US3633369A

US3633369A - Method and apparatus for transporting and launching an offshore tower

Info

Publication number: US3633369A
Application number: US29994A
Authority: US
Inventors: Joseph Benton Lawrence
Original assignee: Brown and Root Inc
Current assignee: Brown and Root Inc
Priority date: 1970-04-20
Filing date: 1970-04-20
Publication date: 1972-01-11
Anticipated expiration: 1989-01-11

Abstract

A method and apparatus for transporting an offshore tower to a working site upon one or more articulated strings of freely pivotally connected flotation chambers. At a desired site, the flotation chambers are sequentially flooded to controllably lower the tower into the body of water. The flotation string may then be disconnected from the tower and controllably sequentially refloated for subsequent reuse.

Description

United States Patent Inventor Joseph Benton Lawrence Houston, Tex.

Appl. No. 29,994

Filed Apr. 20, 1970 Patented Jan. 11, 1972 Assignee Brown & Root, Inc.

Houston, Tex.

METHOD AND APPARATUS FOR TRANSPORTING AND LAUNCHING AN OFFSHORE TOWER 14 Claims, 14 Drawing Figs.

U.S. Cl til/46.5, 61/723, 114/.5, 114/435 Int. Cl E02b 17/02 E02c 5/00 Field of Search 61/465, 46,

81, 82, 72.3, 52; l 14/.5 D, .5 F,43.5, 52

[56] References Cited UNITED STATES PATENTS 3,472,035 10/1969 Broussard et al. 6l/72.3 3,507,126 4/1970 Rochelle et al. 61/7213 3,036,438 5/1962 Sims 6l/46.5 X FOREIGN PATENTS 625,728 l96l Italy 61/723 Primary Examiner-Jacob Shapiro Attorney-Burns, Donne, Benedict, Swecker & Mathis ABSTRACT: A method and apparatus for transporting an offshore tower to a working site upon one or more articulated strings of freely pivotally connected flotation chambers. At a desired site, the flotation chambers are sequentially flooded to controllably lower the tower into the body of water. The flotation string may then be disconnected from the tower and controllably sequentially refloated for subsequent reuse.

PATENTEnJm 1 m2 3.633369 SHEETlUFS FIGZ JOSEPH BENTON LAWRENCE EMA/4100M. 9W

ATTORNEYS PATENTED JAN: 1 m2 SHEET 2 OF 5 PATENTEU mu 1 me I SHEET 3 or 5 Q i A. w w m p Q 1 \m I l I I! III A. W g g f 1 K E of 27W i 8 M W E u T n 11111 m: N -m H w: m w n m 3 EM NN :5 A K w: N f u. zz: 552 55 8 w: w llllll l|v.|lII 6: Ti l mimmm 1m 3 633 369 SHEEI a UF 5 slrsaalsss PATENTED JANI 1 I972 SHEET 5 [IF 5 METHOD AND APPARATUS FOR TRANSPORTING AND LAUNCI-IING AN OFFSHORE TOWER BACKGROUND OF THE INVENTION This invention relates to a method and apparatus for transporting and erecting an offshore tower at a desired working site within a body of water such as for example a lake, sea or ocean.

More particularly, the invention relates to an improved launching vessel and launching process for safely and efficiently positioning a large ofishore tower upon the bed of a body of water. Towers have a multiplicity of applications in a marine environment, such as for example supports for radar or sonar stations, light beacons, scientific marine exploration labs and the like. Additionally, offshore towers are frequently used in the oil industry in connection with drilling, producing and distributing operations.

Drilling for oil in oil or gas fields situated beneath the surface of a body of water has in the recent past become an extremely active and important segment of creativity in the oil industry. While in the initial stages of development, exploration and drilling were conducted in locations of relatively shallow water depths from a few feet to 100 or 200 feet, such as exists along the near shore portions of the Gulf of Mexico, it has more recently been the accepted practice to establish sites in water depths from a few hundred to 1,000 or more feet, such as exists along the Pacific coast continental shelf and in the Arctic regions.

In order to exploit mineral resources which exist below such a substantial depth of water, tower designs which have been reliable and effectively utilized in the past have undergone redesign for prolonged high stress, deep water use. In this connection offshore towers are enormous structures presenting truly significant engineering challenges not only from an initial design aspect but from a subsequent construction, transportation and erection point of view.

At least one previously known method of transporting and launching a relatively shallow water tower comprises transporting a tower to a desired working site, resting upon a pair of pivotally connected barges.

One barge is considerably larger than the second and when ballasted will serve as a support in a jackknifing erection operation. In this connection hydraulic cylinders are coupled between the two barges to pivot the smaller barge and the tower into an approximately vertical posture.

While such an apparatus and technique may be satisfactory for shallow water and towers of relatively small size, it has been found that this process is infeasible for most deep water applications.

Another method of transporting and erecting an offshore tower which has been effectively utilized in deep water locations comprises segmenting the tower legs with bulkheads into ballast compartments and floating the tower to an offshore site on the buoyant tower legs. At the work site the compartments are flooded to sink the tower to the bed of the body of water.

While this technique is frequently adequate, it has recently been desirable to drill through the tower legs. It will be readily realized that flotation compartment bulkheads obstruct the free placement of conductors within the legs at an offshore site and/or require intricate shipyard fabrication.

Further a lack of universal application or reuse often makes such a concept of transportation and erection economically undesirable.

A further known method of transporting and launching offshore towers comprises attaching one or more pontoons to the exterior of the tower structure and floating the tower to a working site resting upon the pontoons, then releasing the pontoons to enable the tower to settle upon the bed of the body of water. However, floats or pontoons attached to a drilling tower are under enormous loads. Releasing the pontoons from the weight of the tower immediately unleashes buoyancy forces corresponding to the previous weight of the supported tower with the resultant effect of an almost explosive throwing and thrashing of the flotation chambers. This violent action in conjunction with the enormous pontoon sizes required to support current deep water offshore towers renders the operation extremely hazardous to personnel and equipment.

It would therefore be desirable to provide a safe and efficient method and apparatus for transporting offshore towers of large dimensions to a suitable working site and controllably lowering the tower within the body of water. Additionally, it would be advantageous to be able to safely detach the apparatus from the tower so as not to interfere with drilling operations and permit reuse in subsequent transport and erection operations. Further, it would be desirable to provide a method and apparatus which would be universally applicable to a variety of tower designs and therefore economically attractive.

OBJECTS AND SUMMARY OF THE INVENTION It is therefore a general object of the invention to provide a method and apparatus to obviate or minimize problems of the type previously described.

It is a particular object of the invention to provide a method and apparatus for controllably transporting and launching a deep water offshore tower within a body of water.

It is a further object of the invention to provide a method and apparatus for transporting and launching an offshore tower whereby the apparatus may be removed from the launched tower for reuse in subsequent operations.

It is a still further object of the invention to provide a method and apparatus for launching an offshore tower which will minimize the hazards to equipment and personnel during the launching operation.

It is another object of the invention to provide an apparatus for transporting and erecting an offshore tower which may be self-contained and remotely controlled.

It is still another object of the invention to provide a method and apparatus for transporting and erecting an offshore tower which will minimize the stress and load requirements placed upon the apparatus to thus minimize the possibility of failure while simultaneously minimizing the structural design requirements.

It is yet another object of the invention to provide a method and apparatus for transporting and launching an offshore tower which is universal in application and may be readily adapted to accommodate a plurality of tower designs and configurations.

It is yet a further object of the invention to provide a method and apparatus for transporting and launching an offshore tower which will not hinder subsequent drilling operations and will be economically attractive.

THE DRAWINGS Other objects and advantages of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings, wherein:

FIG. I is an isometric view of an offshore tower positioned within a body of water, having attached along a lateral surface apparatus for transporting and launching a deep water offshore tower according to one preferred embodiment of the invention, including two articulated strings of flotation vessels freely pivotally connected at their ends;

FIG. 2 is a side elevational view of one of the flotation vessels, which has been partially broken away to disclose the interior thereof, according to one preferred embodiment of the invention;

FIG. 3 is a side elevational view of FIG. 2 disclosing one of the flotation vessels partially broken away to disclose the interior thereof and further illustrating clamps used to connect each of the flotation vessels to a lateral surface of an offshore tower;

FIG. 4 is a detailed view of a clamping arrangement according to one embodiment of the invention;

FIG. 5 is a detailed view of a second clamping arrangement according to another embodiment of the invention;

FIG. 6 is a schematic view of a portion of the control mechanism utilized with a flotation vessel as illustrated in FIGS. 2 and 3;

FIG. 7 is another schematicview of a control arrangement according to one embodiment of the invention; and

FIG. 8-14 disclose in a schematic array a preferred method of transporting and erecting an offshore tower utilizing the articulated string of flotation chambers according to the invention.

DETAILED DESCRIPTION Referring now to the drawings, and more particularly to FIG. 1 thereof, there will be seen an offshore tower resting upon the bed 22 of a body of water 24 and extending above the surface 26. The tower includes generally vertically legs 28 which extend from the bed to above the surface of the body of water. The legs are interconnected at select locations along the length thereof by horizontal braces 30 and sloping struts 32 which adds stability thereto. Positioned at the lower end of the tower is a sloping skirt arrangement 34 resting upon the bed of the body of water to provide a widespread sable base for enhancing the lateral stability of the tower design. The specific tower structure 20 per se does not form a part of this invention, but merely represents one of a multiplicity of currently utilized tower designs. Rather, releasably connected along the vertical legs 28 are articulated strings of buoyancy vessels 36 pivotally connected at their ends in tandem which serve to transport the tower 20 to a preselected offshore site and erect the same in a controllable manner in accordance with a preferred embodiment of the invention.

The articulated strings 36 may be interconnected in a mutually parallel posture by generally horizontal braces 42 and crossing struts 44. The axes of the strings 36 are held in a generally parallel posture with respect to the central axis of the offshore tower 20.

The articulated strings 36 are composed of individual buoyancy vessels 33 pivotally connected at their ends by hinge plate arrangements 40. The hinge plate arrangements 40 permit the individual chambers to mutually freely pivot for reasons which will become apparent hereinafter. The braces 42 and struts 44 as previously mentioned maintain the generally parallel posture between adjacent individual flotation chambers 38 making up the articulated string 36 and serve to prevent lateral twisting displacement about the tower legs 28.

Turning now to FIGS. 2 and 3, there will be seen detailed views, partially broken away, of an individual flotation vessel 38. The vessel 38 is fabricated with a generally cylindrical skin 46 which is closed at its ends by hemispherical caps 48 to form a watertight chamber. A vent valve 50 is tapped into the upper end of the vessel and serves, in the open posture, to permit the rapid ingress of ballasting fluid into the flotation vessel 38.

Each flotation vessel 38 is provided with a fore hinge plate 54 and an aft hinge plate 56. The hinge plate 54 is provided with a plurality of cylindrical fingers 58 which serve to mate with compatibly spaced fingers 60 in the aft hinge plate 56 of a corresponding flotation vessel 38. A pin may be intimately received through the mating fingers to pivotally bind the flotation vessels in a freely pivotally connected articulated string. The

hinge plates

54 and 56 are fixedly mounted to the flotation vessel 38 by suitable tying brackets 59 having coped end surfaces 61 for intimate engagement with the spherical end portions 48 of the, flotation vessel. The coped end surfaces 61 may be fixedly welded to the end spheres 48 to integrally attach the

hinge plates

54 and 56 to the outer skin of the flotation vessels 38.

In those instances where a pair of articulated flotation vessel strings 36 are affixed to an offshore tower for the transportation and erection thereof the strings are fixedly interconnected in a generally parallel posture by a plurality of generally horizontal braces 42. Further, crossing struts 44 are utilized to insure the generally parallel configuration of the flotation chambers under excessive loading conditions. While it will be recognized that a single string of vessels 36 may be adequate for many applications, in those instances where the possibility of twisting of the strings 36 about the tower periphery exists, a pair of interconnected strings is preferred.

Each of the flotation vessels 38 is independently clamped to a vertical leg 28 of the ofi'shore tower by one or more pivotal C-clamp arrangements 62, as best seen in FIGS. 3, 4 and 5. A pair of bridging brackets 64 extend normally from the generally cylindrical skin 46 of the vessel in an upper and lower position. Pivotally connected by pin junctions 68 at the free end of each bracket 64 are a pair of generally C-shaped embracing arms 66. The arms 66 are so dimensioned as to intimately embrace a tower leg 28 and releasably attach the vessel 38 thereto.

Referring now specifically to FIG. 4, there will be seen one embodiment of an actuation system which serves to control arms 66. More specifically, a pair of hydraulic cylinders 70 may be pivotally connected at one end to the bracket 64 as at 72. The cylinders 70 are provided with axially reciprocating rams 74 which pivotally connect at their free ends to lateral portions of the arms 66 as at 76. Fluid from

control lines

78 and 80 serves to reciprocate the rams 74 within the cylinders and thus control the clamping movement of the arms 66.

An alternative embodiment for clamping flotation vessel 38 to an offshore tower is specifically illustrated by FIG. 5. More specifically, the generally C-shaped arms 66 are provided at their outer ends with tab extensions 82 having one or more apertures therein. Conventional explosive fasteners 84, such as for example explosive bolts, are positioned through the apertures to maintain the secure embracing relationship of the arms 66 with a tower leg 28 until the fasteners 84 are detonated.

Each flotation vessel 38 is provided in one preferred embodiment with an internal compressed gas cylinder 86, which is fixedly positioned relative to the cylindrical skin 46 by radially extending spoke brackets 88.

The buoyancy of each flotation vessel 38 may be independently controllable from a remote source by a system utilizing the internal compression cylinder 86 in a manner schematically illustrated in FIG. 6. The compressed gas cylinder 86 is preferably provided at its upper end with a blow valve comprising, for example, a direct acting four-way spool valve 90. The valve 90 is normally biased by a spring 92 in a left-hand mode, as viewed in FIG. 6, wherein the compressed gas cylinder 86 is in normal communication with a plug 94. The plug maintains the scaled integrity of the cylinder 86 but permits rapid refilling of the gas cylinder at desired intervals. To accomplish this refilling operation a port (not shown) must of course be fashioned through the vessel skin. This port may be easily rescaled, however, so that the vessel may be reused in a flotation capacity. A remotely controlled electromechanical mechanism, such as for example a solenoid, may be selectively actuated which will serve to shift the spool valve 90 to a righthand posture, as shown in phantom. In this position the valve 90 will connect the interior of the compressed gas cylinder to a check valve 98 and therethrough to the interior of the flotation vessel 38.

A ballast fill or jettisoning discharge valve 52 is positioned, as previously mentioned, in the lower hemispherical shell 48 of the flotation chamber 38. The valve 52 comprises a direct acting normally closed two-way sleeve valve being biased in a normally closed mode by a spring 100. An electromechanical mechanism 102, such as for example a solenoid, may serve to actuate the valve 52 to a left-hand posture, as viewed in FIG. 6. In this mode the interior of the flotation tank will be directly connected with the ambient sea water environment and the vessel 38 will take water.

Integrally connected into the upper hemispherical shell 48 is a vent valve 50 comprising a direct acting normally closed two-way valve, similarv to the previously discussed ballast fill or jettisoning discharge valve 52. Like valve 52 the vent valve is provide with a spring bias 104 to normally maintain the valve in a closed posture or left-hand mode, as viewed in FIG. 6. An electromechanical device 106, such as for example a solenoid, serves to shift the valve to a right-hand posture shown in phantom and connect the interior of the flotation vessel 38 through a check valve 108 to the ambient environment.

The

electromechanical mechanisms

96, 102 and 106 may be electrically operated by connections, not shown, to a surface vessel or may each may be provided with coded sonar responsive actuating mechanisms as desired. In any event each of the valves 50, S2 and 90 are designed to be independently and selectively actuated from a remote location such as a control barge floating upon the surface of the body of water 24.

Referring now to FIG. 7 there will be seen an alternative control system for regulating the buoyancy of the articulated string of flotation vessels 36. More particularly, a supply of fluid, such as air under constant pressure, is schematically represented by closure 110. It will be understood that this supply may be mounted upon a control barge (not shown) with an umbilical cord composed of a plurality of lines running to each flotation tank 38. The supply system 110 may comprise a motor driven compressor system or may be merely a large tank of compressed air mounted upon the vessel.

An air supply line 112 leads from the supply system 110 and is separated by an open cross into a control line 114, a power line 116 and a clamp actuation line 118.

The power line 116 runs to a manually controllable direct acting two-way blow valve 120 and through a check valve 122 to the interior of the flotation vessel 38. The blow valve 120 is mounted adjacent a control panel positioned aboard the control vessel. The power line 116 downstream of the check valve 122 branches into a remotely controllable direct acting normally closed two-way vent valve 124 which may be mechanically operated by a spring biased piston and cylinder 126. The valve 124 in the open position connects the control line 116 downstream of the check valve and thus establishes communication between the interior of the vessel 38 and the ambient environment.

The lower hemisphere 48 of the flotation vessel 38 is tapped by a conduit which leads directly into a direct action normally closed two-way valve 128. Valve 128 may be controlled by a piston and cylinder 130. The piston and cylinder 130 is spring biased such that the valve is normally in a closed posture. In the open position, valve 128 leads directly into the ambient environment and thus may be accurately termed a ballast fill or jettisoning discharge valve.

The vent valve 124 and ballast fill or jettisoning discharge valve 128 are physically connected to the flotation vessel 38 and are remotely controlled by direct acting normally closed two-

way valves

132 and 134, respectively. These valves are manually operable by a toggle switch and are connected adjacent the control panel mounted aboard the support vessel. The

valves

132 and 134 are further directly connected with the control line 114 for selectively and controllably supplying air pressure to the

valve actuating mechanisms

126 and 130.

The clamp actuation line 118 connects directly into a direct acting two-way valve 132 which is mounted adjacent the control panel and may be manually operable by a toggle switch. The control valve 132 leads directly into one of the two

control lines

78 or 80 which connect directly with the vessel mounted cylinders 70. As previously discussed these cylinders in conjunction with rams 74 to actuate the clamping arms 66 to releasably embrace and clamp the flotation vessels 38 to the legs 28 of an offshore tower 20.

While the above discussion referred to a single vessel 38 and its control valves, additional control circuits may be fed from a branch line 136 to supply pressure for control valves as needed tor additional vessels and an additional power and clamp actuation line 138 extends to serve a similar number of additional vessels in a manner as previously discussed in connection with the single vessel 38 illustrated in FIG. 7.

While FIG. 1 discloses strings 36 of five flotation vessels 38 the number is merely representative and it will be appreciated that in actual operation more or less may be utilized. Further, each vessel 38 is'substantially identical and thus individual vessels may be readily added or removed to accommodate a variety of offshore tower designs. Further, if one or more vessels 38 should become damaged or excessively worn, that vessel may be readily replaced without replacing the entire string of vessels.

The sequencing and mode of operation of each of the above-described elements will be discussed more fully hereinafter in conjunction with the overall mode of operation of the flotation and launch vessel.

METHOD OF TRANSPORT, LAUNCHING AND RECOVERY Referring now specifically to FIGS. 8-14, there will be seen in a schematic array, a generally sequential depiction of transporting an offshore tower to a selected site, controllably erecting the tower upon the bed of the body of water and retrieving the transport and launch apparatus.

More particularly and referring to FIG. 8 there will be seen an offshore tower 20 horizontally supported along the surface 26 of a body of water 24 by at least one articulated string of buoyancy chambers 36 pivotally connected at their ends in tandem. The tower in its horizontally floated posture may be towed to a desirable offshore site by a control barge 140. In the transportation posture, each of the individual flotation vessels 38 is substantially void of water and the vent, blowing and ballast fill or discharge valves are all in a closed posture.

Upon reaching a desired site, as illustrated in FIG. 9, the individual flotation chambers 38 are sequentially ballasted beginning with the lowermost vessel 144 and progressing toward the uppermost chamber 146 in sequential order to induce an upending of the tower 20 into the body of water 24. In order to induce the entry of ballast or water into the chamber 38, the ballast valve is opened along with a vent valve while the blow valve is maintained in a closed posture. It will readily be realized that the vent valve permits water to freely enter through the ballast valve without simultaneously displacing air through this valve thus insuring a more easily controllable ballast operation.

The individual vessels 38 are designed so that upon being freely filled with water they are approximately neutrally buoyant. In this connection it may be necessary to establish one or more air chambers (not shown) within the interior of each vessel 38 or a compressed gas cylinder 86 attached to each of the vessels may be so dimensioned to provide the desired neutral buoyancy upon full flooding.

During the erecting operation the vent and ballast fill or discharge valves are held in an open posture to permit the free ingress and egress of water such that differential pressures between the interior and the exterior of each flotation vessel 38 is maintained approximately zero with any depth of water. This permits the skin of the vessel 38 to be fabricated with less thickness than would be possible if a substantial pressure differential were allowed to build up particularly with respect to the bottom vessel 144.

Referring now to FIG. 10, the individual flotation vessels have been ballasted or flooded to neutral buoyancy, and the offshore tower 20 being positively buoyant is free to bob in a generally vertical posture within the body of water 24.

After the offshore tower 20 is thus righted, the articulated string of flotation vessels 36, as best seen in FIG. 11, are simultaneously released from the offshore tower by the separation of the clamp arm 66 all along the lateral surface of the offshore tower. As previously discussed, the release operation may be produced by a variety of mechanisms and modes of operation. However, two methods which have been found to be satisfactory are explosive bolts 84 or hydraulic rams 74. Due to the neutral buoyancy of the individual flotation chambers 38 during this separation operation, there will be a minimum tendency to produce high shear forces in the C- clamp couplings 62 and along the lateral legs 28 of the offshore tower. The thus released articulated string of buoyancy vessels 36 freely hang in a vertical posture within the body of water 24 along the lateral surface of the tower.

In order to controllably recover the string 36 for future use, the individual buoyancy vessels 38 are sequentially blown beginning with the uppermost vessel M6 progressing toward the bottom vessel M4. During the blowing operation, the vent valve is closed, the blowing valve is opened and the ballast discharge valve remains open. After the individual chambers 38 are blown of their fluid and reach the surface, the ballast discharge valve and blowing valve may be closed.

Simultaneously, as best seen in FIGS. iii-l3, as the blowing operation proceeds, the control barge M connected to the uppermost vessel 146 is navigated away from the tower 20. This initially tips the uppermost vessel M6 away from damaging contact with the tower .20 while the remaining vessels 38 hang in a generally vertical posture also away from the tower.

As the individual chambers 38 are blown and reach the surface, they each pivot about their hinge connection 40 while the remaining lower ballast vessels hang generally vertical in the water. The movement of the control barge 40 away from the tower location and the sequential blowing of the individual vessels 38 insure a smooth resurfacing of the flotation vessels as the articulated string of buoyancy vessels 36 is towed away from the erection site.

Referring to FIG. 14, following the recovery of the articulated string of flotation vessels 36 the tower legs 28 may be flooded to set the offshore tower upon the bed 22 of the body of water 24. The tower may be then pinned to the subsea bed 22 by piles.

The tower thus erected may serve to stably support a platform M2 above the surface of the body of water for a multiplicity of uses as previously discussed.

SUMMARY OF SIGNIFICANT ADVANTAGES Thus it will be seen that the present invention provides an improved method and apparatus for transporting and launching a deep water offshore tower.

Particularly significant is the provision of a plurality of freely pivotally connected flotation chambers of uniform dimensions which may readily be replaced if one becomes worn or damaged and which further admits to assembling of as many chambers as is necessary to accommodate varying structural dimensions of offshore towers.

Another important feature of the invention is the self-contained nature of one preferred embodiment which minimizes the requirement for excessive support equipment and which may be remotely controlled.

Another advantage of the invention is the provision of parallel strings of flotation chambers which prevent corkscrewing or rotating of the vessel strings about the tower during the transport or launch operations.

Another significant advantage of the invention is the provision of controllably launching the tower and rapidly and controllably retrieving the transport and launch apparatus once the tower is in an erect position which minimizes hazards to personnel and equipment in the immediate working vicinity and which further frees the apparatus for subsequent operations.

A significant method aspect of the operation includes the provision of flooding to meet neutral buoyancy conditions of the flotation chambers and the simultaneous release of all of the chambers from the tower structure, thus minimizing or eliminating shearing stresses which would be created if the chambers were not neutrally buoyant or were released from the tower in a nonuniform manner. Further, the sequential flooding of the flotation chambers provides a high degree of control which minimizes the tendency of the tower to thrash about in the water. In addition, the maintenance of the ballast fill or jettisoning discharge valve in an open posture during the raising and lowering of the flotation vessels insures that an excessive pressure differential will not build up across the vessel skin.

Another significant advantage of the invention is the provision of the freely coupled articulated flotation chambers which may be sequentially blown, beginning with the chamber nearest the surface, and thus may be orderly removed from the immediate vicinity of the previously righted tower while the chambers remaining submerged will tend to hang in a vertical posture, thus minimizing the possibility of underwater bumping and potential damage to the tower.

Although the invention has been described with reference to preferred embodiments, it will be appreciated by those skilled in the art that additions, modifications, substitutions, deletions and other changes not specifically described may be made which will fall within the purview of the appended claims.

What is claimed is:

H. An offshore tower transport and launching apparatus comprising:

a first plurality of generally hollow elongate flotation vessels, each vessel having a longitudinal axis and said vessels being pivotally connected in substantially axial alignment for connection to the lateral surface of an offshore tower whereby the longitudinal axis of the offshore tower is substantially parallel to the aligned axes of the elongate flotation vessels;

a second plurality of generally hollow elongate flotation vessels, each vessel having a longitudinal axis and said vessels being pivotally connected in substantially axial alignment for connection to the lateral surface of an offshore tower whereby the longitudinal axis of the offshore tower is substantially parallel to the aligned axes of the elongate flotation vessels;

means for fixedly interconnecting corresponding vessels of said first plurality of flotation vessels with said second plurality of flotation vessels in a generally parallel posture;

means for releasably connecting said first and second plurality of flotation vessels to the lateral surface of the offshore tower;

means for selectively admitting fluid into each of said flotation vessels to submerge said vessels and the offshore tower within the body of water;

means for simultaneously disconnecting in a submerged posture each of said flotation vessels from the lateral surface of the offshore tower; and

means for selectively jettisoning fluid from the interior of each of said flotation vessels to induce the ascent of said vessels from a submerged posture in the body of water.

2. An offshore tower transport and launching apparatus as defined in claim 1 and further comprising:

means connected to each of said flotation vessels for establishing a generally neutrally buoyant state of each of said flotation vessels upon said vessels being flooded.

3. An offshore tower transport and launching apparatus comprising:

a plurality of generally uniform submergible flotation vessels pivotally connected in tandem for transporting on a body of water an offshore tower to a desirable offshore work site and for submerging with the offshore tower at the work site to position the offshore tower in an erect posture within the body of water;

means for admitting fluid into each of said flotation vessels to submerge said flotation tanks within the body of water;

means for releasably disconnecting in a submerged posture each of said flotation vessels from the lateral surface of the offshore tower; and

at least one chamber of compressed gasfixedly connected to each of said generally uniform flotation vesselsand having a selectively operable control means connecting the interior of said flotation vessel and said at least one compressed gas chamber for controllably jettisoning fluid from said flotation vessel.

4. An offshore tower transport and launching apparatus as defined in claim 3 wherein:

said at least one chamber of compressed gas is positioned within the interior of said uniform flotation vessel.

5. An offshore tower transport and launching apparatus as defined in claim 3 wherein:

said at least one chamber of compressed gas connected to said generally uniform flotation vessel is dimensioned to provide neutral buoyancy of said flotation vessel when said flotation vessel is flooded. 6. An offshore tower transport and launching apparatus comprising:

an articulated string of freely pivotally connected flotation vessels adapted to ferry an offshore tower to a drilling site; means for releasably connecting each of said flotation vessels to a lateral surface of the offshore tower; means for selectively flooding each of said flotation vessels thus permitting said offshore tower to sink into the body of water; and a high pressure chamber positioned within the interior of each of said flotation vessels and having at least one selectively controlled aperture therein for providing communication from within the pressure chamber to the region between said pressure chamber and :he shell of said flotation vessel. 7. An offshore tower transport and launching apparatus as defined in claim 6 and further comprising:

at least another articulated string of freely pivotally connected flotation vessels as defined in claim 6 and fixedly connected in a generally parallel posture with respect thereto. 8. A method of transporting and erecting an offshore tower comprising the steps of:

floating the offshore tower to an offshore site upon at least one articulated string of pivotally connected flotation vessels connected along a lateral surface thereof; sequentially flooding each of said flotation vessels beginning with the vessel attached nearest to the bottom of the offshore tower to permit said offshore tower to descend within the body of water; disconnecting said flotation vessels from the submerged offshore tower; and sequentially blowing said flotation vessels beginning with the vessel nearest the surface of the body of water to induce said flotation vessels to rise to the surface. 9. A method of transporting and erecting an offshore tower as defined in claim 8 wherein:

said flotation vessels are simultaneously disconnected from the submerged offshore tower. 10. A method of transporting and erecting an offshore tower as defined in claim 8 and further comprising the step of:

simultaneously with said step of sequential blowing towing said freely pivoted articulated string of flotation vessels away from the submerged tower. 11. A method of transporting and erecting an offshore tower as defined in claim 8 and further comprising the step of:

maintaining the flooding valve of each flotation vessel in the open position during the sequential flooding and blowing operations to minimize the pressure differential on the flotation vessels walls. 12. A method of transporting and erecting an offshore tower as defined in claim 8 wherein:

said step of sequentially flooding each of said flotation vessels proceeds only to the neutral buoyancy point of each of said flotation vessels. 13. A method of transporting and erecting an offshore tower comprising the steps of:

floating the offshore tower to an offshore site carried upon at least one articulated string of freely pivotally connected flotation vessels connected along a lateral surface thereof; sequentially flooding each of said flotation vessels to generally the point of neutral buoyancy beginning with the vessel attached nearest to the bottom of the ofi'shore tower to permit said offshore tower to descend within the body of water; disconnecting said flotation vessels simultaneously from the submer ed offshore tower; sequentla y blowing the said flotation vessels beginning

Claims

1. An offshore tower transport and launching apparatus comprising: a first plurality of generally hollow elongate flotation vessels, each vessel having a longitudinal axis and said vessels being pivotally connected in substantially axial alignment for connection to the lateral surface of an offshore tower whereby the longitudinal axis of the offshore tower is substantially parallel to the aligned axes of the elongate flotation vessels; a second plurality of generally hollow elongate flotation vessels, each vessel having a longitudinal axis and said vessels being pivotally connected in substantially axial alignment for connection to the lateral surface of an offshore tower whereby the longitudinal axis of the offshore tower is substantially parallel to the aligned axes of the elongate flotation vessels; means for fixedly interconnecting corresponding vessels of said first plurality of flotation vessels with said second plurality of flotation vessels in a generally parallel posture; means for releasably connecting said first and second plurality of flotation vessels to the lateral surface of the offshore tower; means for selectively admitting fluid into each of said flotation vessels to submerge said vessels and the offshore tower within the body of water; means for simultaneously disconnecting in a submerged posture each of said flotation vessels from the lateral surface of the offshore tower; and means for selectively jettisoning fluid from the interior of each of said flotation vessels to induce the ascent of said vessels from a submerged posture in the body of water.

2. An offshore tower transport and launching apparatus as defined in claim 1 and further comprising: means connected to each of said flotation vessels for establishing a generally neutrally buoyant state of each of said flotation vessels upon said vessels being flooded.

3. An offshore tower transport and launching apparatus comprising: a plurality of generally uniform submergible flotation vessels pivotally connected in tandem for transporting on a body of water an offshore tower to a desirable offshore work site and for submerging with the offshore tower at the work site to position the offshore tower in an erect posture within the body of water; means for admitting fluid into each of said flotation vessels to submerge said flotation tanks within the body of water; means for releasably disconnecting in a submerged posture each of said flotation vessels from the lateral surface of the offshore tower; and at least one chamber of compressed gas fixedly connected to each of said generally uniform flotation vessels and having a selectively operable control means connecting the interior of said flotation vessel and said at least one compressed gas chamber for controllably jettisoning fluid from said flotation vessel.

4. An offshore tower transport and launching apparatus as defined in claim 3 wherein: said at least one chamber of compressed gas is positioned within the interior of said uniform flotation vessel.

5. An offshore tower transport and launching apparatus as defined in claim 3 wherein: said at least one chamber of compressed gas connected to said generally uniform flotation vessel is dimensioned to provide neutral buoyancy of said flotation vessel when said flotation vessel is flooded.

6. An offshore tower transport and launching apparatus comprising: an articulated string of freely pivotally connected flotation vessels adapted to ferry an offshore tower to a drilling site; means for releasably connecting each of said flotation vessels to a lateral surface of the offshore tower; means for selectively flooding each of said flotation vessels thus permitting said offshore tower to sink into the body of water; and a high pressure chamber positioned within the interior of each of said flotation vessels and having at least one selectively controlled aperture therein for providing communication from within the pressure chamber to the region between said pressure chamber and the shell of said flotation vessel.

7. An offshore tower transport and launching apparatus as defined in claim 6 and further comprising: at least another articulated string of freely pivotally connected flotation vessels as defined in claim 6 and fixedly connected in a generally parallel posture with respect thereto.

8. A method of transporting and erecting an offshore tower comprising the steps of: floating the offshore tower to an offshore site upon at least one articulated string of pivotally connected flotation vessels connected along a lateral surface thereof; sequentially flooding each of said flotation vessels beginning with the vessel attached nearest to the bottom of the offshore tower to permit said offshore tower to descend within the body of water; disconnecting said flotation vessels from the submerged offshore tower; and sequentially blowing said flotation vessels beginning with the vessel nearest the surface of the body of water to induce said flotation vessels to rise to the surface.

9. A method of transporting and erecting an offshore tower as defined in claim 8 wherein: said flotation vessels are simultaneously disconnected from the submerged offshore tower.

10. A method of transporting and erecting an offshore tower as defined in claim 8 and further comprising the step of: simultaneously with said step of sequential blowing towing said freely pivoted articulated string of flotation vessels away from the submerged tower.

11. A method of transporting and erecting an ofFshore tower as defined in claim 8 and further comprising the step of: maintaining the flooding valve of each flotation vessel in the open position during the sequential flooding and blowing operations to minimize the pressure differential on the flotation vessels walls.

12. A method of transporting and erecting an offshore tower as defined in claim 8 wherein: said step of sequentially flooding each of said flotation vessels proceeds only to the neutral buoyancy point of each of said flotation vessels.

13. A method of transporting and erecting an offshore tower comprising the steps of: floating the offshore tower to an offshore site carried upon at least one articulated string of freely pivotally connected flotation vessels connected along a lateral surface thereof; sequentially flooding each of said flotation vessels to generally the point of neutral buoyancy beginning with the vessel attached nearest to the bottom of the offshore tower to permit said offshore tower to descend within the body of water; disconnecting said flotation vessels simultaneously from the submerged offshore tower; sequentially blowing the said flotation vessels beginning with the vessel nearest the surface of the body of water to induce said string of flotation vessels to rise to the surface; and simultaneously towing said at least one articulated string of freely pivotally connected flotation vessels away from the submerged tower.

14. A method of transporting and erecting an offshore tower as defined in claim 13 and further comprising the step of: maintaining the flooding valve of each flotation vessel in the open position during the sequential flooding and blowing operations to minimize the pressure differential on the flotation vessels walls.