preferably, the same haul-in mechanism is used for pulling up the ends of the risers towards the bottom side of the turret.

[0025] In an embodiment the turret is provided with a plurality of riser connectors which are arranged around the opening at its bottom side. Thus, no riser connectors or conduits extend from the turret into and/or through said chain table. Instead, the riser connectors and/or any risers connected thereto may extend from a bottom side of the turret, partially between the connectors and anchor lines connected thereto, towards the sea bed.

[0026] In an embodiment the circumferential outer surface has a maximum outer diameter which is less than an inner diameter of the moonpool at the bottom surface of the turret, preferably wherein the maximum outer diameter is less than half said inner diameter of the moonpool. This allows the risers to be connected to the bottom side of the turret without passing through the chain table. The maximum outer diameter preferably is less than, or less than half, an outer diameter of the bottom side of the turret.

[0027] In an embodiment, the chain table has a maximum outer diameter greater than 5 m, preferably between 6 and 12 m, and/or the chain table has a height greater than 8 m, the entire height of the chain table preferably being between 9 and 16 m.

[0028] In an embodiment, the chain table, including the connectors but excluding any anchor lines connected thereto, weighs at least a few hundred tonnes, e.g. 200.000 kg or more.

[0029] In an embodiment the chain table comprises an insertion end extending from said main body on a side of said body away from its bottom surface, said insertion end having a maximum outer diameter which is less than the inner diameter of the moonpool at the bottom side of the turret, preferably wherein said insertion end has a maximum outer diameter which is half or less than an outer diameter of the bottom side of the turret. The insertion end can thus be moved into an accommodation section of the turret that is arranged in the moonpool. When the entire said chain table has a maximum outer diameter which is smaller - preferably less than half - than the outer diameter said of the bottom side, one or more risers or riser conduits can be connected to the bottom side without contacting and/or passing through the chain table.

[0030] Preferably the insertion end is provided with a conical section to facilitate insertion thereof through an opening in the bottom side of the turret.

[0031] In an embodiment the turret is provided with an orientation mechanism for aligning the orientation of the chain table relative to said riser connectors. Such a mechanism may for instance comprise example grooves and cooperating cams within the accommodation space and on the outer surface of the insertion end of the chain table. Alternatively, just prior to the chain table being fixed to the turret, the turret may be maneuvered to rotate relative to the chain table until the riser connectors are arranged at a position where they can pass between the connectors of the chain table and or the anchor lines connected thereto.

[0032] In an embodiment the chain table further comprises one or more engagement members and said turret comprises locking members for locking engagement, preferably permanent locking engagement, with said one or more engagement members to lock the chain table to be stationary with respect to said turret. Examples of such engagement members are protrusions and recesses in the chain table, e.g. a groove, a widened portion or flange, preferably at the insertion end of the chain table. The locking members are adapted for locking the chain table to be stationary with respect to the turret, e.g. by placing a portion of the locking member around the protrusion or into the recess of the chain table. As the chain table is not expected to be detached from the vessel, the engagement members and longing members can be kept simple. Once the one or more engagement members have been engaged by the locking members, further fixing means can be provided between the chain table and turret. Such fixing means for keeping the chain table stationary with respect to the turret may comprise welds, bolts or pins and wedges and the like, and may be attached to the chain table along different heights.

[0033] According to a fourth aspect, the present invention provides a method of attaching a chain table to a turret that is rotatably supported in a moonpool of a vessel in an area where one or more risers are provided for transporting hydrocarbons from the sea bed to the turret, said method comprising the steps of:

• during an first stage during which said vessel is not in the neighbourhood of said area:
  • attaching a plurality of anchor lines with their first ends to the sea bed in said area;
  • letting a chain table sink to the sea bed in said area, wherein said chain table has a longitudinal axis and a bottom surface and is provided with a plurality of connectors which are partitioned into different sets of connectors, wherein each set is arranged at a height along said longitudinal axis that differs from the height of the other sets and is spaced apart from said bottom surface;
• during a second stage during which said vessel is in the neighbourhood of said area:
  • positioning said vessel with its moonpool substantially above the chain table;
  • pulling said chain table and the plurality of anchor lines connected thereto up towards the turret until the chain table is partially accommodated in the accommodation space of said turret;
  • fixing said chain table to the turret and subsequently connecting the risers to the turret at a position of the turret spaced apart from the chain table. The method provides a quick way of attaching a turret to anchor lines, using a chain table which can be used in water of any depth without adjusting the chain table. For the purposes of this method, a vessel may be said to be in the neighbourhood of an area if the vessel is located within 1 mile from the area. Pulling up of the chain table may be achieved using a winch or the like that may be located either on the turret or on a deck of the vessel which deck weathervanes around the turret. Once the chain table has been pulled up and is fixed to the turret, the risers are preferably connected to riser conduits which extend from a bottom side of the turret, though alternatively the risers may be guided through the bottom side towards a deck of the turret.

[0034] In an embodiment the method further comprises, during the first stage and prior to letting the chain table sink to the sea bed, installing a pedestal on the sea bed, wherein said pedestal is adapted for supporting the bottom surface of the chain table thereon, and wherein letting the chain table sink to the sea bed comprises letting the chain table sink until its bottom surface is supported by the sea bed via the pedestal. The pedestal provides a fixed point on the sea bed, facilitating accurate positioning of the chain table with respect to the sea bed which is particularly desirable if the chain table is sunk to the sea bed while the anchor lines are not yet attached to the connectors.

[0035] In an embodiment the method further comprises, when said chain table has sunk to the sea bed and is supported on its bottom surface, attaching a second end of each anchor line to the chain table by pulling said second end into a connector of said plurality of connectors using a haul- in line connected to said second end, wherein the pulling in is achieved by hauling in the haul-in line using a haul-in mechanism that is arranged on the vessel. The anchor lines can thus be connected to the chain table after the chain table has sunk and is supported on the sea bed without employing divers or submerged vessels.

Short description of drawings

[0036] The present invention will be discussed in more detail below, with reference to the attached drawings, in which:

Fig. 1A shows a vessel with a chain table according to a first embodiment of the invention,

Fig. 1B shows a detail of section I-B of Fig. 1A,

Fig. 1C shows the chain table of Fig 1A supported on a pedestal on the sea bed,

Fig. 2A shows a vessel with a chain table according to a second embodiment of the invention,

Fig. 2B shows the chain table of Fig 2A supported on a pedestal on the sea bed,

Fig. 3A shows a main body as may be part of a chain table of the present invention,

Figs. 3B-3D schematically show cross-sectional view through the main body of Fig. 3A at three different heights,

Fig. 4 shows a vessel with a chain table according to a third embodiment of the invention.

Description of embodiments

[0037] Figs. 1A and 1B respectively show schematically a vessel 1 according to the present invention and a detail of section I-B of Fig. 1A. The vessel 1 is adapted for storage of hydrocarbons and comprises a moonpool 2 in which a turret 50 is rotatably supported in such a manner that the vessel can weathervane around vertical axis of rotation V. The turret 50 is supported in the moonpool by radial wheels 12 and on axial bogies 13. Above the level of the water surface W a seal 11 is provided between the moonpool 2 and the outer surface of turret 50, to prevent water from reaching the radial wheels 12 and axial bogies 13.

[0038] A plurality of anchor lines 80 are connected on one end to the turret via a chain table 100 according to the invention, and on another end to the sea bed (not shown), and extend downward to the sea bed at an angle β of about 50 degrees to the vertical axis V. The chain table 100 extends through a through-opening 51 in a bottom side 52 of the turret 50 and is partially accommodated in an accommodation section 53 within the turret 50. This is possible as the maximum outer diameter of the portion of the chain table 100 in the accommodation section 53 is less than half the outer diameter of the bottom side 51 of the turret. In the present example the maximum outer diameter of the chain table is about 6 m, and the total height of the chain table is about 14 meters. Riser conduits 70 extend through the bottom side 52 for connecting to risers or hoses or the like which in turn are connected to the sea bed. The conduits are arranged for the transfer of hydrocarbons that have been extracted from the sea bed and transported to the conduits via risers or the like, through the bottom side 52 of the turret and on to a swivel stack 5. For reasons of clarity, only three anchor lines 81,82,83 of the plurality of anchor lines 80 are shown in Fig. 1A, and only two conduits 71,72 of the conduits 70 are shown, though it will be clear that in practice further anchor lines are connected to the turret around the vertical axis V, and further conduits extend through the bottom side 52 at positions surrounding opening for the chain table.

[0039] The hull 3 of the vessel 1 has bottom 4 which extends substantially in a plane at a vertical distance d1 from the water surface W. The bottom surface 111 of the chain table 100 in turn is arranged at a vertical distance d2 from the bottom 4 of the hull 3, and the bottom side 52 of the turret 50 is arranged at a vertical distance d3 from the bottom 4 of the hull. As the bottom side 52 is arranged above the bottom 4 of the hull, the point of attachment of the top anchor line 81 to the chain table 100 can be at a level above the bottom of the hull and close to the center of gravity of the vessel 1.

[0040] The chain table 100 is connected to a cable 9 which extends from an eye 17 at the top of the chain table, in line with the vertical axis V, via guide wheels 6,7 to a haul-in mechanism 8 in the form of a winch that is arranged on the turret 50. Guide wheel 6 is arranged such that the portion of the cable 9 which runs from the wheel 6 down to the chain table substantially coincides with the vertical axis V. Together the guide wheels 6,7, haul-in mechanism 8 and cable 9 are adapted for pulling the chain table 50 up from a position in which the chain table 100 is arranged below and spaced apart from the turret 50 on the sea bed to the position shown in Figs. 1A and 1B. During movement of the chain table 50 from the sea bed towards the turret the longitudinal axis L of the chain table is substantially aligned with the vertical axis of rotation V which passes through the moonpool 2.

[0041] The chain table 100 comprises a main body 110 to which the plurality of anchor lines 81, 82, 83 is connected and which substantially projects out of said accommodation section 53 below the bottom side 52 of the turret. The chain table further comprises an insertion end 160 which is connected to the main body 160 and substantially projects into the accommodation section 53 above the bottom side 52. At its insertion end the chain table is fixed to the turret 50 using one or more stop blocks 54 which are rotatable around a horizontal axis 55 relative to a support platform 56 of the turret. When the annular support ring 164 of the insertion end 160 is pulled up into the accommodation section and past the stop blocks 54, the stop blocks 54 are rotated to an upright position in which the annular support ring 164 can be moved past the stop blocks. Next the stop blocks 54 are rotated around their respective horizontal axes 55 to their horizontal position which is shown in Fig 1B. The chain table 100 is then let down until its annular support ring 164 is supported on the stop blocks 54 which in turn are supported on the support platforms 56. Subsequently one or more wedges 57 are driven into the opening 51 between the turret 50 and the chain table 100 to further prevent movement of the chain table relative to the turret. Fig. 1B shows a human operator manually driving a wedge 57 into the opening 51. The operator inserts the wedge 51 between an inner edge of the said opening in the turret and a conical surface 161 of the chain table 100 by turning a wheel 59 which is connected to a spindle 58, which spindle in turn is attached to the wedge 57. Once the chain table 100 has been fixed to be stationary relative to the turret, the position and rotation of both the chain table and turret 50 relative to the sea bed is maintained by the anchor lines 80 which are connected to the body 110 of the chain table 100. In order to further strengthen the connection the chain table may be permanently fixed to the turret by means of welds and/or bolts or the like.

[0042] In Fig. 1B the chain table 100 and its connections to the anchor lines 81,82,83 and to the turret 50 are illustrated in greater detail. The chain table 100 comprises a substantially cylindrical main body 110 arranged outside of the accommodation space 53 of the turret and on a side of the bottom side 52 of the turret which faces the sea bed. The main body 110 comprises an outer surface 113 which extends between the bottom surface 111 and a circumferential top edge 112 of the body. At the circumferential top edge 112 the body merges into the insertion end 160 which comprises a conical portion 162 which tapers towards the longitudinal axis L in a direction away from the main body 110. The conical portion 162 is adapted for facilitating alignment of the insertion end 160 into the accommodation space 53, in particular while the insertion end is being moved through the opening 51. At the bottom side 51 guide members 61 are provided which transition from the opening 51 in the bottom side 52 of the turret towards to sea bed and away from the vertical axis of rotation V. When the insertion end 160 of the chain table 100 is pulled up into the accommodation space 53 sliding contact of the conical portion 162 of the insertion end 160 over the guide members 61 provides a rough alignment of the insertion end into the accommodation space.

[0043] Between the bottom surface 111 and the top edge 112 a plurality of connectors 131,132,133 is provided which is partitioned into different sets of connectors arranged at different heights h1, h2, h3 along the longitudinal axis L of the main body 110. Though only one such connector 131,132,133 is shown for each set, it will be clear that each set comprises multiple such connectors in order to balance forces exerted by the anchor lines on the chain table. In the embodiment of Fig. 1B, each set has three connectors spaced equidistantly along the circumference of the outer surface 113. Corresponding connectors of the different sets are arranged on the main body 110 in rows along lines parallel to the longitudinal axis L. In this manner space for passage of one or more riser conduits 71,72 is available between neighbouring rows of connectors.

[0044] Fig. 1C schematically shows a view of the same chain table 100 of Figs. 1A and 1B, again with only three of the plurality of connectors shown for reasons of clarity. Instead of being attached to a turret, the chain table shown in Fig. 1C is supported by the sea bed B via a pedestal 300 having an end 301 which embedded in the sea bed B. The main body of the chain table 110 comprises substantially solid steel annular rings 121, 122,123. The rings are attached with their outer circumference to the outer surface 113 of the main body 110. On their inner circumference the rings are attached to an inner cylindrical surface 114 of the main body, which inner cylindrical surface defines a hollow interior 115 of the chain table. When the chain table 100 is submerged beneath the water surface water can flow freely into and out of the interior 115 through the connectors 131, 132, 133 which form openings in the outer surface 113, openings 125 in the inner surface 114, openings 126 in the conical portion 162, and opening 127 in annular ring 163 of the insertion end 160. The openings ensure that the chain table remains free from confined pockets of air, i.e. from pockets of which cannot escape the from chain table when it is lowered to the sea bed, allowing the chain table to be used at any depth without modification.

[0045] The pedestal 300 vertically spaces the chain table 100 apart from the sea bed and prevents the chain table from being partially or completely buried in the soil when it is left for prolonged periods of time (e.g. at least two weeks) on the pedestal 300 and while soil may shift due to sea currents. The pedestal 300 comprises three upright supports, two of which 311, 312 are shown in Fig. 1C, and between which the outer surface 113 of the body 110 of the chain table 100 is held in an upright position while chain table rests with its bottom surface 112 on annular support surface 302 of the pedestal 300. A notch 316 in upright support 312 is adapted for cooperating with a cam 116 on the body of the chain table to keep the chain table in a rotationally determined orientation while it is supported on the pedestal 300. When the chain table is supported on the pedestal thus both the position and rotational orientation of the chain table with respect to the pedestal are substantially fixed, facilitating connecting of anchor line ends to the chain table.

[0046] In Fig. 1C only anchor line 81 is shown to be connected to the chain table. The anchor line 81 is connected to a rigid arm 181 which in turn is connected via hinges p1, p2 to a coupling 140 which has been inserted into connector bush 131. The coupling 140 comprises a spherical distal end 141 having a first diameter and which merges into a section 142 having a second, smaller diameter. The section 142 merges into the base 143 of the coupling which is dimensioned for being supported in the bush and making contact with the bush along a circumference of the base 143.

[0047] With the coupling 140 having been inserted in the connector 131 at height h1, anchor line 82, which is arranged spaced apart from the chain table and supported directly on the sea bed B, can be connected to the connector 132 at height h2. This is done by pulling a haul-in line 10 which is connected to the coupling 140 at the end of rigid arm 182 and which runs through connector 132 and opening 126 to a haul in mechanism on a vessel. By hauling in the line 10, the coupling 140 attached to the anchor line 82 is pulled into connector 132 and the spherical distal end 141 of the coupling causes latch 146 to rotate so that the spherical distal end passes beyond the latch. The latch 146 is provided with recess having a diameter smaller than that the spherical end but larger than the diameter of section 142 of the coupling. During pulling in of the haul-in line, the spherical end continues to push against the latch until the recess in the latch slides past the spherical end and over portion 142. Subsequently the tension on haul-in line 10 is released, causing the coupling 140 connected thereto to slide, due to gravity, back towards the sea bed until the spherical end 141 contacts the edges of the recess of the latch and is held in place thereby.

[0048] Preferably, each anchor line coupling 140 of the plurality of anchor lines 81,82,83 is connected to corresponding connector 131, 132, 133 after anchor line couplings have already been inserted in the connectors higher levels in a same row of connectors. This reduces the risk of the anchor line couplings becoming tangled. Anchor line couplings would thus first be pulled into the connectors of a row in the set at height h1 furthest from the sea bed, next anchor line couplings would be pulled into the connectors of said row in the set at height h2 which is second furthest from the sea bed, and last anchor line couplings would be pulled into the connectors of said row in the set at height h3 closest to the sea bed. When there is no turret and/or vessel within the vicinity of the chain table that is supported on the sea bed, ends of the haul-in lines opposite from the ends connected to the anchor chain ends may be attached to marking buoys which float in the vicinity of the chain table, preferably on the water surface, for easy retrieval of the haul in lines.

[0049] Fig. 2A shows a vessel 1' with a chain table 200 according to a second embodiment of the invention attached thereto. A turret 50' having an opening 51'at its bottom side 51' is arranged in a moonpool 2' of the vessel. A cable 9' is connected to the chain table 200 and runs, via a guide wheel 6' to a haul in mechanism 8', here in the form of a winch, wherein the haul-in mechanism is arranged on a deck 5'of the vessel. As before, the vessel 1' is adapted to weathervane around a vertical axis V which coincides with a longitudinal axis of the chain table 200. The insertion end 260 of the chain table 200 is similar to the insertion end 160 of the chain table 100 shown in Figs. 1A-1C. However, the connectors of the main body 210 of the chain table 200 each comprise rigid arms 285,286 hingeably and fixedly connected the chain table 200. Each of the arms 285, 286 in turn is connected to a corresponding anchor line 85, 86. Though only two rigid arms and corresponding anchor lines are shown, it will be clear that multiple connectors are provided in different sets at different heights along the longitudinal axis L of the chain table, each connector comprising a corresponding arm.

[0050] When the chain table 200 is not attached to the turret 50' in the moonpool 2' of the vessel 1' and is initially sunk to the bottom of the sea bed, the rigid arms 285, 286 for connection to the anchor lines 85, 86 are already attached to the chain table. Generally, prior to letting the chain table sink to the sea bed, no anchor lines be attached to the chain table. Once the chain table has finished sinking and the bottom surface of the chain table is supported on the sea bed, each of the arms may be connected to a corresponding end of and anchor line which has preferably already been anchored to the sea bed at its other end. Alternatively, a part or all of the anchor lines may be connected to the rigid arms before letting the chain table sink to the sea bed, and once the chain table has finished sinking and is supported on the sea bed the other ends of the anchor lines may be anchored to the sea bed.

[0051] Fig. 2B shows a cross-sectional view of the chain table of Fig 2A supported with the bottom surface of its body 210 on the support surface 302 of pedestal 300 on the sea bed B. Similar to the chain table 100 of Fig. 1B, the body 210 of the chain table 200 comprises an outer surface 214 and an inner surface 213 which defines an hollow interior 215 that is freely accessible to water, e.g. through openings in the outer surface (not shown). A row of connectors 231, 232, 233 with hingeably connected arms 281,282,283 is provided along the main body 210 and extends parallel to the longitudinal axis L of the chain table. For reasons of clarity only one such row is shown, though the chain table 200 typically will have three such rows spaced equidistantly around the circumference of the outer surface. Each of the rigid arms is connected to the outer surface of the chain table 200 via a hinge with a first axis of rotation in a plane normal to the longitudinal axis, wherein this hinge in turn is connected to a further hinge with an second axis of rotation perpendicular to the first axis of rotation, wherein the further hinge is attached to the respective arm which forms an end of an anchor line. In order to keep the arms 281, 282, 283 at a non-zero angle to the longitudinal axis L stop plates 241,242,243,244 are provided which limit the extent to which each arm can rotate around the first axis of rotation. Especially during transport and installation of the chain table on the pedestal the stop plates substantially prevent movement of the rigid arms.

[0052] Fig. 3A shows an isometric view of a main body 410 of an embodiment of a chain table according to the present invention. Besides the main body 410 , the chain table may comprise an insertion end connected at the circumferential top edge 412 of the body. The body 410 comprises a circumferential outer surface 413 which extends between the top edge 413 and a bottom surface 411 of the body 410. For providing increased structural integrity, the main body further comprises an cylindrical inner surface 414 which defines a hollow interior 415 into and out of which water can freely flow, e.g. through openings 425 in the outer surface 413 and openings (not shown) in the inner surface 414. Three rows of connectors are arranged along the outer surface, as is shown more clearly with reference to Figs. 3B, 3C and 3D. Additionally, the body 410 is provided with air chamber 417 which is open ended at the bottom surface 411 and adapted for releasably trapping air therein. Just prior to hauling in the chain table while the chain table is supported with its bottom surface 411 on the sea bed, the air chamber 471 may be filled with gas, such as air, to provide additional buoyancy during hauling in of the chain table. As the chain table is moved away from the sea bed, the gas expands and a portion thereof can escape from the open end. Though not shown, the air chamber may extend along a substantial part of the body, e.g. along at least half the length of the body along the longitudinal axis L.

[0053] Fig. 3B, 3C and 3D respectively shows a cross-sectional view through the main body 410 at heights h1, h2, h3 wherein the rigid arms are shown and when the main body is placed on a pedestal 300 as described earlier herein, with the pedestal shown in dotted lines to indicate its location if the views had been cross-sectional side views. The figures show connectors in three rows, the first row comprising connectors 441a, 441b, 442a,442b and 443a, the second row comprising connectors 441c,441d, 442c,442d and 443b, and the third row comprising connectors 441e, 441f, 442e, 442f and 443c. The connectors from adjacent rows are spaced apart at their respective heights h1, h2, h3 by different angles γ1,γ2, and γ3. In the present case γ1>γ2>γ3, with γ1 substantially equal to 120 degrees, γ2 substantially equal to 112 degrees, and γ3 substantially equal to 104 degrees. However, as long as the connectors at different heights are arranged at different angles, contact between anchor lines connected to the chain table at the different heights can be substantially avoided, in particular once the chain table has been attached to a turret. The rigid arms 481a-481f which are part of the connectors at the first height h1 at shown as well, as are the rigid arms which are part of the connectors at the second height h2 and third height h3.

[0054] Fig. 4 schematically shows a portion of a vessel with a chain table according to a third embodiment of the invention. The chain table 500 has a main body 510, only part of which is shown and which may be similar or the same as the main body 110 or 210 shown in Figs. 1 and 2. The main body 510 merges into an insertion end 560 which has a conical portion 562 and which is accommodated in accommodation space 53" of the turret 50". An annular support ring 564 at the top of the insertion end 560 comprises a groove 566 into which rotatable locking arms 54" of the vessel protrude. Each of the locking arms 54" is rotatable into and out of the groove 566 around an associated vertical axis of rotation 55". Near the opening 51" in the bottom side 52" of the turret 50", the turret is provided with blocking members 57" which engage pads 568 at cylindrical portion 561 of the insertion end 560 during its motion under radial load and are adapted for blocking relative rotation between the turret 50" and the chain table. This ensures that the chain table 500, when fixed to the turret, has a rotational orientation relative to the turret 50", allowing risers to be connected to riser conduits which extend through the bottom side of the turret without the anchor lines obstructing access. Thus, the longitudinal axis L of the turret 50" and the longitudinal axis V of the moonpool of the vessel in which the turret is arranged coincide.

[0055] The present invention has been described above with reference to a number of exemplary embodiments as shown in the drawings. Modifications and alternative implementations of some parts or elements are possible, and are included in the scope of protection as defined in the appended claims.

Claims

1. Chain table (100; 200; 400) for a turret (50; 250;450) of a vessel (1; 1') floating in the sea, wherein said turret is adapted to rotate in a moonpool (2) of the vessel (1), said chain table comprising a main body (110; 210; 410) with a bottom surface (111; 211), a circumferential top edge (112; 212), an outer surface (113; 213) extending therebetween around a longitudinal axis (L) of the main body (110; 210), and a plurality of connectors (131a-c, 132a-c; 213a-c, 232a-c) arranged along said outer surface (113'213) and adapted for connecting to an end of an anchor line (81,82,83,85, 86)
characterized in that said plurality of connectors is partitioned into different sets of connectors, wherein each set is arranged at a height (h1,h2,h3) along said longitudinal axis (L) that differs from the height of the other sets and is spaced apart from said bottom surface (111; 211),
wherein said chain table (100; 200; 400) is adapted for sinking to the sea bed and is further adapted for attachment to the turret with said longitudinal (L) axis extending substantially vertically.

2. Chain table according to claim 1, wherein the chain table has an elongated shape extending along the longitudinal axis (L) of the body, and wherein the chain table is adapted, when supported by the sea bed, to be supported substantially completely on its bottom surface (111; 211) in such a manner that said longitudinal axis (L) is substantially vertical, with the connectors (131a-c, 132a-c; 213a-c, 232a-c) spaced apart from said bottom surface.

3. Chain table according to claim 1 or 2, wherein each of said connectors is arranged on the body in a row, each row comprising one or more connectors from each set, wherein, when viewed in projection on a plane perpendicular to the longitudinal axis, the connectors in each row are spaced at an angular distance of at least 90 degrees from connectors in adjacent rows, preferably at least 110 degrees.

4. Chain table according to any one of the preceding claims, wherein each of said connectors comprises a substantially rigid arm (181-183; 281-283) having a proximate end pivotably connected to said body at a position radially spaced apart from the longitudinal axis (L) and having a distal end adapted for connection to an anchor line (81-83; 85;86) .

5. Chain table according to claim 4, wherein said arms (181-183; 281-283) are arranged to allow one or more of said risers to pass between neighboring arms in each set on an outer side of said outer surface (113; 213).

6. Chain table according to any one of the preceding claims, wherein said body (10) comprises a hollow interior (115; 215) defined by said bottom surface (111;211) and outer surface (113;213), wherein the chain table is provided with a number of through openings (125, 126, 127, 131a-c, 132a-c; 225, 227, 231a-c,232a-c) for allowing substantially free passage of water into and out of said interior from an outer surface of said chain table when the body (110; 210) is submerged in the water, preferably wherein said hollow interior extends along said longitudinal axis at least over the height between the set of connectors closest to the top surface and the set of connectors closest to the bottom surface.

7. Chain table according to any one of the preceding claims, wherein the body is provided with an air chamber (417) which is open-ended at the bottom surface (411) of the body (410) and adapted to be filled with air.

8. Chain table according to any one of the preceding claims, wherein said chain table (100; 200; 400) is free from riser conduits.

9. Anchoring system comprising a chain table according to any one of the preceding claims, further comprising:
a pedestal (300) having a lower end (301) which extends partially into the sea bed and support surface (302) adapted for supporting the bottom surface (111; 211) of said chain table thereon (100; 200), preferably wherein the pedestal is provided with upright supports (311,312,313) which extend to a level above the support surface and are adapted for holding the outer surface (113; 213) of the body (110; 210) of the chain table (100; 200) therebetween in an upright position while the chain table rests with its bottom surface (112; 212) on said support surface (302).

10. A vessel (1; 1') which floats in the sea and comprises a moonpool (2), a turret and a chain table according to any one of claims 1-8, wherein the turret (50; 250) is rotatably supported in the moonpool, wherein said turret, at its bottom side (52; 252; 452), is provided with an opening (51; 251; 451) which debauches into an accommodation space (53; 253; 453) for at least partially accommodating said chain table, wherein said vessel is provided with a cable haul in mechanism adapted for hauling in a cable attached to the chain table in order to lift said chain table from the sea bed and into the accommodation space of said turret.

11. Vessel according to claim 10, wherein the turret is provided with a plurality of riser connectors which are arranged around the opening (51; 251; 451) at its bottom side.

12. Vessel according to any one of claims 10-11, wherein said circumferential outer surface has a maximum outer diameter which is less than an inner diameter of the moonpool at the bottom surface of the turret, preferably wherein said maximum outer diameter is less than, or less than half, an outer diameter of the bottom side of the turret.

13. Method of attaching a chain table (100; 200; 400) to a turret that is rotatably supported in a moonpool of a vessel (1; 1') in an area where one or more risers are provided for transporting hydrocarbons from the sea bed to the turret, said method comprising the steps of:

• during an first stage during which said vessel is not in the neighbourhood of said area:

- attaching a plurality of anchor lines with their first ends to the sea bed in said area;

- letting a chain table (100; 200; 400) sink to the sea bed in said area, wherein said chain table has a longitudinal axis (L) and a bottom surface (111; 211) and is provided with a plurality of connectors which are partitioned into different sets of connectors, wherein each set is arranged at a height (h1,h2,h3) along said longitudinal axis (L) that differs from the height of the other sets and is spaced apart from said bottom surface (111; 211);

• during a second stage during which said vessel is in the neighbourhood of said area:

- positioning said vessel (1, 1') with its moonpool substantially above the chain table;

- pulling said chain table and the plurality of anchor lines connected thereto up towards the turret until the chain table is partially accommodated in the accommodation space of said turret;

- fixing said chain table to the turret and subsequently connecting the risers to the turret at a position of the turret spaced apart from the chain table.

14. Method according to claim 13, further comprising, during the first stage and prior to letting the chain table sink to the sea bed, installing a pedestal (300) on the sea bed, wherein said pedestal is adapted for supporting the bottom surface (111; 211) of the chain table thereon, and wherein letting the chain table sink to the sea bed comprises letting the chain table sink until its bottom surface is supported by the sea bed via the pedestal.

15. Method according to claim 13 or 14, further comprising, when said chain table has sunk to the sea bed and is supported on its bottom surface, attaching a second end of each anchor line to the chain table by pulling said second end into a connector of said plurality of connectors using a haul- in line connected to said second end, wherein the pulling in is achieved by hauling in the haul-in line using a haul-in mechanism that is arranged on the vessel.

Ansprüche

1. Kettenplatte (100; 200; 400) für einen Drehturm (50; 250; 450) eines im Meer schwimmenden Schiffs (1; 1'), wobei der Drehturm angepasst ist, sich in einem Moonpool (2) des Schiffs (1) zu drehen, wobei die Kettenplatte einen Hauptkörper (110; 210; 410) mit einer Bodenfläche (111; 211), eine umlaufende Oberkante (112; 212), eine Außenfläche (113; 213), die sich dazwischen um eine Längsache (L) des Hauptkörpers (112; 210) erstreckt, und eine Vielzahl von Anschlussstücken (131a-c, 132a-c; 213a-c, 231a-c) umfasst, die entlang der Außenfläche (113; 213) angeordnet sind und angepasst sind, mit einem Ende einer Ankerleine (81, 82, 83, 85, 86) verbunden zu werden,

dadurch gekennzeichnet, dass die Vielzahl von Anschlussstücken in verschiedene Sätze von Anschlussstücken unterteilt ist, wobei jeder Satz in einer Höhe (h1, h2, h3) entlang der Längsachse (L) angeordnet ist, die sich von der Höhe der anderen Sätze unterscheidet und auf Abstand zu der Bodenfläche (111; 211) liegt,

wobei die Kettenplatte (100; 200; 400) zum Absinken auf den Meeresboden angepasst ist, und ferner zur Befestigung am Drehturm mit sich im Wesentlichen vertikal erstreckender Längsachse (L) angepasst ist.

2. Kettenplatte nach Anspruch 1, wobei die Kettenplatte eine längliche Form hat, die sich entlang der Längsachse (L) des Körpers erstreckt, und wobei die Kettenplatte angepasst ist, wenn sie auf dem Meeresboden aufliegt, im Wesentlichen vollständig auf ihrer Bodenfläche (111; 211) aufzuliegen, so dass die Längsachse (L) im Wesentlichen vertikal ist, wobei die Anschlussstücke (131a-c, 132a-c; 213a-c, 232a-c) auf Abstand zur Bodenfläche liegen.

3. Kettenplatte nach Anspruch 1 oder 2, wobei jedes der Anschlussstücke in einer Reihe an dem Körper angeordnet ist, wobei jede Reihe ein oder mehrere Anschlussstücke von jedem Satz von Anschlussstücken umfasst, wobei, bei Betrachtung in Projektion auf eine senkrecht zur Längsachse stehenden Ebene, die Anschlussstücke in jeder Reihe einen Winkelabstand zu den Anschlussstücken der benachbarten Reihen von mindestens 90 Grad, vorzugsweise mindestens 110 Grad, haben.

4. Kettenplatte nach einem der vorhergehenden Ansprüche, wobei jedes der Anschlussstücke einen im Wesentlichen starren Arm (181-183; 281-283) umfasst, der ein proximales Ende, das schwenkbar an einer Stelle, die radial in einem gewissen Abstand zur Längsachse (L) steht, mit dem Körper verbunden ist, und ein distales Ende hat, das zur Verbindung mit einer Ankerleine (81-83; 85; 86) angepasst ist.

5. Kettenplatte nach Anspruch 4, wobei die Arme (181-183; 281-283) so angeordnet sind, dass es der einen oder den mehreren Steigleitungen ermöglicht ist, zwischen benachbarten Armen in jedem Satz von Anschlussstücken auf einer Außenseite der Außenfläche (113; 213) zu verlaufen.

6. Kettenplatte nach einem der vorhergehenden Ansprüche, wobei der Körper (10) einen hohlen Innenraum (115; 215), der durch die Bodenfläche und die Außenfläche (113; 213) definiert wird, umfasst, wobei die Kettenplatte mit einer Anzahl von Durchgangsöffnungen (125, 126, 127, 131a-c, 132a-c, 225, 227, 231a-c, 232a-c) versehen ist, um einen im Wesentlichen freien Wasserdurchtritt in und aus dem Innenraum von einer Außenfläche der Kettenplatte zu ermöglichen, wenn der Körper (110; 210) in Wasser eingetaucht ist, vorzugsweise wobei der hohle Innenraum sich entlang der Längsachse mindestens über die Höhe zwischen dem Satz von Anschlussstücken, der sich am nächsten an der Deckfläche befindet, und dem Satz von Anschlussstücken, der sich am nächsten an der Bodenfläche befindet, erstreckt.

7. Kettenplatte nach einem der vorhergehenden Ansprüche, wobei der Körper mit einer Luftkammer (417) ausgestattet ist, die an der Bodenfläche (411) des Körpers (410) offen ist und angepasst ist, mit Luft gefüllt zu werden.

8. Kettenplatte nach einem der vorhergehenden Ansprüche, wobei die Kettenplatte (100; 200; 400) frei von Steigleitungen ist.

9. Ankersystem umfassend eine Kettenplatte nach einem der vorhergehenden Ansprüche, weiter umfassend:
einen Sockel (300) mit einem unteren Ende (301), das sich teilweise in den Meeresboden erstreckt, und mit einer Stützfläche (302), die angepasst ist, die Bodenfläche (111; 211) der Kettenplatte (100; 200) darauf zu tragen, wobei der Sockel vorzugsweise mit aufrecht stehenden Stützen (311, 312, 313) ausgestattet ist, die sich bis auf eine Höhe über die Stützfläche erstecken und angepasst sind, die Außenfläche (113; 213) des Körpers (110; 210) der Kettenplatte (100; 200) dazwischen in einer aufrechten Stellung zu halten, während die Kettenplatte mit ihrer Bodenfläche (112; 212) auf der Stützfläche (302) ruht.

10. Schiff (1; 1'), das im Meer schwimmt und einen Moonpool (2), einen Drehturm und eine Kettenplatte nach einem der vorhergehenden Ansprüche 1-8 umfasst, wobei der Drehturm (50; 250) drehbar im Moonpool gelagert ist, wobei der Drehturm an seiner Bodenseite (52; 252; 452) mit einer Öffnung (51; 251; 451) ausgestattet ist, die in einen Aufnahmeraum (53; 253; 453) für eine zumindest teilweise Unterbringung der Kettenplatte führt,
wobei das Schiff mit einem Mechanismus zum Seileinziehen ausgestattet ist, um ein Seil, das an der Kettenplatte angebracht ist, einzuziehen, um die Kettenplatte vom Meeresboden in den Aufnahmeraum des Drehturms hochzuheben.

11. Schiff nach Anspruch 10, wobei der Drehturm mit einer Vielzahl von Steigleitungsverbindungen ausgestattet ist, die um die Öffnung (51; 251; 451) an der Bodenseite herum angeordnet sind.

12. Schiff nach einem der Ansprüche 10-11, wobei die umlaufende Außenfläche einen maximalen Außendurchmesser hat, der kleiner als ein Innendurchmesser des Moonpools an der Bodenfläche des Drehturms ist, wobei der maximale Außendurchmesser vorzugsweise kleiner ist als ein Außendurchmesser der Bodenseite des Drehturms oder kleiner ist als die Hälfte eines Außendurchmessers der Bodenseite des Drehturms.

13. Verfahren zur Befestigung einer Kettenplatte (100; 200; 400) an einen Drehturm, der drehbar in einem Moonpool eines Schiffs (1; 1') gelagert ist, das in einem Bereich liegt, wo eine oder mehrere Steigleitungen vorhanden sind, um Kohlenwasserstoff vom Meeresboden in den Drehturm zu transportieren, wobei das Verfahren folgende Schritte umfasst:

• während einer ersten Stufe, während der das Schiff noch nicht in der Nähe des Bereichs ist:

- Befestigen einer Vielzahl von Ankerleinen mit ihren ersten Enden am Meeresboden in dem Bereich;

- Absenken einer Kettenplatte (100; 200; 400) auf den Meeresboden in diesem Bereich, wobei die Kettenplatte eine Längsachse (L) und eine Bodenfläche (111; 211) aufweist und mit einer Vielzahl von Anschlussstücken ausgestattet ist, die in verschiedene Sätze von Anschlussstücken unterteilt ist, wobei jeder Satz in einer Höhe (h1, h2, h3) entlang der Längsachse (L) angeordnet ist, die sich von der Höhe der anderen Sätze unterscheidet und auf Abstand zu der Bodenfläche (111; 211) liegt;

• während einer zweiten Stufe, während der das Schiff in der Nähe des Bereichs ist:

- Positionieren des Schiffs (1, 1') mit seinem Moonpool im Wesentlichen über der Kettenplatte;

- Ziehen der Kettenplatte und der daran verbundenen Vielzahl von Ankerleinen nach oben zum Drehturm, bis die Kettenplatte teilweise in dem Aufnahmeraum des Drehturms untergebracht ist;

- Befestigen der Kettenplatte an dem Drehturm und nachfolgendes Befestigen der Steigleitungen am Drehturm an einer Stelle des Drehturms, die auf Abstand zur Kettenplatte liegt.

14. Verfahren nach Anspruch 13, weiter umfassend, dass, während der ersten Stufe und vor dem Absenken der Kettenplatte auf den Meeresboden, ein Sockel (300) am Meeresboden angebracht wird, wobei der Sockel angepasst ist, die Bodenfläche (111; 211) der Kettenplatte darauf zu tragen, und wobei das Absenken der Kettenplatte auf den Meeresboden beinhaltet, dass die Kettenplatte soweit abgesenkt wird, bis die Bodenfläche über den Sockel durch Meeresboden getragen wird.

15. Verfahren nach den Ansprüchen 13 oder 14, weiter umfassend, dass, wenn die Kettenplatte auf den Meeresboden abgesenkt ist und auf ihrer Bodenfläche ruht, ein zweites Ende von jeder Ankerleine an der Kettenplatte befestigt wird, indem das zweite Ende in ein Anschlussstück der Vielzahl von Anschlussstücken durch ein Schleppseil, das mit dem zweiten Ende verbunden ist, gezogen wird, wobei das Ziehen erreicht wird, indem das Schleppseil unter Verwendung eines Einziehmechanismus, der am Schiff angeordnet ist, eingezogen wird.

Revendications

1. Table à chaîne (100 ; 200 ; 400) pour une tourelle (50 ; 250 ; 450) d'un navire (1 ; 1') flottant sur la mer, ladite tourelle étant apte à tourner dans un puits central (2) du navire (1), ladite table à chaîne comprenant un corps principal (110 ; 210 ; 410) avec une surface inférieure (111 ; 211), un bord supérieur circonférentiel (112 ; 212), une surface externe (113 ; 213) s'étendant entre eux autour d'un axe longitudinal (L) du corps principal (110 ; 210), et une pluralité de connecteurs (131a-c, 132a-c ; 213a-c, 232a-c) disposés le long de ladite surface externe (113 ; 213) et aptes à se raccorder à une extrémité d'une ligne d'ancrage (81, 82, 83, 85, 86),
caractérisé par le fait que ladite pluralité de connecteurs est séparée en différents ensembles de connecteurs, chaque ensemble étant disposé à une hauteur (h1, h2, h3) le long dudit axe longitudinal (L) qui diffère de la hauteur des autres ensembles et étant espacé de ladite surface inférieure (111 ; 211),
ladite table à chaîne (100 ; 200 ; 400) étant apte à couler jusqu'au fond marin et étant en outre apte à être fixée à la tourelle avec ledit axe longitudinal (L) s'étendant sensiblement verticalement.

2. Table à chaîne selon la revendication 1, la table à chaîne ayant une forme allongée s'étendant le long de l'axe longitudinal (L) du corps, et la table à chaîne étant apte, lorsqu'elle est supportée par le fond marin, à être supportée sensiblement entièrement sur sa surface inférieure (111 ; 211) d'une manière telle que ledit axe longitudinal (L) est sensiblement vertical, avec les connecteurs (131a-c, 132a-c ; 213a-c, 232a-c) espacés de ladite surface inférieure.

3. Table à chaîne selon la revendication 1 ou 2, dans laquelle chacun desdits connecteurs est disposé sur le corps dans une rangée, chaque rangée comprenant un ou plusieurs connecteurs de chaque ensemble, lorsque vus en projection sur un plan perpendiculaire à l'axe longitudinal les connecteurs dans chaque rangée étant espacés d'une distance angulaire d'au moins 90 degrés des connecteurs dans des rangées adjacentes, de préférence d'au moins 110 degrés.

4. Table à chaîne selon l'une quelconque des revendications précédentes, dans laquelle chacun desdits connecteurs comprend un bras sensiblement rigide (181-183 ; 281-283) ayant une extrémité proximale reliée de manière pivotante audit corps à une position espacée radialement de l'axe longitudinal (L) et ayant une extrémité distale adaptée pour une liaison avec une ligne d'ancrage (81-83 ; 85 ; 86).

5. Table à chaîne selon la revendication 4, dans laquelle lesdits bras (181-183 ; 281-283) sont disposés pour permettre à une ou plusieurs desdites colonnes montantes de passer entre des bras voisins dans chaque ensemble sur un côté externe de ladite surface externe (113 ; 213).

6. Table de chaîne selon l'une quelconque des revendications précédentes, dans laquelle ledit corps (10) comprend un intérieur creux (115 ; 215) défini par ladite surface inférieure (111 ; 211) et ladite surface externe (113 ; 213), la table à chaîne comporte un nombre d'ouvertures traversantes (125, 126, 127, 131a-c, 132a-c ; 225, 227, 231a-c, 232a-c) pour permettre un passage sensiblement libre d'eau dans ledit et hors dudit intérieur à partir d'une surface externe de ladite table à chaîne lorsque le corps (110 ; 210) est immergé dans l'eau, de préférence ledit intérieur creux s'étendant le long dudit axe longitudinal au moins sur la hauteur entre l'ensemble de connecteurs le plus proche de la surface supérieure et l'ensemble de connecteurs le plus proche de la surface inférieure.

7. Table à chaîne selon l'une quelconque des revendications précédentes, dans laquelle le corps comporte une chambre à air (417) qui a une extrémité ouverte à la surface inférieure (411) du corps (410) et qui est apte à être remplie d'air.

8. Table à chaîne selon l'une quelconque des revendications précédentes, ladite table à chaîne (100 ; 200 ; 400) étant exempte de conduits de colonne montante.

9. Système d'ancrage comprenant une table de chaîne selon l'une quelconque des revendications précédentes, comprenant en outre :
un socle (300) ayant une extrémité inférieure (301) qui s'étend en partie dans le fond marin et une surface de support (302) apte à supporter la surface inférieure (111 ; 211) de ladite table à chaîne (100 ; 200) sur celle-ci, de préférence le socle comportant des supports verticaux (311, 312, 313) qui s'étendent jusqu'à un niveau au-dessus de la surface de support et qui sont aptes à maintenir la surface externe (113 ; 213) du corps (110 ; 210) de la table à chaîne (100 ; 200) entre eux dans une position verticale tandis que la table à chaîne repose avec sa surface inférieure (112 ; 212) sur ladite surface de support (302).

10. Navire (1 ; 1') qui flotte sur la mer et qui comprend un puits central (2), une tourelle et une table à chaîne selon l'une quelconque des revendications 1 à 8, dans lequel la tourelle (50 ; 250) est supportée de manière rotative dans le puits central, ladite tourelle, sur son côté inférieur (52 ; 252 ; 452), comportant une ouverture (51 ; 251 ; 451) qui débouche dans un espace de réception (53 ; 253 ; 453) pour recevoir au moins en partie ladite table à chaîne,
ledit navire comportant un mécanisme de halage de câble apte à haler un câble fixé à la table à chaîne afin de lever ladite table à chaîne du fond marin et dans l'espace de réception de ladite tourelle.

11. Navire selon la revendication 10, dans lequel la tourelle comporte une pluralité de connecteurs de colonne montante qui sont disposés autour de l'ouverture (51 ; 251 ; 451) sur son côté inférieur.

12. Navire selon l'une quelconque des revendications 10 et 11, dans lequel ladite surface externe circonférentielle a un diamètre externe maximal qui est inférieur à un diamètre interne du puits central au niveau de la surface inférieure de la tourelle, de préférence ledit diamètre externe maximal étant inférieur, ou inférieur à la moitié, à un diamètre externe, du côté inférieur de la tourelle.

13. Procédé de fixation d'une table à chaîne (100 ; 200 ; 400) à une tourelle qui est supportée de manière rotative dans un puits central d'un navire (1 ; 1') dans une zone où une ou plusieurs colonnes montantes sont disposées pour transporter des hydrocarbures à partir du fond marin jusqu'à la tourelle, ledit procédé comprenant les étapes suivantes :

• pendant un premier stade pendant lequel ledit navire ne se trouve pas dans le voisinage de ladite zone :

- fixer une pluralité de lignes d'ancrage avec leurs premières extrémités au fond marin dans ladite zone ;

- laisser une table à chaîne (100 ; 200 ; 400) couler jusqu'au fond marin dans ladite zone, ladite table à chaîne ayant un axe longitudinal (L) et une surface inférieure (111 ; 211) et comportant une pluralité de connecteurs qui sont séparés en différents ensembles de connecteurs, chaque ensemble étant disposé à une hauteur (h1, h2, h3) le long dudit axe longitudinal (L) qui diffère de la hauteur des autres ensembles et étant espacé de ladite surface inférieure (111 ; 211) ;

• pendant un second stade pendant lequel ledit navire se trouve dans le voisinage de ladite zone :

- positionner ledit navire (1 ; 1') avec son puits central sensiblement au-dessus de la table à chaîne ;

- tirer ladite table à chaîne et la pluralité de lignes d'ancrage reliées à celle-ci vers le haut en direction de la tourelle jusqu'à ce que la table à chaîne soit en partie reçue dans l'espace de réception de ladite tourelle ;

- fixer ladite table à chaîne à la tourelle, puis relier les colonnes montantes à la tourelle à une position de la tourelle espacée de la table à chaîne.

14. Procédé selon la revendication 13, comprenant en outre, pendant le premier stade et avant de laisser la table à chaîne couler jusqu'au fond marin, installer un socle (300) sur le fond marin, ledit socle étant apte à supporter la surface inférieure (111 ; 211) de la table à chaîne sur celui-ci, et laisser la table à chaîne couler jusqu'au fond marin comprend laisser la table à chaîne couler jusqu'à ce que sa surface inférieure soit supportée par le fond marin par l'intermédiaire du socle.

15. Procédé selon la revendication 13 ou 14, comprenant en outre, lorsque ladite table à chaîne a coulé jusqu'au fond marin et est supportée sur sa surface inférieure, fixer une seconde extrémité de chaque ligne d'ancrage à la table à chaîne en tirant ladite seconde extrémité dans un connecteur de ladite pluralité de connecteurs à l'aide d'une ligne de halage reliée à ladite seconde extrémité, la traction étant obtenue en halant la ligne de halage à l'aide d'un mécanisme de halage qui est disposé sur le navire.

Drawing