GB1585123A - Structures having buoyant chambers - Google Patents
Structures having buoyant chambers Download PDFInfo
- Publication number
- GB1585123A GB1585123A GB827276A GB827276A GB1585123A GB 1585123 A GB1585123 A GB 1585123A GB 827276 A GB827276 A GB 827276A GB 827276 A GB827276 A GB 827276A GB 1585123 A GB1585123 A GB 1585123A
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- GB
- United Kingdom
- Prior art keywords
- tether
- gripper means
- gripper
- moving
- tension
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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- 238000000034 method Methods 0.000 claims description 16
- 230000003247 decreasing effect Effects 0.000 claims description 7
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 4
- 238000010276 construction Methods 0.000 description 2
- 238000006073 displacement reaction Methods 0.000 description 1
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 description 1
- 239000010931 gold Substances 0.000 description 1
- 229910052737 gold Inorganic materials 0.000 description 1
- 238000003780 insertion Methods 0.000 description 1
- 230000037431 insertion Effects 0.000 description 1
- 238000012423 maintenance Methods 0.000 description 1
Classifications
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B7/00—Special methods or apparatus for drilling
- E21B7/12—Underwater drilling
- E21B7/128—Underwater drilling from floating support with independent underwater anchored guide base
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
- B63B—SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING
- B63B21/00—Tying-up; Shifting, towing, or pushing equipment; Anchoring
- B63B21/50—Anchoring arrangements or methods for special vessels, e.g. for floating drilling platforms or dredgers
- B63B21/502—Anchoring arrangements or methods for special vessels, e.g. for floating drilling platforms or dredgers by means of tension legs
Landscapes
- Engineering & Computer Science (AREA)
- Geology (AREA)
- Life Sciences & Earth Sciences (AREA)
- Mining & Mineral Resources (AREA)
- Environmental & Geological Engineering (AREA)
- Fluid Mechanics (AREA)
- Physics & Mathematics (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Geochemistry & Mineralogy (AREA)
- Chemical & Material Sciences (AREA)
- Combustion & Propulsion (AREA)
- Mechanical Engineering (AREA)
- Ocean & Marine Engineering (AREA)
- Other Liquid Machine Or Engine Such As Wave Power Use (AREA)
Description
(54) IMPROVEMENTS IN AND RELATING TO STRUCTURES
HAVING BUOYANT CHAMBERS
(71) We, EXTON & GOLD LIMITED, a British Company, of Gate House, The
High, Harlow, Essex, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following method:
The invention relates to structures having buoyant chambers and more especially to structures suitable for use offshore and to structures of the kind generally referred to as tension leg structures.
Tension leg structures generally consist of a buoyant chamber that is anchored by " tethers " such as cables or ropes under tension to the sea bed so that the buoyant chamber is located below the surface of the water. On the buoyant chamber is mounted a platform which is located above the surface of the water. The tethers, which are usually cables or ropes, must generally be maintained under very high tensions and during construction and often during maintenance of the structure it is necessary to tighten up and/or slacken off the tethers.
The necessary tension in each tether is usually at least 300 tons weight requiring large diameter cables or ropes and very large winches would be required for such a purpose. Space on a tension leg structure is, however, very limited and there are also difficulties in the construction and use of a winch of suitable dimensions.
The invention provides a structure which comprises a tethered portion comprising a buoyant chamber and a platform supported on the buoyant chamber, the structure also comprising anchor means, a plurality of tethers extending from the tethered portion to the anchor means, and means for varying the tension of at least one of the tethers comprising first and second gripper means for gripping the tether, each of the gripper means being arranged to allow relative movement between the gripper means and the tether such that the tether can move relative to the gripper means in a forward direction in which, in use, tension in the tether is increased but be capable of gripping the tether to prevent relative movement of the tether in the reverse direction, and means for moving the first gripper means reciprocally relative to the tethered portion in the forward and reverse directions, the arrangement being such that in operation, when the first gripper means is moving in the forward direction it can grip the tether so that there is relative movement between the tether and the second gripper means and when the first gripper means is moving in the reverse direction the second gripper means can grip the tether so that there is relative movement between the tether and the first gripper means.
The invention also provides a method of increasing tension of a tether extending from a tethered portion, comprising a buoyant chamber and a platform supported on it, to anchor means, of a structure, which method comprises engaging the tether in first and second gripper means, each of the gripper means being arranged to allow relative movement between the gripper means and the tether such that the tether can move relative to the gripper means in a forward direction in which tension in the tether is increased but be capable of gripping the tether to prevent relative movement of the tether in the reverse direction, moving the first gripper means reciprocally relative to the tethered portion in the forward and reverse directions so that when first gripper means is moving in the forward direction it grips the tether and there is relative movement between the tether and the second gripper means and when the first gripper means is moving in the reverse direction the second gripper means grips the tether and there is relative movement between the tether and the first gripper means.
When the first gripper means is moving in the forward direction it can grip the tether and urge it in the forward direction increasing the tension of the tether, which is secured to- the anchor means. When the first gripper means is moving in the reverse direction, the second gripper means can grip the tether and retain the increased tension of the tether caused by the forward movement of the first gripper means. This operation can be repeated as many times as necessary to increase the tension progressively until the desired tension of the tether is reached.
With the apparatus and method of the invention the tension of the tether can be increased to 600 to 800 tons weight and even as high as 21000 tons weight, the apparatus of the invention needing only a relatively small space on the tethered portion. The tether may be a cable or rope of 5" or 6" in diameter or up to 9" in diameter or higher depending on the tension required.
The second gripper means may be fixed relative to the tethered portion. Alternatively, the means for varying the tension may also comprise means for moving the second gripper means reciprocally relative to the tethered portion in the forward and reverse directions, the arrangement being such that when the first gripper means is moving in the forward direction the second gripper means is moving in the reverse direction and when the first gripper means is moving in the reverse direction the second gripper means is moving in the forward direction. With this arrangement, when the first gripper means is moving in the reverse direction, the second gripper means grips the tether and urges it in the forward direction further increasing the tension in the tether.
Thus, the tension in the tether can be increased continuously rather than intermittently.
Advantageously, the first gripper means is located vertically above the second gripper means.
Each of the first and second gripper means is advantageously such that it tends to grip the tether more firmly the greater the force on the tether urging it to move in the reverse direction. Suitable gripper means are those sold under the name of "Lucker".
The means for reciprocally moving the first gripper means relative to the tethered portion, and the means for reciprocally moving the second gripper means, when provided, advantageously comprises hydraulic means, and preferably one or more hydraulic rams. The means for reciprocally moving the or each gripper means may be operable manually to reverse the direction of movement each time the or each gripper means reaches the limits of its stroke. Alternatively, the means may be operable to reverse the direction of movement automatically, and to achieve this, trip switches may be located at the limits of the stroke and be operable by the gripper means itself when it reaches the said limits.
To give an indication of the tension in the tether a gauge may be provided in the hydraulic circuit, or, alternatively, load cells or strain gauges may be located elsewhere in the apparatus, for example, on the tether itself.
Advantageously, the first and second gripper means are so arranged that they can be released to allow the tether to move in the reverse direction relative to the gripper means.
Accordingly, the invention also provides a method of decreasing tension of a tether extending from a tethered portion, comprising a buoyant chamber and a platform supported on it, to anchor means, of a structure, which method comprises engaging the tether in first and second gripper means, each of the gripper means being arranged to allow relative movement between the gripper means and the tether such that the tether can move relative to the gripper means in the forward direction in which tension in the tether is increased but be capable of gripping the tether to prevent relative movement of the tether in the reverse direction, each of the gripper means also being so arranged that it can be released to allow the tether to move in the reverse direction relative to the gripper means, and the tension in the tether is decreased by releasing the second gripper means and moving the first gripper means, which grips the tether, in the reverse direction, causing the second gripper means to grip the tether, releasing the first gripper means and moving the first gripper means in the forward direction relative to the tether. The tension in the tether can also be decreased continuously, rather than intermittently, as when increasing the tension.
Means for varying the tension of the tether comprising first and second gripper means may be provided for each tether of the structure, but, advantageously, a plurality of second gripper means is provided, each for a different one of the plurality of tethers, and the first gripper means and the means for reciprocally moving it are used with each of the second gripper means in turn. For this purpose, the first gripper means and the means for reciprocally moving it may be mounted on a track extending between each of the second gripper means, so that the first gripper means, and the means for reciprocally moving it can be moved to each of the second gripper means as required for tensioning or slackening the tethers. Such an arrangement is especially advantageous when the tethers are arranged in groups since only one first gripper means need be provided for each group.Each of the second gripper means can be used to secure its tether to the tethered portion for as long as required.
A structure and methods of varying tension of a tether of a structure in accordance with the invention will now be described, by way of example, with reference to the accompanying drawings, in which:
Figure I shows diagrammatically a structure of the tension leg kind constructed in accordance with the invention;
Figure 2 shows a plan view of the structure shown in Figure 1;
Figure 3 shows means for varying the tension of a tether of the structure shown in Figure 1 on a larger scale;
Figure 4 shows diagrammatically a gripper device with its cover open;
Figure 5 is an end view of the gripper device in the direction A shown in Figure 4 with its cover closed;
Figure 6 shows diagrammatically means for varying the tension of a plurality of tethers in accordance with the invention;
Figure 7 is a side view of the apparatus shown in Figure 6; and
Figure 8 is a section through the apparatus of Figure 6 taken along the line
B-B shown in Figure 6.
Referring to the accompanying drawings, and initially to Figures 1 and 2, tethers 1 of a structure of the tension leg kind are each secured at one end to anchor means 2 and at the other end to a tethered portion indicated generally by the reference numeral 3 of the tension leg structure comprising a buoyant chamber 4 below the level of the water W and supported on it a platform 5 above the water level. Each group of a plurality of tethers 1 is provided with means for varying the tension in a tether, the said means being indicated generally by the reference numeral 6. As can be seen in more detail in Figure 3, the means 6 comprises first and second gripper devices indicated generally by the reference numerals 7 and 8, respectively, each being similar to that shown in Figures 4 and 5 and through each of which one of the tethers 1 passes.The second gripper device 8 is mounted on a base 9 having a channel 10 for the tether 1. The first gripper device 7 is mounted vertically above the second gripper device 8 on a cross-head 11 having a channel 12 to accommodate the tether.
The cross-head 11 is supported near each end on a pair of hydraulic rams 13 and 14, respectively, of the double-acting type having a powered return stroke connected to an hydraulic circuit (not shown) comprising a pump and a power unit for moving the cross-head 11 reciprocally upwardly and downwardly against a guide frame 15.
Referring to Figures 4 and 5, each of the gripper devices 7 and 8 comprises a casing 16 of generally U-shaped cross-section (see
Figure 5) which tapers in an axial direction.
Along each side, near its upper edge, the casing 16 is formed with a groove 16a. Two arms 16b extend from one side of the casing 16 and are formed with apertures to accommodate a hinge rod 16c. A cover 17 tapered similarly to the casing - l6 and also having two arms 17aformed with apertures is pivotally and slidably mounted on the hinge rod 16c. The cover 17 is formed along each side of its inner surface with a projection 17b arranged to mate with the groove 16a in the casing. To close the gripper device, the cover 17 is slid down the hinge rod 16c to the position shown in
Figure 4 so that its widest portion at the top is level with a slightly narrower portion of the casing 16.It is then pivoted over the casing 16 so that its projection 17b mates with the grooves 1 6a and locked by sliding up the hinge rod 1 6c until the widest portion of the cover 17 lies over the widest portion of the casing 16. The cover 17 can be opened by reversing this operation. A locking rod 17c (see Figure 3) is also provided to ensure that the cover 17 is locked in position. Within the casing 16 are two generally wedged-shaped gripper members 18 and 19, respectively, each having a groove 1 8a and 19cur, respectively, along the side adjacent to the other gripper member, to accommodate the tether 1.The gripper members 18 and 19 are each mounted on a row of roller bearings 20 and 21, respectively, lying between a bearing track 22 and 23, respectively, mounted in the casing 16 and a further bearing track 24 and 25, respectively, secured to each of the gripper members. Bearing retainers 26 (only one of which is shown) are arranged 1-o keep the bearings 20 and 21 in the correct position.
To the uppermost end of each gripper member 18 and 19 extends a lug 28 and 29, respectively, pivotally connected to a rod 30 and 31, respectively, of an hydraulic cylinder 32 and 33, respectively. These cylinders 32 and 33 can be operated either manually or automatically to withdraw the wedges 18 and 19 from the casing 16 by a small amount. Because of the taper of the wedges and of the casing, as the wedges are withdrawn they are moved farther apart either for the tether 1 to be inserted or removed from the grooves 1 8a and 19a in the gripper members or for slackening the tension in the tether as explained hereinafter.On insertion of the tether 1, after it has been placed in the grooves 1 8a and 19a, the hydraulic cylinders 32 and 33 are operated again to replace the gripper members 18 and 19 in their operative positions in the casing 16. When in this position, the gripper members 18 and 19 allow the tether 1 to be pulled through the gripper device in the direction indicated by the arrow C but, when a force is applied to the tether 1 in the reverse direction D, grip the tether and prevent movement of the tether in that direction. As the force in the opposite direction is increased the wedgeshaped gripper members 18 and 19 hold the tether 1 more firmly. A mechanical linkage 34 is provided between the gripper members 18 and 19 to keep the gripper members operating together.
In operation, the covers 17 of the gripper devices 7 and 8 are opened and the hydraulic cylinders 32 and 33 used to withdraw the gripper members 18 and 19 and hold them apart while the tether 1 is inserted into the grooves 1 8a and 1 9a of both gripper devices in such a manner that a force on the tether tending to move it in the direction C or forward direction will increase the tension in the tether while a force tending to move it in the reverse direction D will decrease the tension and slacken the tether. The gripper members are then allowed to retain their operative positions and the cover 17 locked shut.
The hydraulic rams 13 and 14 are then caused to raise the cross-head 11 and the first gripper device 7. Since the gripper device 7 will not allow the tether to move relative to it in the direction D it grips the tether 1 and pulls it upwardly in the direction C increasing the tension in the tether, while the second gripper device 8 allows the tether to pass through it in the direction
C. When the hydraulic rams 13 and 14 reach the upper limit of their stroke they operate trip switches (not shown) which initiate the return of the rams. As they start to return, the second gripper - device 8 grips the tether 1 preventing the tether from moving in the opposite direction D and maintaining the tension in the tether.The first gripper device 7 allows relative movement of the tether 1 through it in the direction C as the first gripper device is returned to its original position by the hydraulic rams. Reciprocal movement of the hydraulic rams 13 and 14 is repeated so that the tension in the tether is progressively increased until the desired tension is achieved in the tether. The tension in the tether can be read off a gauge calibrated for this purpose in the hydraulic circuit or a load cell on the tether. The second gripper device 8 can be used to secure the tether 1 to the tethered portion while maintaining the desired tension in the tether.
To slacken the tether 1, the first gripper device 7 is moved slightly in an upward direction sufficient to release the tether from the second gripper device 8. The hydraulic cylinders 32 and 33 can now be operated to withdraw the gripper members 18 and 19 of the second gripper device 8 and maintain them apart to allow the tether to move relative to the second gripper device 8 in the reverse direction D. The first gripper device 7 is then lowered and, since the load is acting on the first gripper device 7, it is caused to grip the tether 1, thus moving the tether 1 in the direction D and decreasing the tension in it. Just before the first gripper device 7 reaches its lowermost position, the gripper members 18 and 19 of the second gripper means 8 are allowed to return to their operative positions so as to grip the tether 1 and the load is returned to the second gripper device 8.
The hydraulic cylinders 32 and 33 of the first gripper device 7 are then operated to release the gripper members 18 and 19 of that device and allow the device to be raised by the hydraulic rams 13 and 14 relative to the tether 1 back to its uppermost position. Just before the first gripper device 7 reaches its uppermost position its gripper members 18 and 19 are released so that they again grip the tether and the operation is repeated until the tether is slackened to the desired extent.
Referring now to Figures 6, 7 and 8 where the same reference numerals are used to indicate the same components as in
Figures 1 to 5, two further second gripper devices, 35 and 36, respectively, are each arranged to engage a further tether 1 of the tension leg structure, each of the further second gripper device being identical to the second gripper device 8. The guide frame 15, the hydraulic rams 13 and 14 and the first gripper means 7 are mounted on rails 37 so as to be movable between each of the second gripper devices 8, 35 and 36 to tension or slacken off any one of the tethers held by the second gripper devices, as desired. The second gripper devices 8, 35 and 36 can be used to secure the tethers to the tethered portion 3 for as long as desired.
As an example of suitable dimensions for means for varying the tension in a tether of 5" diameter rope, for a capacity of 600 tons weight at a maximum speed of movement of the gripper device 7 of 1 foot/minute using an hydraulic system having an operational pressure of 2000 p.s.i. approximately, each of the hydraulic rams should be of approximately 20 inches in diameter with a stroke of 18 inches. A prime mover arranged to supply 70 B.H.P. (assuming an overall efficiency of approximately 60%) is required and a pump capable of a volume displacement of 30 gallons/minute. Each of the gripper devices is approximately 6 feet high, the total height of the tensionvarying means being approximately 15 feet.
In the apparatus described above, each of the second gripper devices 8, 35 and 36 is fixed relative to the platform 5. Each second gripper device may, however, be arranged for reciprocal movement relative to the platform 5 similarly to the first gripper device 7, a further pair of hydraulic rams similar to the rams 13 and 14 being provided for this purpose. A continuous increase in tension in the tether 1 can then be achieved by arranging for the second gripper device 8, 35 and 36 to move in the reverse direction D while the first gripper device 7 is moving in the forward direction
C, and in the forward direction C while the first gripper device 7 is moving in the reverse direction D.Thus, the tension in the tether l is increased both by the first gripper device 7 when this is moving in the forward direction, and, while the first gripper device is moving in the reverse direction, by the second gripper device 8, 35 or 36.
WHAT WE CLAIM IS:
1. A structure which comprises a tethered portion comprising a buoyant chamber and a platform supported on the buoyant chamber, the structure also comprising anchor means, a plurality of tethers extending from the tethered portion to the anchor means, and means for varying the tension of at least one of the tethers comprising first and second gripper means for gripping the tether, each of the gripper means being arranged to allow relative movement between the gripper means and the tether such that the tether can move relative to the gripper means in a forward direction in which, in use, tension in the tether is increased but be capable of gripping the tether to prevent relative movement of the tether in the reverse direction, and means for moving the first gripper means reciprocally relative to the tethered portion in the forward and reverse directions, the arrangement being such that, in operation, when the first gripper means is moving in the forward direction it can grip the tether so that there is relative movement between the tether and the second gripper means and when the first gripper means is moving in the reverse direction the second gripper means can grip the tether so that there is relative movement between the tether and the first gripper means.
2. A structure as claimed in claim 1, wherein the second gripper means is fixed relative to the tethered portion.
3. A structure as claimed in claim 1, wherein the means for varying the tension comprises means for moving the second gripper means reciprocally relative to the tethered portion in the forward and reverse directions, the arrangement being such that when the first gripper means is moving in the forward direction the second gripper means is moving in the reverse direction and when the first gripper means is moving in the reverse direction the second gripper means is moving in the forward direction.
4. A structure as claimed in any one of claims 1 to 3, wherein the first gripper means is located vertically above the second gripper means.
5. A structure as claimed in any one of claims l to 4, wherein each of the first and second gripper means is such that it tends to grip the tether more firmly the greater the force on the tether urging it to move in the reverse direction.
6. A structure as claimed in any one of claims 1 to 5, wherein the means for reciprocally moving the first gripper means relative to the tethered portion and the means for reciprocally moving the second gripper means, when provided, comprises hydraulic means.
7. A structure as claimed in claim 6, wherein the hydraulic means comprises one or more hydraulic rams.
8. A structure as claimed in any one of claims 1 to 7, wherein the means for reciprocally moving the or each gripper means is operable manually to reverse the direction of movement each time the or each gripper means reaches the lirnits of its stroke.
9. A structure as claimed in any one of claims 1 to 7, wherein the means for reciprocally moving the or each gripper means is operable to reverse the direction of movement automatically each time the or each gripper means reaches the limits of its stroke.
10. A structure as claimed in claim 9, wherein trip switches are located at the limits of the stroke of the or each gripper means and are operable by the gripper means itself when it reaches the said limits.
11. A structure as claimed in claim 6 or claim 7, wherein a gauge is provided in the hydraulic means to give an indication of the tension in the tether.
12. A structure as claimed in any one of claims 1 to 10, wherein a load cell or a strain gauge is located on the tether to give an indication of the tension in the tether.
13. A structure as claimed in any one of claims 1 to 12, wherein the first and second gripper means are so arranged that they can be released to allow the tether to move in the reverse direction relative to the gripper means.
14. A structure as claimed in any one of claims 1 to 13, wherein one or more further means for varying the tension of a tether comprising first and second gripper means is or are provided, each for a different one of the plurality of tethers of the structure.
15. A structure as claimed in any one of claims 1 to 13, wherein one or more further second gripper means is or are provided,
**WARNING** end of DESC field may overlap start of CLMS **.
Claims (23)
1. A structure which comprises a tethered portion comprising a buoyant chamber and a platform supported on the buoyant chamber, the structure also comprising anchor means, a plurality of tethers extending from the tethered portion to the anchor means, and means for varying the tension of at least one of the tethers comprising first and second gripper means for gripping the tether, each of the gripper means being arranged to allow relative movement between the gripper means and the tether such that the tether can move relative to the gripper means in a forward direction in which, in use, tension in the tether is increased but be capable of gripping the tether to prevent relative movement of the tether in the reverse direction, and means for moving the first gripper means reciprocally relative to the tethered portion in the forward and reverse directions, the arrangement being such that, in operation, when the first gripper means is moving in the forward direction it can grip the tether so that there is relative movement between the tether and the second gripper means and when the first gripper means is moving in the reverse direction the second gripper means can grip the tether so that there is relative movement between the tether and the first gripper means.
2. A structure as claimed in claim 1, wherein the second gripper means is fixed relative to the tethered portion.
3. A structure as claimed in claim 1, wherein the means for varying the tension comprises means for moving the second gripper means reciprocally relative to the tethered portion in the forward and reverse directions, the arrangement being such that when the first gripper means is moving in the forward direction the second gripper means is moving in the reverse direction and when the first gripper means is moving in the reverse direction the second gripper means is moving in the forward direction.
4. A structure as claimed in any one of claims 1 to 3, wherein the first gripper means is located vertically above the second gripper means.
5. A structure as claimed in any one of claims l to 4, wherein each of the first and second gripper means is such that it tends to grip the tether more firmly the greater the force on the tether urging it to move in the reverse direction.
6. A structure as claimed in any one of claims 1 to 5, wherein the means for reciprocally moving the first gripper means relative to the tethered portion and the means for reciprocally moving the second gripper means, when provided, comprises hydraulic means.
7. A structure as claimed in claim 6, wherein the hydraulic means comprises one or more hydraulic rams.
8. A structure as claimed in any one of claims 1 to 7, wherein the means for reciprocally moving the or each gripper means is operable manually to reverse the direction of movement each time the or each gripper means reaches the lirnits of its stroke.
9. A structure as claimed in any one of claims 1 to 7, wherein the means for reciprocally moving the or each gripper means is operable to reverse the direction of movement automatically each time the or each gripper means reaches the limits of its stroke.
10. A structure as claimed in claim 9, wherein trip switches are located at the limits of the stroke of the or each gripper means and are operable by the gripper means itself when it reaches the said limits.
11. A structure as claimed in claim 6 or claim 7, wherein a gauge is provided in the hydraulic means to give an indication of the tension in the tether.
12. A structure as claimed in any one of claims 1 to 10, wherein a load cell or a strain gauge is located on the tether to give an indication of the tension in the tether.
13. A structure as claimed in any one of claims 1 to 12, wherein the first and second gripper means are so arranged that they can be released to allow the tether to move in the reverse direction relative to the gripper means.
14. A structure as claimed in any one of claims 1 to 13, wherein one or more further means for varying the tension of a tether comprising first and second gripper means is or are provided, each for a different one of the plurality of tethers of the structure.
15. A structure as claimed in any one of claims 1 to 13, wherein one or more further second gripper means is or are provided,
each for a different one of the plurality of tethers, and the first gripper means and the means for reciprocally moving it is so arranged that it can be used with each of the second gripper means in turn.
16. A structure as claimed in claim 15, wherein the first gripper means and the means for reciprocally moving it are mounted on a track extending between each of the second gripper means so that the first gripper means and the means for reciprocally moving it can be moved to each of the second gripper means.
17. A method of increasing tension of a tether extending from a tethered portion, comprising a buoyant chamber and a platform supported on it, to anchor means, of a structure, which method comprises engaging the tether in first and second gripper means each of the gripper means being arranged to allow relative movement between the gripper means and the tether such that the tether can move relative to the gripper means in a forward direction in which tension in the tether is increased but be capable of gripping the tether to prevent relative movement of the tether in the reverse direction, moving the first gripper means reciprocally relative to the tethered portion in the forward and reverse directions so that when the first gripper means is moving in the forward direction it grips the tether and there is relative movement between the tether and the second gripper means and when the first gripper means is moving in the reverse direction the second gripper means grips the tether and there is relative movement between the tether and the first gripper means.
18. A method as claimed in claim 17, wherein as the first gripper means is moved reciprocally relative to the tethered portion the second gripper means remains stationary relative to the tethered portion.
19. A method as claimed in claim 17, which comprises moving the second gripper means reciprocally relative to the tethered portion in the forward and reverse directions so that when the first gripper means is moving in the forward direction the second gripper means is moving in the reverse direction and when the first gripper means is moving in the reverse direction, the second gripper means is moving in the forward direction.
20. A method of decreasing tension of a tether extending from a tethered portion, comprising a buoyant chamber and a platform supported on it, to anchor means, of a structure, which method comprises engaging the tether in first and second gripper means, each of the gripper means being arranged to allow relative movement between the gripper means and the tether such that the tether can move relative to the gripper means in a forward direction in which tension in the tether is increased but be capable of gripping the tether to prevent relative movement of the tether in the reverse direction, each of the gripper means also bring so arranged that it can be released to allow the tether to move in the reverse direction relative to the gripper means, and the tension in the tether is decreased by releasing the second gripper means and moving the first gripper means, which grips the tether, in the reverse direction, causing the second gripper means to grip the tether, releasing the first gripper means and moving the first gripper means in the forward direction relative to the tether.
21. A structure as claimed in claim 1 and substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.
22. A method of increasing tension of a tether as claimed in claim 17 and substantially as hereinbefore described with reference to the accompanying drawings.
23. A method of decreasing tension of a tether as claimed in claim 20 and substantially as hereinbefore described with reference to the accompanying drawings.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB827276A GB1585123A (en) | 1977-05-31 | 1977-05-31 | Structures having buoyant chambers |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB827276A GB1585123A (en) | 1977-05-31 | 1977-05-31 | Structures having buoyant chambers |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| GB1585123A true GB1585123A (en) | 1981-02-25 |
Family
ID=9849317
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB827276A Expired GB1585123A (en) | 1977-05-31 | 1977-05-31 | Structures having buoyant chambers |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB1585123A (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0072692A2 (en) * | 1981-08-17 | 1983-02-23 | Conoco Phillips Company | Controlling the tension in platform supporting tension legs |
| GB2160278A (en) * | 1984-06-12 | 1985-12-18 | Vickers Plc | Adjusting axial length of a marine platform tether line |
| DE3733952A1 (en) * | 1987-10-08 | 1989-04-20 | Ruhrgas Ag | METHOD AND DEVICE FOR SETTING UP AN OFFSHORE SYSTEM |
-
1977
- 1977-05-31 GB GB827276A patent/GB1585123A/en not_active Expired
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0072692A2 (en) * | 1981-08-17 | 1983-02-23 | Conoco Phillips Company | Controlling the tension in platform supporting tension legs |
| EP0072692A3 (en) * | 1981-08-17 | 1984-06-06 | Conoco Inc. | Controlling the tension in platform supporting tension legs |
| GB2160278A (en) * | 1984-06-12 | 1985-12-18 | Vickers Plc | Adjusting axial length of a marine platform tether line |
| DE3733952A1 (en) * | 1987-10-08 | 1989-04-20 | Ruhrgas Ag | METHOD AND DEVICE FOR SETTING UP AN OFFSHORE SYSTEM |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PS | Patent sealed | ||
| PCNP | Patent ceased through non-payment of renewal fee |