US3563042A

US3563042A - Encapsulated cable system for anchoring a floating platform

Info

Publication number: US3563042A
Application number: US808599A
Authority: US
Inventors: Carroll John Ryan
Original assignee: Lockheed Aircraft Corp
Current assignee: Canocean Resources Ltd
Priority date: 1969-03-19
Filing date: 1969-03-19
Publication date: 1971-02-16
Anticipated expiration: 1988-02-16

Abstract

AN ENCAPSULATED CABLE ANCHORING AND TENSIONING SYSTEM IS PROVIDED FOR MAINTAINING A FLOATING PLATFORM ON LOCATION WITH RESPECT TO AN UNDERWATER INSTALLATION. THE PLATFORM IS MAINTAINED ON LOCATION BY APPLYING DESIRED TENSION TO A PLURALITY OF CABLES AND THEIR ASSOCIATED ENCAPSULATING TUBING. THE SYSTEM INCLUDES METHOD AND APPARATUS FOR INSTALLING, PRELOADING, ADJUSTING AND REMOVING THE ENCAPSULATED CABLE ASSEMBLIES. THE ENCAPSULATING TUBES PROVIDE A MEANS OF REDUCING BENDING LOADS IN THE ASSEMBLY AND ALSO PROTECT THE CABLES AGAINST CORROSION, ETC.

Description

Feb. 16, 1971 c, N 3,563,042

ENCAPSULATED CABLE SYSTEM FOR ANCHORING A FLOATING PLATFORM Filed March 19, 1969 5 Sheets-Sheet 1 11A F l'l! CARROLL JOHN RYAN Attorney Feb. 16, 1971 c. J. RY AN ENCAPSULATED CABLE SYSTEM FOR ANCHORING A FLOATING PLATFORM Filed March 19, 1969 5 Sheets-Sheet S 3 E l l Q lh. l

96 1', ,77 I 1111 III IIITrr DmMVe4 4O Attorney C. J. RYAN Feb. 16, 1971 ENCAPSULATED CABLE SYSTEM FOR ANCHORING A FLOATING PLATFORM Filed March 19, 1969 5 Sheets-Sheet 4.

INVIEN'I'OQR.

Attorney CARROLL JOHN RYAN gent $411141 7% o o m o m a M c. J. RYAN 3,563,042

ENCAPSULATED CABLE SYSTEM FOR ANCHORING A FLOATING PLATFORM Feb. 16, 1971 5 Sheets-Sheet 5 Filed March 19, 1969 g &

FIG.6

INVIL'N'I'OR. CARROLL JOHN RYAN gent 4171,64 Attorney United States Patent Oflice 3,563,042 Patented Feb. 16, 1971 US. Cl. 61-46.5 24 Claims ABSTRACT OF THE DISCLOSURE An encapsulated cable anchoring and tensioning system is provided for maintaining a floating platform on location with respect to an underwater installation. The platform is maintained on location by applying desired tension to a plurality of cables and their associated encapsulating tubing. The system includes method and apparatus for installing, preloading, adjusting and removing the encapsulated cable assemblies. The encapsulating tubes provide a means of reducing bending loads in the assembly and also protect the cables against corrosion, etc.

BACKGROUND OF THE INVENTION The present invention relates to underwater equipment, such as oil well equipment for use at off-shore locations, and pertains more particularly to a deep water system for anchoring and tensioning a floating platform to maintain the floating platform on location with respect to an underwater installation.

Heretofore, off-shore oil and gas field operations and the like ordinarily have required a fixed foundation for drilling and production operations. However, the cost of a tower or other available type of artificial island increases rather rapidly as the water depth increases, while available technology and equipment limits conventional type of installations to areas of relatively shallow water. For example, existing installations may currently reach to a water depth of the order of 200-250 ft.

In some instances, floating vessels have provided suitable foundations for conducting drilling and completion operations in water depths of more than 350 ft. Generally speaking these prior art floating platforms have comprised a buoyant platform which is tethered to the water floor on a fixed pipe arrangement. One of the problems with this type of floating platform resides in the large stress concentrations due to the bending moment at the bottom and top connections of the fixed pipe to the water floor. Such prior art assemblies are quite susceptible to stress failures and in addition there is a serious problem of aligning each pipe precisely with respect to the remaining pipes so that the aforementioned stresses are not unequal. In addition to the aforementioned design problems such prior art floating platforms are very difficult to install on location and are almost impossible to maintain and inspect after installation.

One of the principal objects of the present invention is the provision of an encapsulated cable anchoring and tensioning system which will reduce the bending loads associated with prior art floating platform systems.

Another object of the invention is to provide an encapsulated cable anchoring and tensioning system which will protect the cable against corrosion, etc.

A further object of the invention is the provision of encapsulated cable anchoring and tensioning system for a floating platform which may be easily installed and adjusted as well as providing a system in which the encapsulated cable assembly may be periodically inspected and easily replaced if necessary.

Other and further objects and advantages of the present invention will be apparent from the following description and claims and are illustrated in the accompanying drawings which, by way of illustration, show preferred embodiments of the present invention and the principles thereof and what are now considered to be the best modes contemplated for applying these principles. Other embodiments of the invention embodying the same or equivalent principles may be used and structural changes may be made as desired by those skilled in the art without departing from the present invention and the purview of the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an overall schematic view, partially in section, illustrating the major components of an exemplary embodiment of an encapsulated cable anchoring and tensioning system constructed in accordance with the principles of the present invention;

FIG. 2 is a longitudinal view, partially in section, illus trating one embodiment for anchoring and sealing an encapsulated cable at an underwater template;

FIGS. 3A and 3B are a longtiudinal view, partially in section, illustrating structural details of certain assemblies located at the floating platform for installing and maintaining the encapsulated cable system under the desired tension;

FIG. 4 is a schematic view illustrating the application of a guide trumpet arrangement which reduces stress concentrations caused by bending loads imparted during the operation of maintaining the floating platform on location with respect to an underwater installation;

FIGS. 5A and 5B illustrate a modified embodiment of a cable anchoring and tensioning system constructed in accordance with the principles of the present invention; and

FIG. 6 is a side elevation of a ball seal connecting joint between the cable head and the encapsulating tubing of the embodiment shown in FIGS. 5A and 5B.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 is an overall side elevation, partially in section, illustrating the major components of the encapsulated cable anchoring system of the present invention. In FIG. 1 a floating platform is indicated generally by the numeral 12 and above the surface of a body of water 13. The floating platform is provided with an upper or main deck 14 and is also equipped with a plurality of floats or buoyant pontoon means 16 which support the deck structure of the platform 12 by Way of support members 18 which are suitably cross braced by

structural members

20 and 22.

Located on the water floor 24 are one or more anchoring templates 26 which are secured to the water floor by means of suitable piling members such as shown at 28. The anchoring template was initially lowered down to the water floor 24 from a floating platform on guide structures such as guide lines 54. The location of the guide lines 54 may be maintained by attaching buoys to the upper ends which float on the water surface 13. The floating platform 12 is anchored to the template or templates 26 by means of an encapsulated cable system shown generally at 30.

The major components of the encapsulated cable anchoring system comprise an encapsulating tube 32 which is provided at its lower end with a cannister like sealing element 34. The cannister seal 34 engages a probe element 36 associated with the template 26 in a sealed manner as will be described in greater detail at a later point in the description. The encapsulating tube 32 extends upwardly from the template 26 through the buoyant pontoon element 16 and the support 18 to the deck structure 14 of the floating platform 12 where the upper end 38 of the encapsulating tube 32 is firmly secured. A tensioning cable or flexible line 40 extends downwardly from a cable reel mechanism 42 through the encapsulating tube 32 to the probe 36 at the template 26 where it is suitably secured in a manner which will be described in greater detail at a later point in the description.

The location of the floating platform 12 with respect to the underwater template or templates 26 may be accurately controlled by the application of suitable tension to the tensioning cables 40. In actual practice there may be a great number of such encapsulated cable devices 30 and in any event there should preferably be at least three such devices in order to keep the floating platform on location. Suitable flow lines 44 which produce well fluids from underwater wells (not shown) may be suitably secured to the tensioning means 30 as by clamps 46. These flowlines 44 then lead upwardly to oil and gas production and storage facilities on the deck 14 as indicated generally by the reference numeral 48.

Referring now to FIG. 2 in conjunction with FIG. 1, the operation of lowering and securing the encapsulated cable anchoring and tensioning system to the ocean floor template 26 will be described. At the deck structure 14 of the platform 12 the encapsulating tubing 32. is connected in sections as by welding or other suitable coupling devices and lowered down through the interior of structural member 18 out through the lower end of the buoyant pontoon member 16. If the opening through the structural member 18 is large enough, the cannister seal element 34 may be passed therethrough on the downstream end of the encapsulating tubing member 32. However, if the cannister seal element 34 is too large to pass through the opening in structural member 18 then a diver descends from the water surface 13 to a position below the pontoon 16 and suitably secures the cannister seal 34 to the downstream end of the encapsulating tube 30.

As shown in FIG. 2 the cannister seal element is provided with guide shoes 52' which fit about the guide lines 54 which extend from the bottom of the pontoon elements 16 down to the ocean floor template 26. These guide elements insure that the cannister seal will be properly guided into position over the template probe 36.

The lower end of the cannister seal element 34 is provided with a generally flared mouth 56 which insures that the cannister seal element 34 is properly guided into the probe element 36. During the lowering of the encapsulated tube 30 and cannister element 34 sea water is permitted to enter through the flared mouth 56 into an internal chamber 58 and thence upwardly through the cable tube 30.

The sealing element of the cannister seal 34 comprises a flexible, pressure-sensitive diaphragm seal 60 which is forced over the upper end 62 of the probe 36 as the cannister is moved downwardly over the probe. A second chamber 64 is formed in the cannister 34 radially outwardly of the flexible seal diaphragm 60. Sea water communicates with the chamber 64 by means of inlet openings such as shown at 66.

After the cannister seal element has been moved downwardly over the probe 36 to the position shown in FIG. 2, sea water is evacuated from the cannister chamber 58 and from the cable tube 30 by means of a pump located at the deck 14 of the floating platform 12. Since the very high pressure ambient sea water is positively acting on the radially outer side of the flexible seal diaphragm 60 via chamber 64, a very firm fluidtight seal is established in the area 68 between the probe 36 and the flexible diaphragm 60. After the seal has been established at the probe 36 a sealed tubing extends from the ocean floor template 26 upwardly to the deck structure 14 of the floating platform 12.

An operator on the deck 14 now begins to reel an anchoring and tensioning cable 40 downwardly hrough the encapsulating cable tube 32 toward the template probe 36. As shown in FIG. 2 the template probe 36 is provided internally with a flared mouth trumpet element 70 which gradually tapers into a concentric guide tube in the area denoted at 72. At the very bottom of the trumpet guiding tube 72 an internally threaded nut element 74 is provided for threadably receiving a threaded nose portion 76 formed on the downstream end of a weighted cable head 78.

A torque tube 80 is fixedly secured to the cable head 78 and extends upwardly through a sliding seal element 82 where its upper end terminates in a torque head 84. In order to secure the anchoring and tensioning cable 40 inside the threaded nut 74 formed in the base of the trumpet guide tube 72, a torque tool 88 is fed downwardly over the cable 40 until a wrench element 90 on the tool 88 engages the torque head 84. The torque tool 88 is then rotated thereby causing the torque tube 80 and cable head 78 to rotate which causes the threaded end 76 to be securely fastened inside the threaded nut 74. The torque tool 88 may then be recovered at the floating platform 12. At this juncture the anchoring and tensioning cable 40 is securely anchored at the template 26 and the cable is encapsulated inside the protective tubing 32.

Referring now to FIGS. 3A and 3B it may be observed that the encapsulating tube 32 extends upwardly through the pontoon 16 and support member 18 to a secondary deck area 15 near the top of the floating platform 12. A permanent support structure 96 is formed on the deck 15 and has associated therewith a tube hanging support 98 and a split-sleeve cable centering block 99.

The tube hanging support 98 is provided with a coneshaped tapered wall 100 which is adapted to receive a plurality of split-sleeve locking grip members 102. The locking grips 102 have tapered outer walls 104 which slidably mate with the tapered wall 100 of the cone-shaped portion of the tube hanging support. The inner walls of the locking grips 102 are provided with a saw-tooth locking surface 106 which is adapted to bite into the encapsulating tubing 32 and holds the tubing 32 against movement.

If a downward force is exerted on the encapsulating tubing 32, the tapered support surface 100 and the tapered gripper surface 104 serve to wedge the gripper 102 radially inwardly into even tighter engagement with the encapsulating tube 32 thereby preventing movement of the tube 32 downwardly through the support member 18. However, if additional upwardly directed tension is exerted on the cable 40 the encapsulating tubing may move upwardly whereby the locking grips 102 will become temporarily inactive.

After the cable 40 has been anchored at the template probe 36 and the torque tool 88 has been recovered, the cable is removed from the reel 42 and threaded through a cable anchoring and tensioning assembly generally shown at 110. The cable anchoring and tensioning assembly 110 is then secured in place on the support structure 96 as by means of bolts 112 which pass through the flanged ends of a plurality of support posts 114. The upper ends of the posts 114 are permanently secured to a main support plate 116 of the assembly 110.

A first cable gripping element 118 which may be selectively actuated to tightly grip around the cable and hold the same against movement in a manner well-known in the art is provided on the support 96. The cable grip 118 does not move during operation of the assembly 110 and remains in the position shown in FIG. 3A.

Mounted on top of the support plate 116 is a doubleacting jack assembly having a piston 120 slidably received inside a cylinder 122. An upper rod portion 124 and a lower rod portion 126 extend from each side of the piston 120 and sealingly protrude through the end walls of the cylinder 122 regardless of the position of the piston 120. The

piston rod portions

124 and 126 are hollow so that the cable 40 may extend therethrough.

Fluid ports

128 and 130 are provided in the cylinder housing 122 so that pressure fluid may be admitted from a suitable source (not shown) to actuate the piston 120 either upwardly or downwardly within the cylinder 122. A second cable gripping device 130 is provided on the upper end of the piston rod 124 and is in all respects identical with the cable gripping device 118 previously described.

The operation of the cable anchoring and tensioning assembly 110 will now be described. The piston 120 is initially moved to the lowermost portion of the cylinder 122. The cable gripping mechanism 130 is then actuated to tightly grip about the upper end of the cable 40. The lower cable gripping mechanism 118 is moved to an unlocked position so that the cable 40 may freely pass therethrough.

Pressure fluid is then admitted to the cylinder 122 through the port 130 thereby moving the piston 120 and associated upper gripper element 130 to the position shown in FIG. 3A. This operation increases the tension in the cable 40 and this increase in tension may be measured at a first load cell or strain gauge such as shown at 136.

If more tension is desired in the cable 40 the lower gripping device 118 is actuated to tightly lock about the cable 40 and the upper cable gripper mechanism 130 is released so that the

rod members

124 and 126 may slide downwardly with respect to the cable. Pressure fluid is then admitted to the port 128 which moves the piston 120 and associated rod elements downwardly to the lowermost position within the cylinder 122. The operation is now repeated whereby the lower cable gripping element 118 is released and the upper cable gripping element is actuated to tightly grip the cable after which the piston 120 is again moved upwardly within the cylinder 122 until such time as the desired tension is established as measured at the load cell 136.

Once the desired tension has been established in the cable 40 the cable may be permanently held in the area of the lower gripping means 118 and the entire cable anchoring and tensioning assembly 110 may be removed. After the desired tension has been established in the cable 40 a preservative type colloidal fluid is pumped down the encapsulating tubing 32 to completely surround the cable 40 and thereby prevent corrosion thereof. The preservative type fluid is preferably heavier than water so as to force any water in the tubing 32 out the top of the tubing. The desired tension can be monitored by a second load cell or strain gauge such as shown at 137.

The permanent support structure 96 located on the deck is provided with a strain gauge spool assembly 140 which may be continuously monitored at an instrument panel on the platform 12 to check the tension in the cable 40. Thus, if conditions dictate the cable anchoring and tensioning assembly 110 may be re-installed to either increase or decrease the tension in the cable 40.

From tim to time it may be necessary to inspect, repair or replace any one of the many cables 40 which will be utilized to keep the platform on location. This may be easily accomplished by running the torque tool 88 down the encapsulating tubing 32 and releasing the cable head 78 from the threaded nut 74 at the bottom of template probe 36.

Turning now to FIG. 3B it can be observed that a flared mouthed trumpet element 144 gradually tapers into a concentric guide tube in the area 146. Thus upper trumpet guiding element 144 has a lowermost portion which protrudes from the bottom of the pontoon element .16. Thus, the encapsulating tube 32 containing the anchoring and tensioning cable 40 is provided with a flared mouthed trumpet element 70 at its lower end (FIG. 2) and a similar trumpet element 144 at its upper end (FIG. 3B). The purpose of the flared mouth trumpet guide elements is to reduce the local bending loads in the encapsulating tubing 32 when the floating platform 12 is moved ofl location with respect to the template 26.

FIG. 4 is a schematic illustration showing the bending loads that are introduced into the encapsulating tubing 32 when the floating platform 12 is moved laterally off location with respect to the template 26. As may be easily observed with reference to FIG. 4, the flared mouth of the trumpet guide elements 70 and 144- is designed to give a constant stress level at all vertical sections of the tubing 32 which are under bending stress. Thus the flared mouth trumpet guide elements provide an important aspect of the invention since the encapsulating tubing 32 might easily rupture under local bending loads if the flared mouth were not provided to properly distribute such loads.

Referring back to FIG. 3B it may be noted that a flexible boot has its upper end attached to the lower end of the guide trumpet 144 just below the buoyant pontoon 16. A slip joint seal element 152 is formed on the lower end of the boot 150 to establish a sliding seal between the boot and the encapsulating tubing 32. The purpose of the flexible boot 150 with the sliding seal .152 is to prevent the escape of any anti-corrosive fluid which may be supplied to the area between the outside of the encapsulating tubing 32 and the inside of the structural member 18.

FIGS. 5A and 5B illustrate a modified embodiment of the invention wherein the encapsulating tubing 32 and the cable 40' may be lowered down into engagement with the template probe 36' in a single operation. As shown in FIG. SE a special cable head is provided on the downstream end of the cable 40'. The cable head 160 is pro vided with a lower externally threaded end portion 162 which is adapted to threadedly engage an internally threaded portion 164 formed in the lower end of the template probe 36. The cable head 160 is also provided with one or more sealing elements 166 which are adapted to sealingly engage the cable head 160 with the internal annular wall of the template probe 36 in a fluidtight manner.

The upper portion 168 of the cable head 160 is gen erally ball shaped and is provided with a flared mouth trumpet opening 170 in the top thereof. The lower portion of the encapsulating tubing 32 is connected to the ball portion 168 of the cable head 160 by means of pins 174 which fit in oversized openings 176 formed in the ball shaped member 168 as best shown in FIG. 6. The purpose of the oversized openings 176 is to permit a sealed ball type joint 178 to be established between the lower end of the encapsulating tubing 32' and the upper end of the cable head 160 and still permit swivel action movement between these two elements.

Suitable guide shoes 52' fit about guide lines 54' which extend from the bottom of the pontoon element .16 down to the ocean floor template 26'. These guide elements ensure that the cable head 160 is properly guided into position inside the template probe 36. An electrical lead 180 extends from the floating platform down to explosive bolt elements 182 associated with the guide shoes 52'.

The explosive bolt elements 182 may be actuated by passing current through the electrical lead 180 which severs the connection between the guide elements 52' and the encapsulating tube 32' and associated cable head 160. After the encapsulating tubing 32' with the specially constructed cable head 160 has been guided into the position shown in the lower portion of FIG. 5 the explosive bolts 182 are actuated to disconnect the encapsulating tube and the cable head from the guide frame and shoe elements 52'. At this stage in the operation a torquing force is applied at the floating platform 12 which rotates both the encapsulating tubing 32' and the cable head 160 to cause the threaded end .162 of the cable head to threadedly engage the threaded portion 164 in the base of the template probe 36'.

After the encapsulating cable has been installed, as described above, the upper end portion of the encapsulating tubing 32' is provided with a ball joint and slip tube assembly as shown generally at 186 in FIG. 5A. The ball joint is denoted generally at 178' and is in all respects identical with ball joint assembly 178 established between the cable head .160 and the lower end of the encapsulating tubing 32. A sliding seal 190 is established between the support member 18 and the upper end of the encapsulating tubing 32 to provide for movement of the tubing as tension is either increased or decreased in the cable 40' as conditions at the floating platform dictate. In all other respects the embodiment of FIGS. A and 5B operates in a manner similar to that described with respect to the embodiment of FIGS. 1-4. As with the embodiment depicted in FIGS. 14 a preservative type fluid may be placed in the area between the cable 40 and the internal wall of the encapsulating tubing 32' to prevent corrosion of the cable.

While I have illustrated and described preferred embodiments of my invention, it is to be understood that these are capable of variation and modification, and I therefore do not wish to be limited to the precise details set forth, but desire to avail myself of such changes and alterations as fall within the purview of the following claims.

What is claimed is:

1. A method of maintaining a floating platform on location with respect to an underwater installation, said method comprising:

establishing an underwater anchoring template on the water floor in the area of the underwater installation; moving a floating platform to a position on the water surface above the anchoring template and establishing guide means between the floating platform and the template; lowering an anchoring and tensioning cable and an encapsulating tubing therefor down the guide means from the platform into engagement with the template to establish an encapsulated cable anchoring and tensioning assembly between the platform and the template; applying suitable tension to the encapsulated cable assembly to maintain the platform at a desired surface location with respect to the underwater installation;

establishing a fluidtight sealed connection at the template for the encapsulated cable assembly; and admitting corrosion resistant fluid into the encapsulat' ing tubing to surround the encapsulated cable between the template and the platform.

2. A method as set forth in claim 1 wherein said corrosion resistant fluid is colloidal and heavier than water.

3. A method as set forth in claim 1 wherein said encapsulating tubing is lowered from the platform into engagement with the template in one operation and the anchoring and tensioning cable is lowered down through the encapsulating tubing into engagement with the template in a second operation.

4. A method as set forth in claim 3 wherein a plurality of encapsulated cable anchoring and tensioning assemblies are established between the platform and the anchoring template.

5. A method as set forth in claim 3 wherein said cable is provided with a rotatable head portion and is engaged to the template by rotating said cable head.

6. A method of maintaining a floating platform on location with respect to an underwater installation, said method comprising:

establishing an underwater anchoring template on the water floor in the area of the underwater installation;

moving a floating platform to a position on the water surface above the anchoring template and establishing guide means between the floating platform and the template;

lowering an anchoring and tensioning cable and an encapsulating tubing therefor down the guide means from the platform into engagement with the template to establish an encapsulated cable anchoring and tensioning assembly between the platform and the template; applying suitable tension to the encapsulated cable assembly to maintain the platform at a desired surface location with respect to the underwater installation;

establishing a fluidtight seal between the encapsulating tubing and the template; and wherein said fluidtight seal is established by means of a flexible diaphragm seal which is actuated by reducing the water pressure inside the encapsulating tubing to permit the ambient water pressure at said template to act against the outer wall of the diaphragm seal to force said wall into tight engagement with a portion of the template.

7. A method as set forth in claim 6 wherein a corrosion resistant fluid is admitted into the encapsulating tubing to surround the encapsulating cable between the template and the platform.

8. A method as set forth in claim 7 wherein the corrosion resistant fluid is colloidal and heavier than water.

9. An encapsulated cable anchoring and tensioning system for maintaining a floating platform on location with respect to an underwater installation comprising:

an anchoring template secured to the water floor in the area of the underwater installation;

a floating platform located on the water surface above the template;

an anchoring and tensioning cable having a first end connected to the floating platform and a second end connected to the template;

an encapsulating tubing surrounding the cable and extending from the platform to the template;

means establishing a fluidtight seal between the encapsulating tube and the second end portion of the cable at the template;

means at the platform for applying tension to the encapsulated cable assembly to maintain the platform at a desired location with respect to the template and the underwater installation; and a corrosion resistant fluid placed in the encapsulating tubing to surround the encapsulated cable between the template and the platform.

10. An encapsulating cable and anchoring tensioning system as set forth in claim 9 wherein the corrosion resistant fluid is colloidal and heavier than water.

11. An encapsulated cable anchoring and tensioning system for maintaining a floating platform on location with respect to an underwater installation comprising:

a floating platform located on the water surface above the template;

means establishing a fluidtight seal is established between the encapsulating tube and the second end portion of the cable at the template;

means at the platform for applying tension to the encapsulated cable assembly to maintain the platform at a desired location with respect to the template and the underwater installation, and wherein said template is provided with an upwardly projecting probe element and the lower end of said encapsulating tubing is provided with a generally bell-shaped cannister element adapted to fit over the template probe, an annular flexible diaphragm seal element contained within said cannister, means communicating the radially outward side of said diaphragm seal with the ambient water pressure whereby reduction of the pressure inside said encapsulating tubing causes the ambient water pressure to force the diaphragm seal element into fluidtight engagement with the outer wall of the template probe. 12. An encapsulated cable anchoring and tensioning system as set forth in claim 11 wherein a corrosion resistant fluid is placed in the encapsulating tubing to surround the encapsulated cable between the template and the platform.

13. An encapsulated cable anchoring and tensioning system as set forth in claim 12 wherein said corrosion resistant fluid is colloidal and heavier than water.

14. An encapsulated cable anchoring and tensioning system for maintaining a floating platform on location with respect to an underwater installation comprising:

a floating platform located on the water surface above the template;

means at the platform for applying tension to the encapsulated cable assembly to maintain the platform at a desired location with respect to the template and the underwater installlation; and wherein the second end of the cable is provided with a cable head having actuating means for engaging the template, and removable activating means are provided in the en capsulating tubing for actuating the cable head into engagement with the template.

15. An encapsulated cable anchoring and tensioning system as set forth in claim 14 wherein the cable head is rotatable and has a threaded end portion for engaging said template and wherein said activating means comprises a tubular torquing tool which is passed over the cable and extends downwardly from the floating platform to the cable head.

16. An encapsulated cable anchoring and tensioning system for maintaining a floating platform on location with respect to an underwater installation comprising:

a floating platform located on the water surface above the template;

an encapsulating tubing surrounding the cable and extending from the platform to the template; and wherein the anchoring and tensioning cable and the encapsulating tubing are connected to each other at the second end of the cable so as to comprise a unitary structure;

means at the platform for applying tension to the encapsulated cable assembly to maintain the platform at a desired location with respect to the template and the underwater installation; and wherein the second end of the cable is provided with a cable head having a sealed ball joint assembly formed on a first end of the cable head to provide a sealed connection between the encapsulating tubing and the cable head, which sealed connection permits limited swivel movement between the encapsulating tubing and the cable head.

17. An encapsulated cable anchoring and tensioning system as set forth in claim 16 wherein connecting means are provided between the second end of the cable head and the encapsulating tubing so that a continued rotative force applied to the tubing will be transmitted to the cable head to cause rotation of the cable head.

18. An encapsulated cable anchoring and tensioning system as set forth in claim 17 wherein a second end of the cable head is provided with a threaded member for 10 engaging a mating threaded member formed on the template.

19. An encapsulated cable anchoring and tensioning system for maintaining a floating platform on location with respect to an underwater installation comprising:

a floating platform located on the water surface above the template;

means at the platform for applying tension to the encapsulated cable assembly to maintain the platform at a desired location with respect to the template and the underwater installation, and wherein said means for applying tension to the encapsulated cable assembly comprises:

a double-acting fluid actuated jack having a piston received in a cylinder;

a hollow rod extending through the piston and protruding from each end of the cylinder;

first selectively operable cable gripping means located on one side of said jack;

second selectively operable cable gripping means located on the other side of the jack;

said cable extending through said hollow rod and both said cable gripping means; whereby said jack may be operated in cooperation with selective actuation of said cable gripping means to increase or decrease the tension in the cable.

20. An encapsulated cable anchoring and tensioning 35 system as set forth in claim 19 wherein a plurality of encapsulating cable assemblies are established between the platform and the anchoring template and the doubleacting jack assembly for applying tension to the cable comprises a removable unit which may be selectively at- 40 tached to any given encapsulated cable assembly.

21. An encapsulated cable anchoring and tensioning system as set forth in claim 19 wherein tensioning measuring means for determining the tension in said cable is operatively associated with the double-acting jack assembly.

22. An encapsulated cable anchoring and tensioning system as set forth in claim 19 wherein one of said cable gripping means is operatively associated with the platform to securely hold the cable under a preselected tension 50 and wherein tension measuring means are operatively associated with said cable gripping means so that the tension in the cable may be continuously monitored.

23. An encapsulated cable anchoring and tensioning system for maintaining a floating platform on location with respect to an underwater installation comprising:

an anchoring template secured to the water floor in the area of the underwater installation; a floating platform located on the water surface above the template; an anchoring and tensioning cable having a first end connected to the floating platform and a second end connected to the template; an encapsulating tubing surrounding the cable and eX- tending from the platform to the template; means at the platform for applying tension to the encapsulated cable assembly to maintain the platform at a desired location with respect to the template and the underwater installation; and bending stress reduction means provided at both the underside of the platform and the template for reducing local bending loads in the cable and the encapsulating tubing when the platform is moved laterally on the water surface with respect to the underwater template.

24. An encapsulated cable anchoring and tensioning v I 1 1 12 system as set forth in claim 23 wherein each of said bend References Cited ing stress reduction means comprises a guide trumpet UNITED STATES PATENTS which surrounds the encapsulating tubing where the tubing enters the platform and the template; each said 3142344 7/1964 Otteman et a1 "175 7 t th t d1 fl d th nd 3,327,780 6/1967 Knapp et al. 1140.5X lumps avmg an War y are PM 3 a 5 3,355,899 12/1967 Koonce et al. 61-465 gradually tapered wall leading to a concentric tubing section which closely surrounds the encapsulating tubing, 1472032 10/1969 Howard 61 46 the trumpets being arranged such that their flared mouths A face each other, whereby a substantially constant stress I COB SHAPIRO Primary Exammer level is provided at all vertical sections on the tubing 10 U S C1 X R,

which are under bending stress. 114 ,5, 179; 175 7