GB2232946A - Device for tensioning multiple anchor chains - Google Patents

Abstract

A tensioning device for multiple anchor chains has a central axis 4 which is substantially vertical in use, a plurality of passages 3 for a respective anchor chain 17, 18, the passages being distributed about the central axis and having guiding surfaces 8 for the transition of the chain between the anchor end B and a vertical extending portion A, and blocking means or cam 15 associated with each passage to secure the chain against movement relative to the device in the direction of the anchor. An eye 5 provides for the attachment of a hoisting line (not shown) whereby a vertical force may be exerted on the device to apply tension to the anchor chains and an eye 14 provides for the attachment of a ballast weight. The device may be used in the anchoring of a tension leg platform or a buoy. <IMAGE>

Description

anchor line tensioning device and method for use thereof The invention relates to a tensioning device for passing through and tensioning at least one anchor line and to the thereby having penetrate into a mooring bed one or more anchors connected to one end of the anchor line, comprising at least one passing means for passage through the tensioning device of the anchor line, the passing means comprising guiding surfaces for guiding the anchor line, during use in a substantially vertical plane, and at least z blocking means associated with the passing means, with which relative movement of the tensioning device along the anchor line, in a direction from the anchor, can be prevented.The invention furthermore relates to a method for using such a tensioning device.

A tensioning device of the kind mentioned in the preamble is known from Dutch patent application 81 05294, describing a tensioning device through which during use of the tensioning device a first anchor line connected to a first anchor can be passed under trans it ion of a substantially horizontal extension towards a substantially vertical extension of that anchor line, the tensioning device being provided outside the curve in the path of the first anchor line with one or more attachment points for secondary anchor lines to be laid out as opposing line for the first anchor line. The tensioning device can move along the first anchor line towards the first anchor all the time, but movement in the opposite direction can be prevented by means of the blocking means.Zn use, the tensioning device is lowered along the anchor line to the vicinity of the mooring bed, whereafter a pulling force exerted on the other end of the first anchor line upon blocking engagement of the first anchor line with the blocking means ensures that the tensioning device is pulled up along and hence the first anchor line and the opposing secondary anchor line(s) are/is tensioned, with the result that the anchors connected therewith penetrate in the mooring bed and approach eacb other to some extent. By paying out again, the other end of the first anchor line the tensioning device will move downward again along the first anchor line, whereafter the operation described above is carried out again. This is being repeated several times.The great advantage hereby is that due to the fact that the tensioning device can be brought in a position near the mooring bed, the pulling forces exerted on the other md.of the first anchor line are converted into substantially horizontal pulling forces on the anchors, which as a result better penetrate the mooring bed. Zn order to reach a same grade of penetration of the anchors a smaller force is needed to pull, compared to pulling an anchor line running between the anchor and the pull end according to a cetenary.

Zn principle, the known tensioning device is meant for tensioning one anchor line Xt is possible that the secondary anchor line(s) and the first anchor line form the anchorage of a Single Point Mooring System (8PH) but only if the positioning tolerances of the object to be anchored allow this, in view of the possible movement in horizontal direction of a tensioning device during tensioning due to the fixed length of the secondary anchor line(s). Furthermore, when used in a SPM, with the known tensioning device only two or three anchor lines can be tensioned against each other, in case a situation is desired wherein the forces in the secondary anchor line(s) and that part of the first anchor line substantially extending horizontally will be substantially equal.

A main object of the invention is to provide a tensioning device of the kind indicated in the preamble, with which a solution is offered for the mentioned imperfections of the known tensioning device.

This object ia achieved in that the tensioning device comprises a central axis which during use of the tensioning device is substantially oriented vertically, and in that the tensioning device furthermore comprises a plurality of passing means for a associated number of anchor lines, the passing means being distributed about the central axis, the guiding surfaces of each passing means comprising facing portions substantially facing associated parts of guiding surfaces of one or more other passing means, as well as connecting means for connection of the tensioning device to at least one hoisting line, in order to exert a vertical force on the tensioning device during use.

because of the connecting means it is possible to pull the tensioning device up during uce and hence to tension a plurality of anchor lines passed through the tensioning device against each other, as the forces exerted by the anchor lines on the tensfoning device when the tensioning Cevice is being pulled can come in horizontal balance due to the indicated orientation of the portions of the guiding surfaces. In addition, because according to the invention the tensioning can be pulled up by means of ono or more separate hoisting lines in stead of by means of one of the anchor lines, the possibility is created to tension a lot of anchor lines against ach other at a comparable tension.

The tensioning device is preferably realized such that the blocking means associated with each passing means is arranged such that this blocking means and the associated anchor line can be brought in blocking engagement with each other if necessary but otherwise allow free passage of the anchor line across the guiding surf aces in two opposite directions. This embodiment is especially useful for anchoring systems, wherein it is desirable to tension a plurality of sets of opposing anchor lines to be tensioned against each other, in a successive manner.As the anchor lines now can be brought in or out of engagement with the blocking means as desired, the tensioning device can move freely over the anchor lines tensioned before, in two opposite directions, with the result that a successive set of anchor lines to be tensioned against each other can be tensioned without being influenced by the anchor lines tensioned before but now slack. Thus, the pulling forces exerted are divided over a limited number of anchor lines, so that large forces can be created in the anchor lines.

Each blocking means could in the sald preferred embodiment of tensioning device according to the invention be situated in the guiding surfaces and such that control means would be provided for having the blocking means protrude from the guiding surfaces in order te bring it into engagement with the anchor line passed therealong. The blocking means could also be integrated in the guiding surfaces in a fixed way, wherein the passing means should provide room for passing of the anchor line in two opposite directions out of blocking engangement with the blocking means if necessary.

The blocking means associated with each passing means ts, however, preferably situated outside {adjacent or at a distance thereof) the guiding surfaces, during operation together with the guiding surfaces in a substantially vertical plane. In that cane the blocking means can be arranged in such a way that it is positioned in line with the guiding surfaces during operation of the tensioning device.The blocking means can be arranged such that it is contiguous to the upper end of the guiding surfaces during operation of the tensioning device. Zt is also possible that the blocking means is contiguous to the lower end of the guiding surfaces or that a blocking means is provided on the upper end as well as the lower end of the guiding surfaces.

The tensioning device can in addition be adapted for use with an anchor line at least partly consisting of a chain, in that the guiding surfaces consist of gliding surfaces for guiding first chain links and a slot arranged between the gliding surfaces for guiding having during use their main axis which is perpendicular to their main plane positioned in a substantially horizontal plane and a slot located between the gliding planes for guiding the intervening, second chain links lying in a substantially vertical plane during use, the guiding surfaces ending in the blocking means comprising two protruding blocking cams for blocking one of the first links.

The tensioning device can be realized such that the normal of each passing means interseets the central axis in the facing portions, so that those facing portions are arranged in a vertical plane with the central axis.

According to a preferred embodiment, the tensioning device may comprise a plurality of detachable, joinable tensioning elements, each comprising a passing means with associated blocking means. These tensioning elements can be joined at the place of the central axis in a star-shaped arrangement.

The tensioning elements can be realized and mounted such that the passing means can pivot in a vertical plane with regard to the remaining part of the tensioning device.

According to another preferred embodiment, the tensioning device is formed as a crown wherein end portion which in use of the tensioning device is situated on top io provided with a connecting means for a hoisting line at the central axis, in that the passing means are arranged on the inside of a ring-shaped part, extending about the central axis, said ring-shaped part being located at a distance along the central axis below the end.portion and being connected the end portion by means of posts, the posts limiting in tangential direction of the crown-shaped tensioning device passing spaces, positioned together in a same vertical plane and providing a passage for the anchor line. from inside the tensioning device to outside.

The star-shaped and crown-shaped preferred embodiments are especially suited for applicatibn in a single point mooring system, wherein after having made the anchors suffieiently penetrate, a buoy is connected to a hoisting line to then tension the single point mooring system.

The passing means can also be arranged with their avgociated blocking means on a frame around the central axis. This frame can be a polygon, preferably regular, having arranged on its vertices one or more passing means with associated blocking means. As will appear from the following, such a tensioning device is especially advantageous for use during installation of a TLP.

The invention also relates to tensioning a plurality of opposing anchor lines and thereby making a plurality of anchors connected to the first ends of anchor lines penetrate into the mooring bed, using the tensioning device according to the invention, comprising the following Steps: a) passing of the anchor lines to be tensioned through the passing means of the tensioning device meant for that purpose and described above, the anchor lines at their second end being extended by means of pendant lines; b) putting out the anchors to the respective positions situated dividedly around the location to be reached of the tensioning device; c) lowering the tensioning device by the hoisting line(s) as far as possible; d) drawing tighter the pendant lines of a first number of anchor lines, the anchors connected therewith being positioned with reward to eachother each time on both sides of a respective plane enclosing the central axis of the tensioning device in lowered position, the anchor lines being brought into engagement with their associated passing means; e) bringing the tensioned anchor lines into engagement with the added blocking means; f) pulling up the tensioning device by pulling the hoisting lines) connected to the tensioning device, with the result that the anchors connected to the first number of anchor lines are pulled towards eachother and will penetrate in the mooring bed; g) letting the hoisting line(s) render to drop the tensioning device as far as possible, h) bringing out of engagement with the blocking means the first number of anchor lines and drawing tighter the pendant lines thereof; i) repeating several times the steps e)-g) till the respective anchors have penetrated in order to provide sufficient grip; j) bringing out of engagement with the blocking means of the tensioned anchor lines; k) arranging over the correct poSition the tensioning device by alternately drawing tight the pendant lines; and 1) drawing tight handled anchor lines and bringing them into engagement with the associated blocking means.

If the total number of anchor lines to be tensioned makes it necessary, with respect to the desired pulling forces, to tension a plurality of sets of anchor lines in a successive manner, steps d)-j) are repeated for next sets of anchor lines.

A buoyant body can be attached to the hoisting line or hoisting lines of the invention, by means of which the tensioning device can be pulled up again after having the anchors make penetrate the scoring bed to p the anchor lines tensioned. The buoyant body may consist of a buoy connected by means of one hoisting line to the tensioning device and which is brought into the desired buoyancy after displacement along the hoisting line towards the tensioning device.

The buoyant body can also be formed by a TLP (Tension Leg Platform) which can also serve as a vessel from which the tensioning device ii operated during tensioning the anchor lines and resulting penetration of the anchors. In that case, the tensioning device is in that case preferably realized as a frame, for providing a passage to pipe systems etc., which extend between the TLP and the mooring bed. After the anchors have sufficiently penetrated, the tensioning frame is connected to the lower extremities of the tension legs of the TLP, whereafter the tension legs are tensioned so that the tension frame is pulled up in order to tension the anchor lines therewith.As was the case with the SPM, here the anchored tensioning device will stay in its position in a horizontal sense.

Should the tensioning forces to be exerted by the TLP tension legs or the hoisting line connected to the buoy of a SPM be so large that the tensioning device would provide a too small opposing vertical force or that the tensioning device after tensioning of the tension legs or hoisting line would become situated at such a distance of the mooring bed that as a result of the more vertical extension of the anchor lines towards the anchors the holding force provided by these anchors would decrease too much, than it can be considered to attach a ballasting frame or block by means of one or more pulling lines at a distance underneath the tensioning device prior to lowering both down to the mooring bed, and to subseguently execute step f till the ballasting frame or block comes up as well, and that tensioning of the tension legs or lines takes place while the the ballasting frame or block is kept on the mooring bed.

During tensioning of the tension legs the vertical reaction force required is provided by the anchor lines at the place of the blocking means, and, via the pulling lines, by the ballasting frame.

The invention will now be described more detailed by means of some embodiments only given as an example, with reference to the enclosed drawings, wherein; Fig. 1A is a top view of an embodiment of the tensioning device according to the invention; Fig. 1B is a cross-section along line IB-IB in Fig. IA; Fig. 2A is a top view of a second embodiment according to the invention, wherein, however, some parts arc left out; Fig. 2B is a cross-section along the line tSB-tTB of Fig. 2A; Fig. 3A is a vertical cross-section through a part of a third embodiment of the tensioning device according to the invention, without blocking action;; Fig. 3B is a eross-section similar to Fig. 3A, but in this case with blocking action; tig. 3C is a top view on the arrangement of Fig. 3A; Fig. 4A shows a fourth embodiment of the tensioning device according to the invention in horizontal cross-section; Fig. B is a cross-section along line IVB-IVB of Fig 3; Figs. 5A, B, C, show schematically three embodiments of frame shaped tensioning devices according to the invention, with anchor lines; Fig. 6 shows a possible arrangement at a vertix of a frameshaped tensioning device according to the invention; Fig. 6A shows a cross-section of one of the tensioning elements of Fig. 6;; Fig. 69 shows a top view of the tensioning element of Fig. 6A; Fig. 7 shows a frame-shaped tensioning device with a ballasting frame in position after tensioning and positioning a TLP; Fig. 7A shows a detail of a vertix of the tensioning device of Fig. 7; and Pig. 8 is a schematic view of a single point mooring system comprising a tensioning device according to the invention In Fig. 1A, a first star-shaped embodiment of a tensioning device according to the invention is indicated at 1, being composed of six tensioning elements 2, each determining a passage 3 for an anchor line (not shown). The passages 3 are limited outwardly by guiding surfaces 6, being substantially turned towards the centre of the tensioning device.The guiding surfaces 6 comprise gliding surfaces 8 and an int.rmediate slot 9. ln Figs. tA and 1B it can be oeen that each tensioning elem*nt.is provided with a clamp 11, of which both legs are provided with an aperture 5S.The tensioning elements 2 are joined together by passage of a pin 10 through the respective apertures 55, a stop ring 13 ensuring that the tensioning elements are kept in their place with regard to the pin 10. At its upper end the pin is provided with an attaching eye 5 for a hoisting line, and at its lower end with an attaching eye 14 for a ballast block, if necessary. In the tensioning element depicted on the left in Fig. lB, an anchor chain 17 is passed through and this chain extends upwardly in the direction A and towards one or more anchors (not shown) in the direction B.The first links 20, the third main axis thereof extending in the plane of the drawing, find guidance by slot 9, whereas the second links 21, extending in the plane of the drawing, find guidance on gliding surfaces 8. As visible, the guiding surfaces run inwardly from the bottom side of the tensioning element and subsequently bend upwardly in order to contact a vertical plane and to be continued upwardly and outwardly. In the embodiment of the tensioning device shown in figs. lA and lH the facing portions 7 of the guiding surfaces are faced straight towards the central axis 4-4. It is noted that the tensioning elements 2 can be joined to form the tensioning device 1 in such a way, that rotation of one tensioning element 2 with regard to the other tensioning elements and the pin 10 is possible. As a result a certain degree of self alignment of the tensioning elements with respect to the anchor lines during tensioning can take place. This provision is also possible with other embodiments of the tensioning device.

The gliding surf aces end at their upper end tn cams 15, by which one of the first links 2b can be brought in blocking engagement.

Zn the tensioning element 2 depicted on the left in fig. lB, the chain is nct in engagement with the blocking cams 15 and the chain 17 can be passed through the tensioning device 1 in both directions.

On the right in Fig. 1B the situation is shown in which the chain 18 with. one of its first links 20 is brought into engagement with the blocking cams 15, so that the chain 18 cannot pass downwardly through the tension device 1. In order to achieve this situation part 19 of the chain, which extends upward from the tensioning device, is turned outwardly and downwardly around the left tensioning element 2. Not shown is that the upper end of chain 18, as well as chain 17, is connected to a pendant line, by means of which the upper end of these chains can be pulled up or lowered as desired.The pendant line could possibly be woved in horizontal direction from the central axis, to thereby put part 19 outwardly around the tensioning element. Zn order to outwardly and downwardly turn the chain around the tensioning device, a turn over means could be provided at the upper end of the tensioning device, which turn over means upon slackening of the respective pendant line forces part 19 outward, so that upon paying out said pendant line part 19 falls outwardly around the tensioning element. The turn over means could, for example, be formed by a ratchet 54, which by its own weight forces part 19 of the chain outward when the tension in part 19 has been sufficiently decreased.

The tensioning elements can also be mounted in such a way, that they are turnable in the vertical plane in order to bring the blocking means into or out of engagement with the anchor lines. Zn Figs. 2A and 2B such a tensioning device is shown, comprising two tensioning elements 12, which number, however, could be large. By means of pivoting pins 56 the tensioning elements 12 are pivotally attached to radial plates 58 of pin 10. Visible are again the gliding surfaces 8 and the slot 9, whereas furthermore guiding surfaces 59 are provided for guiding chain 17 on the radial inside of the passage 3.In the position of the tensioning elements shown in Fig 2B, the first links 20 are in blocking engagement with the blocking cams 15 positioned at the lower end of the gliding surfaces. When pulling forces are exerted on the chain 17, in the direction of C, the next first links can pass around the cams 15, upwardly with respect to the tensioning device. Zn order to bring and keep the chain and the blocking cams out of blocking engagement with each other it is advantageous to provide for example for an attaching eye 57 for attachment of a pulling line, by means of which tensioning element 12 can be pivoted around pivoting pin 56.

In Figs. 3A-C a tensioning device 72 is shown, which is pivotally mounted with its side plates 73 on a central part 70 formed by a pin or frame by means of a pivoting pin 69. A U-shaped attachment member 71 protrudes from the central part 70, accomodating the pivoting pin 69 and forming an inner limit for the passage 3 of the chain 18. In rig. 3A the situation is shown in which the tensioning device 72 under its own weight is pivoted around a pivoting pin 69 till an abutment 74. The tensioning element 72 can now be brought upward along chain 18 without the first links 20 thereof coming into blocking engagement with the blocking cms 15 here contiguous to the upper end of gliding surfaces 8. In this situation other, not shown anchor lines can be tensioned.In Pig. 3c the passage 3 is shown in the situation of Fig. 3A. When the chain 18 is to be tensioned by means of the tensioning device, the chain IS is tigtened first by the exertion of a pulling force in the direction D. The part of chain is between tensioning device and anchor will then exert a force K passing underneath the pivot 69 and hence a counter clockwise turning moment on the tensioning element, so that the cams 15 move into the path of the chain, possibly Oven become positioned against the U-shaped attachment portion 71. If necessary the tensioning device is then somewhat raised till the cams 15 engage in a blocking way with the bottom side of a first link 20.

subsequently, the chain 18 can be lowered with part 19 over the tensioning element by means of the pendant line 74 and the actual tensioning of the chain 18 can be continued by raising the tensioning device. After a certain maximal tension in the hoisting line(s) has been reached, the tensioning device is lowered a little again to decrease the tension in chain 18. The tensioning element will then tend to pivot back and by subsequently pulling up the pendant line 74 part 19 can be brought in a vertical position again so that the tensioning element can pivot further towards the position indicated in rig. 3A and the tensioning device can be lowered along chain 18 to start z new cycle.

In the Pigs. 4A and 4B another embodiment of the tensioning device' according to the invention is shown, wherein corresponding reference numerals are.used again for corresponding parts. The tensioning device shown in Figs. 4A and 4B is crown-shaped and constituted by an upper situated ring-shaped portion 27 and a lower situated, substantially ring-shaped portion 29, the two ring-shaped portions being connected by poets 28 extending substantially in vertical direction. Both ring-shaped portions 27 and 29 and the posts 28 determine passages 30 for anchor chains 17 and 18. The central axis 4-4 forms in this case the axis of symmetry of the crownshaped tensioning device.In the centre the upper positioned ringshaped portion 27 is provided with a spherical trunnion bearing cup 24 for bearing a ball trunnion body 23, a ball trunnion rod 25 upwardly extending through a central aperture 26 in the scale 24 being integrally formed therewith. The pivot rod 25 is at its upper end connected to a hoisting line. As the tensioning device of Figs.

1 and 2, the crown-shaped tensioning device is composed of six passing parts 22, which form part of the lower situated, substantially ringshaped portion 29. It is emphasized that the number of passing portions can be each number larger than 1.

The passing portions 22 comprise again guiding surfaces 6, being composed of gliding surfaces 8 for first links 20 and a slot 9 for second links 21. Here, the guiding surfaces 6 extend from the bottom side of the tensioning device inward and upward in a vertical plane comprising the central axis (4-4) and continue via a vertical portion 7 upward and outward. This time the blocking cams 15 are situated at the lower end of the gliding surfaces 8. On the left in Fig. 4B chain 17 is shown again in a situation wherein it can move freely through the tensioning device. On the right in Fig. 4B the situation is shown once more wherein the upper portion 19 of chain 18 is turned around the passing portion 22, so that one of the first links 20 is in an engaging position with the blocking cams 15 so that chain 18 cannot move downward with respect to the tensioning device.

Furthermore, an other pair blocking means 31 can be seen, spaced at a distance from the blocking cams 15, which distance, measured along the gliding surfaces 8, is unegual to the centre-to-centre distance of the first links. As a result the length of stroke between the succeeding blocking situations for the chain is shortened.

In Figs. 5A-C some frame-shaped tensioning devices are diagrammetically shown, which frames form z square 32, a rectangular 33 and a regular pentagon, resE ctlvely. At the vertices of the frames 32, 33 and 34 several tensioning devices are provided, as for example shown in Fig. 6 in the tensioning elements 37A-P, which are in that case situated on the vertix 35 of the frame members 36. It is noted that Fig. 6 is a diagrammatic representation.

Prom the vertices of the frame 32, 33, and 34 shown in Figs.

5A-C, schematically drawn, anchor lines run to anchors connected therewith. The tensioning of the different anchor lines and so making the therewith connected anchors penetrate into the mooring bed will be discussed later under reference to the a'rrangment shown in Fig.

5B.

Returning to Fig. 6, in which the vertix 35 of a frame-shaped tensioning device is shown, the chain-shaped anchor lines 38A-E are inserted through the associated tensioning elements, respectively.

The situation shown, wherein the first links of the chains 38A-S are brought into blocking engagement with the tensioning devices 37A-E, respectively, is in the present case, wherein a laroe number of anchor lines are to be tenlionedr applicable when the bringing to the desired holding force of all anchors by use of the tensioning device is completed. This situation occurs after step L of the formerly described method according to the invention. Also shown are the pendant lines 39A-E connected to the ends of chains 38A E opposed to the anchors. By tightening the pendant lines 39A-E the chains 3SA-E can be brought out of blocking engagement with the tensioning elements 37A-E.

Zn Fig. 6A and 6B a tensioning element 37A is shown which is suitable to be attached onto the vertix 35 by means of an attachment plate 51. By means of two side plates 52, the guiding surfaces 8 and 9 are connected to the plate 51, a passage 3 being determined therebetween.

In Fig. 7 an end situation is shown of a positioned TLP, anchored by means of anchors. A semi-submerriblr 40 can be seen at the water surface 49. A pipe stand 41 extends downward through the semi- submersible towards a oChristmas-tree, system" 42 at the mooring bed 45. Straight underneath the emi-submersible 40 there is a ballasting frame 46 on the mooring bed. By means of pulling lines 47, this ballasting frame 46 is connected to a tensioning frame 35, situated thereabove, which in its turn is connected to the bottom side of the semi-submersible 40 by means of a plurality of hoisting lines 48.At the vertices of the tensioning frame 33 there is a plurality of tensioning elements, the blocking means thereof being in blocking engagement with the first links of anchor chains leading towards anchors, such as anchor chain 38A leading to the anchor 43 penetrated in the mooring bed 45. The other end of the anchor chain passes over tensioning element 37A downward and subseqiiently changes over into the lower end of a pendant line 39A, which leads to a haul and paying out device provided on the sem--submerstble 40. Furthermore, the sling line 44 for the anchor 43 is shown.

In Pig. 7A a detail of the vertix 35 of the tensioning frame 33 of the arrangement of Pig. 7 is shown. Visible therein is that the upper end of the pulling line 47 is connected to the lower side of the tensioning frame 33, whereas the tensioning frame 33 is connected with its upper side to the lower end of the hoisting line 48. Also visible in Figs. 7 and 7A are tension legs 50 of the TLP, which extend from the semi-submersible 40 towards the tensioning frame 33.

In tensioning the anchor lines by means of the tensioning device according to the invention and thereby having the anchors penetrate the mooring bed in order to obtain the situation as shown in Fig.

7, the procedure could be as follows: The tensioning frame 33 together with the ballasting frame 46 situated therebelow and connected therewith, is lowered from the semi-submersibie 4 by the hoisting lines 48. Prior to this the necessary anchor line. have been already passed through the tensioning elements of the tensioning frame. When the ballasting frame 46 has been lowered to the correct location on the mooring bed 45r the anchors pre distributed and lowered on their sling lines onto.the scoring bed 45 around the anchoring location of the TLP by means of an auxiliary vessel. Care should be taken that the anchor lines are not pulled so far through the tensioning frame 33 that the anchor lines concerned cannot be brought into engagement anymore with the blocking means involved.Then, the anchor lines which are to be tensioned first are pulled, whereafter by manipulation of their pendant lines it can be effected that the connected end portions of the anchor lines concerned drop outward and downward so that their first links 20 are brought in blocking engagement with the blocking means of the tensioning elements concerned.

Reference is now being made to Fig. SB. Here, the tensioning frame 33 has four vertices a, b, c, d, on each of which in this schematic case three tensioning elements are arranged, so that seen clockwise twelve anchor lines are visible, al, a2, a3, bl, b2, b3, cl, c2, c3, dl, d2 and d3, respectively. The tensioning can now be carried out such that first the anchor lines al and b3 are tensioned against each other. ln this tensioning frame the vertical portions of the guiding surfaces of the respective tensioning elements face each other straight, i.e. their normals are aligned. By manipulation of the hoisting lines 48, which are for example connected to the vertices, the tensioning frame can be kept straight. After the tensioning frame 33 has been lifted for a first time to such an extent that the pulling lines 47 are tensioned and the ballasting frame 46 threatens to come off the mooring bed 43, the tensioning frame 33 is lowered again to the ballasting frame 46 and the anchor lines al and b3 are again pulled tight by hauling in their pendant lines.

Then, by manipulation of the pendant lines, the anchor lines al and b3 are brought into engagement with the blocking means of the respective tensioning elements again and the tensioning frame is pulled up again by the hoisting lines, whereafter the preceding procedure is repeated several times till the forces required for pulling the tensioning frame up have become so large, that can be assumed that the anchors have sufficiently penetrated. Next, with the tensioning frame 33 down at the ballasting frame 46 again, it is ensured by means of manipulation of the pendant lines that the anchor lines al and b3 are brought out of engagement with the blocking means of the respective tensioning eements and the anchor lines will become slack.Then, the anchor lines cl and d3 can be dealt with, or the lines a3 and dl or, for example, the lines a2, b2, c2 and d2. It will be obvious that many different sequences of tensioning are possible, and alro that the number of anchor lines that can be tensioned against each other can be varied. It is important that following sets of anchor lines can be tensioned against each other, without this tensioning being influenced by already tensioned anchor lines. Thus, all sets of anchor lines which have to be tensioned against each other can be tensioned by a same force.

After all anchors have been tensioned, the tensioning frame is centered above the ballasting frame by pulling in the anchor lines as much as necessary by their pendant lines and by bringing them into engagement with the blocking means of the respective tensioning elements. Subsequentlg, the tension legs 50 are lowered from the setni-submersible 40 and brought in connecting engagement with the tensioning device 33 at means 53 (Figs. 7, 7A). Next, the tension legs 50 are tensioned from the semi-submersible 40, by increasing the buoyancy of the semi-submersible 40.During this tensioning the frame 33 will be pulled up till a vertical balance of force is reached, wherein the upward oriented force exerted by the tension legs 50 on the frame 33 is in balance with the vertical forces transferred to the tensioning frame 33 by the anchor lines at the tensfoning elements and by the downward oriented forces exerted on the tensioning frame 33 by the pulling lines 47. Because of the anchors distributed about the tensioning frame 33 and tensioned by the anchor lines the tensioning frame is kept in position in horizontal sense.

Zt is noted that for anchoring a TLP it need not always be necessary to include a ballasting frame into the anchoring arrangement. In that case, as with a Single Point Mooring system (SPM) wherein the tensioning device is connected with one hoisting line to a buoy situated near the water surface, during tensioning of the anchor lines the tensioning device is lifted each time till there occurS a situation in which the pulling force exerted on the anchors has z vertical component which is too large, or till the pulling capacity of the tensioning device for the hoisting lines is approached.

In Fig. 8 the final situation is shown in case the tensioning device is used in a 1PM. Here, the tensioning device 60 can be reali2ed as the tensioning devices shown in Figs. lA,B, 2A,B or 3A, 3B, 3C, 4A 4B. A buoy 63 ensures that line 62 and lines 68A P are tensioned. Horizontally viewed, lines 68A-F run star-like from the tensioning device and are at their one end connected to anchors 67A-F penetrated in the mooring bed 66. Line 62 is passed through buoy 63 to the water surface 65 and is held within reach for mooring a ship by means of floats 64. The buoy may have an adjustable buoyancy, so that the buoy 63 after penetration of the anchors 67A-F can be lowered along line 62 underneath the water surface 65, in order to subsequently raise the buoyancy strongly with the result that the lines obtain the desired tension.

It is noted that where in the description vertical or horizontal extension, orientation etc. of certain portions or of the tensioning device is mentioned, the ideal situation during use is referred to, wherein, of course, limited deviations of that situation by an inclined position of the tensioning device are included.

Claims (1)

1. Tensioning device for passing through and tensioning at least one anchor line and thereby making that one or more anchors connected to one end of the anchor line penetrate a mooring bed, comprising at least one passing means for passing the anchor line through the tensioning device, the passing means comprising guiding surfaces for guiding the anchor line, in a substantially vertical plane during use, and at least a blocking means associated with the passing means, for preventing relative movement of the tensioning device along the anchor line in a direction away from the anchor, cHMtACflZZZD in that the tensioning device comprises a central axis (4-4) being substantially vertically oriented during use of the tensioning device, and in that the tensioning device furthermore comprises a plurality of passing means for a corresponding number of anchor.lines the passing means being distributed about the central 'axis, the guiding surfaces of each passing means comprising facing portions substantially facing towards corresponding parts of guiding surfaces of one or more other passing means, as well as connecting means for connection of the tensioning device to at least one hoisting line to exert a vertical force on the tensioning device during use.

2. Tensioning devisee according to claim 1, CHARACTERIZED in that the blocking means associated with each passing means is arranged such that, if necessary, this blocking means and the respective anchor line can be brought into a blocking engagement with eachother, but otherwise allow free passage of the anchor line across the guiding surfaces in two opposite directions.

3. Tensioning device according to claim 2, cEaRAc5ER5zrn in that the blocking means associated with each passing means is positioned outside the guiding surfaces and in use is positioned together with the guiding surfaces in a substantially vertical plane.

4. Tensioning device according to claim 3, CHARACTERIZED in that the blocking moans associated with each passing means is arranged such that it is aligned with the respective guiding surfaces

5. Tensioning device according to claim 4, CwA=R=D in that the blocking means is arranged such that in the situation of use, it is contiguous to the upper end of the guiding surfaces 6.Tensioning device according to claim 3, 4, or 5, CHARACTERIZED in that the tensioning device is adapted for use with an anchor line at least partly consisting of a chain in that the guiding surfaces consist of gliding surfaces for guiding first chain links having during use their third main axis which is perpendicular to their main plane positioned in a substantially horizontal plane and a slot located between the gliding planes, for guiding the intarvening, second chain links lying in a substantially vertical plane during use, the guiding surfaces ending in the blocking means which comprises two protruding blocking cams for blocking one of the first links.

Tensioning device according to any one of the claims 1-6, CHARACTERIZED in that the normal on the facing portions of the guiding means of each passing means intersects the central axis

8. Tensioning device according to any one of the claims 1-7, caRA2fRt:ED in that the tensioning device comprises a plurality of detachable, joinablO tensioning elements (2; 12; 37a-e), each comprising a passing means with associated blocking means;

9. Tensioning device according to claim 7, CHARACTERIZED in that the tensioning elements are assembled in a starshaped arrangement at the central axis 10.Tensioning device according to claim 8 or 9, CEARAC$E2zZED in that the tensioning elements are mounted pivotally onto a central part of the tensioning device, for pivoting in a substantially vertical plane.

11. Tensioning device according to any one of the claims 1-8, CHARACTERIZED in that the tensioning device is formed as a crown, wherein an end portion which in use of the tensioning device is positioned on top is provided with a connecting means for a hoisting line at the central axis in that the passing means are arranged on the inside of a ring-shaped portion extending about the central axis, said rtng-sheped portion being located at a distance along the central axis below the end portion and being connected to the end portion by means of posts the posts limiting in tangential direction of the crown-shaped tensioning device passing spaces positioned together in & same vertical plane and providing a passage for the anchor lines from inside the tensioning device to the outside.

12. Tensioning device according to any one of the claims 1-8, CHARA=ZRIZZn in that the passing means with their associated blocking means are arranged on a frame extending about the central axis.

13. Tensioning device according to claim 12, CHARACTERIZED in that the frame is a polygon having one or more passing means with associated blocking means on the vertices

14. Tensioning device according to claim 13, CHARACTERIZED in that the frame is a regular polygon.

15. Tensioning device according to any one of the preceding .claims, CHARACTERIZED by connecting'means for connection to a ballasting means.

16. Tensioning device according to any one of the preceding claims, CHARACTERIZED in that the guiding surfaces have a curving course, the facing portions being positioned in the outer curve thereof.

17. Method for tensioning a plurality of opposing anchor lines and thereby making a plurality of anchors connected with first extremities of the anchor lines penetrate a mooring bed, CzARa=RZZZD by a) passing the anchor lines to be tensioned through the passing means destined therefore of the tensioning device according to any one of the preceding claims, the anchor lines being extended at their second end by means of pendant lines; b) paying out the anchors to respective positions distributed about the desired location of to tensioning device; c) lowering the tensioning device by the hoisting Lines as far as possible; d) pulling the pendant lines of a first plurality of anchor lines, the anchors connected -therewith each time being positioned with regard to eachother on either side of a respective plane comprising the central axis of the tensioning device in lowered condition, the anchor lines being brought into engagement with their respective passing means; e) bringing the tension anchor lines into engagement with the associated blocking means; f) lifting the tensioning device by pulling the hoisting lines connected to the tension4ng device, whereby the anchors connected to said first plurality of anchor lines are pulled towards eachothcr and will penetrate in the mooring bed; g) paying et the hoisting line(s) to lower the tensioning device as far as possible, h) bringing out of engagement with the blocking means said first number of anchor lines and pulling the pendant lines thereof; i) repeating several times the steps e)-g) till the respective anchors have penetrated for providing sufficient holding force; j) bringing out of engagement with the blocking means the tensioned anchor lines; k) positioning the tensioning device above the correet location by alternately pulling the pendant lines; and 1) tightening handled anchor lines and bringing them into engagement with the associated blocking means.

18. Method according to claim 17, ttAtACTERIZED by repeating the steps d)-j) after step j) for one or more following pluralities of anchor lines.

19. Method according to claim 17 or 18, CHARACTERIZED by attaching a buoyant body to the hoisting line or hoisting lines and displacing the buoyant body along that line towards the tensioning device in order to have the tensioning device Fulled up by the buoyant force and to tension the anchor lines therewith.

20. Method according to claim 19, aLMAC-LISID in that the buoyant body consists of a buoy connected with the tensioning device by means of z hoisting line forming a tension connection, and being brought to the desired buoyancy after displacement along the hoisting line.

21. Method according to claim 19, CHARACTERIZED in that the tensioning device is realized as a frame and is connected by means of several hoisting lines with a TLP as buoyant body, wherein after making the anchors sufficiently penetrate the mooring bed, the tensioning device is connected with the lower ends of the TLP tension legs of the TLP forming a tension connection and wherein the tensioning device is 'pulled upward by tensioning the tenSiOn legs in order to tension the anchor lines.

22. Method according to claim 20 or 21, CHARACTERIZED in that prior to execution of step c) a ballasting means is attached at a distance underneath the tensioning device by means of one or more pulling lines, in that during step c) the ballasting means is lowered to the mooring bed, in that step f) is executed till the ballasting means comes up as well, and in that tensioning of the tension connection takes place while the ballasting means is kept on the mooring bed.

23. Assembly CHARACTERIZED by a TLP , and a tensioning device according to any one of the claims 1-16, the tensioning device being attached to the lower end of the tension legs of the TLP and being connected to anchors penetrated into a mooring bed by means of a plurality of anchor lines , extending about and from the tensioning device.

24. Assembly CHARACTERIZED by a buoy and a tensioning device according to any one of the claims 1-16, the tensioning device being attached to the lower end of a mooring line substantially extending in a vertical direction, and being tensioned by the buoy which is attached to the mooring line at x higher situated location, wherein the tensioning device is connected to anchors penetrated into. a mooring bed by means of a plurality of anchor lines extending about and from the tensioning device 25. Assembly according to claim 23 or 24, CHARACTERIZED by a ballasting means which is connected to the tensioning device positioned thereabove by means of pulling lines and is situated on the mooring bed

26. Tensioning device for passing through and tensioning at least one anchor line substantially as hereinbefore described with reference to the accompanying drawings.

27. A method for tensioning a plurality of opposing anchor lines substantially as hereinbefore described with reference to the accompanying drawings.

28. An assembly substantially as hereinbefore described with reference to the accompanying drawings.