Lower bearing for a turret and vessel provided therewith

Abstract

A lower bearing (6) is presented for a turret (3) positioned in a moonpool (2) of a vessel (1) for a rotation around a turret rotation axis. The moonpool is provided with a casing (5) defining, at least at a level corresponding with the position of the lower bearing, a circumferential casing surface directed towards the turret rotation axis, whereas the turret (3), at least at said level corresponding with the position of the lower bearing, is provided with a circumferential turret surface directed away from the turret rotation axis. The lower bearing is positioned between the circumferential casing and turret surfaces and comprises a first series of separate inner bearing blocks (9) arranged side-by-side in a circumferential direction and each having an inner surface engaging the circumferential turret surface, as well as a second series of separate outer bearing blocks (11) arranged side-by-side in a circumferential direction and each having an outer surface engaging the circumferential casing surface. The inner bearing blocks (9) have an outer bearing surface and the outer bearing blocks (11) have an inner bearing surface, which outer and inner bearing surfaces engage each other in a sliding manner for allowing a rotation of the turret with respect to the moonpool.

Description

[0001] Lower bearing for a turret and vessel provided therewith

[0002] In a first aspect the present invention relates to a lower bearing for a turret positioned in a moonpool of a vessel for a rotation around a turret rotation axis , wherein the moonpool is provided with a casing defining, at least at a level corresponding with the position of the lower bearing, a circumferential casing surface directed towards the turret rotation axis , whereas the turret , at least at said level corresponding with the position of the lower bearing, is provided with a circumferential turret surface directed away from the turret rotation axis and wherein the lower bearing is positioned between the circumferential casing and turret surfaces .

[0003] It is noted that the circumferential casing surface , because being directed towards the turret rotation axis , defines an inner circumferential casing surface .

[0004] It is an obj ect of the present invention to provide an improved lower bearing of such a type .

[0005] In accordance with the present invention the lower bearing is characteri zed in that it comprises a first series of separate inner bearing blocks arranged side-by-side in a circumferential direction and each having an inner surface engaging the circumferential turret surface , as well as a second series of separate outer bearing blocks arranged side-by-side in a circumferential direction and each having an outer surface engaging the circumferential casing surface , further wherein the inner bearing blocks have an outer bearing surface and the outer bearing blocks have an inner bearing surface , which outer and inner bearing surfaces engage each other in a sliding manner for allowing a rotation of the turret with respect to the moonpool .

[0006] It is noted that the indication ' side-by-side ' does not exclude the possibility that adj acent bearing blocks are positioned at some distance from each other with a spacing therebetween . A main advantage of the use of a first series of separate inner bearing blocks (which, basically, define an inner bearing ring) as well as a second series of separate outer bearing blocks (which, basically, define an outer bearing ring cooperating with the inner bearing ring) is the ability to individually tailor the shape and / or position of the bearing blocks such as to allow an adaptation or fine- tuning of the center point and / or roundness of the bearing rings defined by the inner bearing blocks and / or the outer bearing blocks .

[0007] Preferably, the inner bearing blocks are locked against a relative circumferential movement with respect to the circumferential turret surface (which movement otherwise might occur as a result of friction due to the rotation of the turret with respect to the casing of the moonpool ) .

[0008] For example , this may be achieved by pretensioning the inner bearing blocks to the circumferential turret surface . This increases the friction between the inner surface of the inner bearing blocks and the circumferential turret surface ( such that this friction is higher than the friction between the inner and outer bearing blocks ) .

[0009] In one embodiment the inner bearing blocks are pretensioned by means of bolts extending substantially radially through holes in the inner bearing blocks and the circumferential turret surface , respectively . However, other ways of pretensioning the inner bearing blocks are conceivable as well .

[0010] The inner bearing blocks may be embodied in many ways . For example , the inner bearing blocks may be made of a non-conductive material and / or their outer bearing surface may be made of , or may be covered with, low friction additives and / or the circumferential turret surface may be provided with a layer providing a high friction surface and corrosion protection, for instance thermally sprayed aluminium ( TSA) and / or the outer bearing surface of the inner bearing blocks may be provided with chamfered edges and / or the inner bearing blocks may be machinable such as to provide each with an individual thickness in a radial direction .

[0011] The above-mentioned embodiments of the inner bearing blocks individually or in speci fic combinations may provide individual ones or combinations of at least the following advantages : preventing the formation of adverse galvanic ef fects ; avoiding stress concentrations ( for example in the outer bearing ring as defined by the outer bearing blocks ) ; of fering an improved fine-tuning of the center point and / or roundness of the bearing rings defined by the inner bearing blocks and / or the outer bearing blocks ; reducing costs ; reducing construction times ; reducing wear of the individual components of the lower bearing; improving frictional forces between the inner bearing block and the circumferential turret surface .

[0012] In yet another embodiment of the lower bearing also the outer bearing blocks are locked against a relative circumferential movement with respect to the circumferential casing surface (which otherwise might occur as a result of friction due to the rotation of the turret with respect to the casing of the moonpool ) .

[0013] Preferably, then, the circumferential casing surface comprises attached thereto a number of frames arranged side-by-side in a circumferential direction and each provided with through-openings , each for receiving an outer bearing block . Once received in such a through-opening, an outer bearing block is ef fectively locked against a relative circumferential movement with respect to the ( inner ) circumferential casing surface .

[0014] In one embodiment each frame is attached to and engages the circumferential casing surface at a level above the level of the outer bearing blocks and for its remainder is spaced from the circumferential casing surface , wherein the frame in a radial direction is suf ficiently flexible to allow a radial deformation under normal operational conditions of the lower bearing, whereas the frame in a circumferential direction is suf ficiently rigid to prevent a substantial circumferential deformation under normal operational conditions of the lower bearing .

[0015] The flexibility for allowing a radial deformation ensures that the outer bearing blocks will remain in a secure engagement with the ( inner ) circumferential casing surface , whereas the rigidity in a circumferential direction helps in locking the outer bearing blocks against said relative circumferential movement with respect to the circumferential casing surface .

[0016] For improving the positioning of the outer bearing blocks , in one embodiment each outer bearing block is clamped in a corresponding through-opening .

[0017] For example it is conceivable that each outer bearing block is provided with a clamping block which, such as by assemblies of threaded bolts and nuts , is movable relative to the outer bearing block .

[0018] Preferably, then, the clamping block is an upper clamping block which is movable vertically such as to clamp the outer bearing block between a lower and upper edge of the respective through-opening . In such an embodiment it further is conceivable that a lower face of the outer bearing block and an upper face of the clamping block as well as the lower and upper edges of the through-opening are inclined correspondingly such that a clamping force induces a movement of the outer bearing block towards the circumferential casing surface , which further helps in maintaining a firm ( frictional ) engagement between the ( inner ) circumferential casing surface and the outer surface of the outer bearing blocks .

[0019] The frames may be embodied in many ways . For example each frame may be provided with at least two through- openings and preferably may be provided with four through- openings arranged side-by-side in a circumferential direction and / or wherein each frame may be made of steel and / or wherein a lower edge of each through-opening may be provided with a layer providing a high friction surface and corrosion protection, for instance TSA and / or wherein the level where each frame is attached to and engages the circumferential casing surface may be a level with a low stress compared to the stress at the level of the outer bearing blocks .

[0020] The outer bearing blocks also may be embodied in many ways . For example the outer bearing blocks may be made of a non-conductive material and / or their inner bearing surface may be made of , or has bonded thereto , a stainless steel or Alloy 625 plate which preferably is provided with rounded corners and / or the circumferential casing surface may be provided with a layer providing a high friction surface and corrosion protection, for instance TSA and / or the inner bearing surface of the outer bearing blocks may be provided with chamfered edges and / or the outer bearing blocks may be machinable such as to provide each with an individual thickness in a radial direction . These embodiment may provide advantages similar to those mentioned before with respect to possible embodiments of the inner bearing blocks .

[0021] In a second aspect the present invention relates to a vessel comprising a moonpool having a casing and a turret positioned in said moonpool and mounted therein for a rotation around a turret rotation axis relative to said moonpool by means of an upper bearing and a lower bearing, wherein the lower bearing is embodied in accordance with the present invention .

[0022] Hereinafter the invention will be elucidated while referring to the drawings , in which :

[0023] Figure 1 schematically illustrates a cross section of a vessel with moonpool and turret ;

[0024] Figure 2 , at a smaller scale and also schematically, illustrates a top plan view of part of the vessel of figure 1 ;

[0025] Figure 3 shows part of a lower bearing as attached to the turret ;

[0026] Figure 4 shows an outer bearing block;

[0027] Figure 5 shows a frame for outer bearing blocks ;

[0028] Figure 6 shows an outer bearing block with clamping block;

[0029] Figure 7 shows clamping blocks mounted in a frame , and

[0030] Figure 8 shows part of an assembled lower bearing .

[0031] Referring to figure 1 , a vessel 1 is shown schematically in cross section . Within said vessel 1 a moonpool 2 is defined in which a turret 3 is positioned for a rotation around a turret rotation axis 4 . The moonpool 2 is provided with a casing 5 defining, at least at a level corresponding with the position of a lower bearing 6 , an ( inner ) circumferential casing surface 7 directed towards the turret rotation axis 4 . It is noted that the position of said circumferential casing surface 7 relative to the remainder of the casing 5 is only schematically indicated in figure 1 and thus may di f fer from the representation in figure 1 ( for example a position closer to the turret rotation axis 4 is conceivable too ) .

[0032] In a corresponding manner the turret 3 , again at least at said level corresponding with the position of the lower bearing 6 , is provided with an ( outer ) circumferential turret surface 8 directed away from the turret rotation axis 4 . It is noted that the position of said circumferential turret surface 8 relative to the remainder of the turret 3 is only schematically indicated in figure 1 and thus may di f fer from the representation in figure 1 ( for example a position further away from the turret rotation axis 4 is conceivable too ) .

[0033] The lower bearing 6 is positioned between the circumferential casing and turret surfaces 7 , 8 and comprises a first series of separate inner bearing blocks 9 arranged side-by-side in a circumferential direction and each having an inner surface 10 engaging the circumferential turret surface 8 , as well as a second series of separate outer bearing blocks 11 arranged side-by-side in a circumferential direction and each having an outer surface 12 engaging the circumferential casing surface 7 .

[0034] The inner bearing blocks 9 have an outer bearing surface 13 and the outer bearing blocks 11 have an inner bearing surface 14 , which outer and inner bearing surfaces 13 , 14 engage each other in a sliding manner for allowing a rotation of the turret 3 with respect to the moonpool 2 ( or the casing 5 ) . It is noted that in figures 1 and 2 for illustration purposes a spacing is shown between the outer bearing surface 13 and the inner bearing surface 14 ; in practice this spacing will be absent . Further, there may be a spacing between adj acent bearing blocks , for example between the outer bearing blocks 11 .

[0035] There generally also will be at least one upper bearing 15 between the turret 3 and the casing 5 ( or another part of the vessel 1 , such as a deck 16 ) .

[0036] Figure 2 schematically shows a top plan view illustrating the relative positions of the inner bearing blocks 9 and outer bearing blocks 11 .

[0037] Figure 3 shows part of the turret 3 with the inner bearing blocks 9 and illustrates a manner in which the inner bearing blocks 9 may be locked against a relative circumferential movement with respect to the circumferential turret surface 8 . Speci fically, in this embodiment , the inner bearing blocks 9 are pretensioned to the circumferential turret surface 8 by means of bolts 17 extending substantially radially through aligned holes (not illustrated in detail ) in the inner bearing blocks 9 and the circumferential turret surface 8 , respectively and cooperating with nuts 18 positioned in recesses 19 such as not to protrude from the outer bearing surface 13 .

[0038] In preferred embodiments of the lower bearing the inner bearing blocks 9 are made of a non-conductive material and / or their outer bearing surface 13 is made of , or is covered with, low friction additives and / or the circumferential turret surface 8 is provided with a layer providing a high friction surface and corrosion protection, for instance thermally sprayed aluminium ( TSA) and / or the outer bearing surface 13 of the inner bearing blocks 9 is provided with chamfered edges 20 and / or the inner bearing blocks 9 are machinable such as to provide each with an individual thickness in a radial direction . Figure 4 shows a possible embodiment of an outer bearing block 11 . It may be made of a non-conductive material and in one embodiment ( as illustrated) its inner bearing surface 14 is made of , or has bonded thereto , a stainless steel or Alloy 625 plate 21 (which then would define the inner bearing surface 14 ) which preferably is provided with rounded corners 22 . A hoisting eye 23 may be provided for handling the outer bearing block ( for example during as- sembling / disassembling the lower bearing 6 ) .

[0039] The manner in which the outer bearing blocks 11 are locked against a relative circumferential movement with respect to the circumferential casing surface 7 and are attached thereto will be explained while referring to figures 5-7 .

[0040] Figure 5 illustrates a frame 24 . The circumferential casing surface 7 comprises attached thereto ( in a manner to be described below) a number of such frames 24 arranged side-by-side in a circumferential direction C . Each frame 24 is provided with a number of through-openings 25 located side-by-side , each for receiving an outer bearing block 11 . Each frame 24 is attached to and engages the circumferential casing surface 7 at a level above the level of the outer bearing blocks 11 (when mounted in the through- openings 25 ) by members schematically indicated at 26 in figure 5 and for its remainder is spaced from the circumferential casing surface 7 .

[0041] The frame 24 in a radial direction R is suf ficiently flexible to allow a radial deformation / movement under normal operational conditions of the lower bearing 6 ( as allowed also by the spacing mentioned in the previous paragraph) , whereas the frame 24 in the circumferential direc- tion C is suf ficiently rigid to prevent a substantial circumferential deformation / movement under normal operational conditions of the lower bearing 6 .

[0042] In the illustrated embodiment each outer bearing block 11 is clamped in a corresponding through-opening 25 by means of an upper clamping block 27 ( see figures 6 and 7 ) which, such as by assemblies of threaded bolts 28 and nuts 29 , is movable vertically relative to the outer bearing block 11 such as to clamp the outer bearing block between a lower and upper edge of the respective through-opening 25 . Such assemblies may cooperate with a plate 30 . Items 31 in figure 6 illustrate cathodic protection blocks .

[0043] A lower face of the outer bearing block 11 and an upper face of the clamping block 27 as well as the lower and upper edges 33 , 34 of the through-opening 25 may be inclined correspondingly such that a clamping force of the clamping block 27 induces a movement of the outer bearing block 11 towards the circumferential casing surface 7 ( according to direction R in figure 5 ) .

[0044] In the illustrated embodiment each frame 24 is provided with four through-openings 25 arranged side-by-side in a circumferential direction . Each frame 24 may be made of steel and a lower edge 33 of each through-opening 25 may be provided with a layer providing a high friction surface and corrosion protection, for instance TSA. The level where each frame 24 is attached ( see 26 in figure 5 ) to and engages the circumferential casing surface 7 preferably is a level with a low stress compared to the stress at the ( lower ) level of the outer bearing blocks 11 .

[0045] The circumferential casing surface 7 also may be provided with a layer providing a high friction surface and corrosion protection, for instance TSA and the inner bearing surface 14 of the outer bearing blocks 11 may be provided with chamfered edges . Finally, the outer bearing blocks 11 may be machinable such as to provide each with an individual thickness in the radial direction R .

[0046] Figure 8 shows part of the assembled lower bearing 6 with the circumferential casing surface 7 , a frame 24 attached thereto having through-openings 25 and outer bearing blocks 11 clamped therein which are provided with a stainless steel or Alloy 625 plate 21 , as well as the turret 3 defining the circumferential turret surface 8 engaging one side ( inner surface 10 ) of the inner bearing blocks 9 which at an opposite side ( outer bearing surface 13 ) slidingly engage the plate 21 of the outer bearing block 11 (which defines the inner bearing surface 14 ) .

[0047] The invention is not limited to the embodiments described which may be varied widely within the scope of the invention as defined by the appending claims .

Claims

CLAIMS1 . Lower bearing for a turret positioned in a moonpool of a vessel for a rotation around a turret rotation axis , wherein the moonpool is provided with a casing defining, at least at a level corresponding with the position of the lower bearing, a circumferential casing surface directed towards the turret rotation axis , whereas the turret , at least at said level corresponding with the position of the lower bearing, is provided with a circumferential turret surface directed away from the turret rotation axis and wherein the lower bearing is positioned between the circumferential casing and turret surfaces , characterized in that the lower bearing comprises a first series of separate inner bearing blocks arranged side-by-side in a circumferential direction and each having an inner surface engaging the circumferential turret surface , as well as a second series of separate outer bearing blocks arranged side-by-side in a circumferential direction and each having an outer surface engaging the circumferential casing surface , further wherein the inner bearing blocks have an outer bearing surface and the outer bearing blocks have an inner bearing surface , which outer and inner bearing surfaces engage each other in a sliding manner for allowing a rotation of the turret with respect to the moonpool .2 . Lower bearing according to claim 1 , wherein the inner bearing blocks are locked against a relative circumferential movement with respect to the circumferential turret surface .3 . Lower bearing according to claim 2 , wherein the inner bearing blocks are pre-tensioned to the circumferential turret surface .4 . Lower bearing according to claim 3 , wherein the inner bearing blocks are pre-tensioned by means of bolts extending substantially radially through holes in the inner bearing blocks and the circumferential turret surface , respectively .5 . Lower bearing according to any of the previous claims , wherein the inner bearing blocks are made of a non-conductive material and / or wherein their outer bearing surface is made of , or is covered with, low friction additives and / or wherein the circumferential turret surface is provided with a layer providing a high friction surface and corrosion protection, for instance thermally sprayed aluminium ( TSA) and / or wherein the outer bearing surface of the inner bearing blocks is provided with chamfered edges and / or wherein the inner bearing blocks are machinable such as to provide each with an individual thickness in a radial direction .6 . Lower bearing according to any of the previous claims , wherein the outer bearing blocks are locked against a relative circumferential movement with respect to the circumferential casing surface .7 . Lower bearing according to claim 6 , wherein the circumferential casing surface comprises attached thereto a number of frames arranged side-by-side in a circumferential direction and each provided with through-openings , each for receiving an outer bearing block .8 . Lower bearing according to claim 7 , wherein each frame is attached to and engages the circumferential casing surface at a level above the level of the outer bearing blocks and for its remainder is spaced from the circumferential casing surface , and wherein the frame in a radial direction is suf ficiently flexible to allow a radial deformation under normal operational conditions of the lowerbearing, whereas the frame in a circumferential direction is suf ficiently rigid to prevent a substantial circumferential deformation under normal operational conditions of the lower bearing .9 . Lower bearing according to claim 7 or 8 , wherein each outer bearing block is clamped in a corresponding through-opening .10 . Lower bearing according to claim 9 , wherein each outer bearing block is provided with a clamping block which, such as by assemblies of threaded bolts and nuts , is movable relative to the outer bearing block .11 . Lower bearing according to claim 10 , wherein the clamping block is an upper clamping block which is movable vertically such as to clamp the outer bearing block between a lower and upper edge of the respective through-opening .12 . Lower bearing according to claim 11 , wherein a lower face of the outer bearing block and an upper face of the clamping block as well as the lower and upper edges of the through-opening are inclined correspondingly such that a clamping force induces a movement of the outer bearing block towards the circumferential casing surface .13 . Lower bearing according to any of the claims 7- 12 , wherein each frame is provided with at least two through-openings and preferably is provided with four through-openings arranged side-by-side in a circumferential direction and / or wherein each frame is made of steel and / or wherein a lower edge of each through-opening is provided with a layer providing a high friction surface and corrosion protection, for instance TSA and / or wherein the level where each frame is attached to and engages the circumferential casing surface is a level with a low stress compared to the stress at the level of the outer bearing blocks .14 . Lower bearing according to any of the previous claims , wherein the outer bearing blocks are made of a non-conductive material and / or wherein their inner bearing surface is made of , or has bonded thereto , a stainless steel or Alloy 625 plate which preferably is provided with rounded corners and / or wherein the circumferential casing surface is provided with a layer providing a high friction surface and corrosion protection, for instance TSA and / or wherein the inner bearing surface of the outer bearing blocks is pro- vided with chamfered edges and / or wherein the outer bearing blocks are machinable such as to provide each with an individual thickness in a radial direction .15 . Vessel comprising a moonpool having a casing and a turret positioned in said moonpool and mounted therein for a rotation around a turret rotation axis relative to said moonpool by means of an upper bearing and a lower bearing, wherein the lower bearing is embodied in accordance with any of the previous claims .

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