GB2481906A

GB2481906A - A template structure for erecting underwater columns

Info

Publication number: GB2481906A
Application number: GB1111425.3A
Authority: GB
Inventors: Peter Leonard Fraenkel
Original assignee: Marine Current Turbines Ltd
Current assignee: Marine Current Turbines Ltd
Priority date: 2010-07-05
Filing date: 2011-07-05
Publication date: 2012-01-11
Also published as: GB201011251D0; GB201111425D0; JP5813109B2; JP2013529736A; EP2591175A1; CN103119222A; KR20130049804A; WO2012004556A1

Abstract

A temporary template structure for placing columns or piles underwater. The structure includes an elongate leg member 1 which extends perpendicularly from a base 3 to a platform 5 which it supports. The structure may be carried to a suitable location by catamaran and may be launched from in between the two hulls of a catamaran. The structure may include a drill unit 7, a grouting system, a crane 8, ballast 4 and strakes 9.

Description

SURFACE-BREAKING REUSABLE SUBMERGEABLE TEMPLATE

FOR 1NSTALUNG ONE OR MORE SUBMERGED COLUMNSIPILES

BACKGROUND TO THE INVENTION

This invenflon relates to improving the ease of installation of columnar members such as pile-type foundations in a sea, river or lake bed, (or any other location where a liquid of significant depth flows over a hard ground surface) and in particular (but not necessarily) in locations with strong currents.

The most reliable known method of founding structures such as those needed to carry bridges, jetties, off-shore wind-turbines or tidal turbines is to mount them on a pile (or a mono-pile) or on a pattern of piles (using a jacket structure to attach to the piles) that have been driven or drilled a suitable depth into the ground below the sea, river or other stretch of water, or for that matter any other liquid. In areas with strong currents this is particularly difficult because the bed tends to be eroded by the current to a rock or other hard surface requiring rotary' drilling which, in turn, generally requires a fixed and steady structure to support the drill unit and associated drill string during the drilling process. Moreover, in areas with strong currents the drill string needs to be protected from disruption by the current so it is common practice to drill through a fixed conductor tube extending substantially vertically from above the surface of the water to the point on the sea or river bed where drilling is to take place. It is, in practice, therefore only possible to drill from a floating vessel that is securely moored to anchor points capable of preventing significant movement of the vessel, which is difficult and costly to arrange in locations with strong currents and/or high tidal ranges. Vessels with dynamic positioning systems tend to be too costly and difficult to operate under such conditions and they and any other floating vessel will also heave in any significant wave state thereby making a drilling operation difficult to achieve.

Another option is subsea drilling piles into place through some kind of seabed or riverbed mounted template, but this is difficult to arrange as human intervention by divers or even using ROW (remotely operated vehicles) is virtually impossible in areas with strong currents. In practice, the power for drilling requires flexible umbilicals leading from a surface vessel to transmit both energy and control signals to the drill and this becomes extremely difficult to do in strong currents which can disrupt and flex the umbilicals, Hence, at present, the preferred method for installing piles at sea is to drill from a jack.up barge which can jack Usd1 up out of the water and stand on its legs on the sea bed using the weight of the jackedup hull to provide a stable fixed platform from where drilling can take place, usually from a hydraulic pile gate which can hold a suitable conductor tube in place.

However, there are numerous problems associated with the use of jackup barges since only those capable of rapidly jacking up and down can safely he used in tide races or other locations with strong currents, and in addition the feet oF the legs are often inappropriate for hard ground. Moreover, vortex shedding from the legs poses issues on stability as such shedding can cause dangerous resonant oscillations. Furthermore, jack-up barges capable of standing safely offshore with sufficient clearance for waves need to be relatively large and therefore they are expensive vessels and result in unacceptably high costs for many offshore or riverine applications.

Furthermore, the legs of a jack-up barge are always cantilevers because they need to be able to be raIsed and retracted through orifices In the barge hull, so It Is not possible to have cross-bracing or other strengthening measures below water. In additIon, It is dlfficuft to fit strakes or other means to inhibIt vortex shedding whereby the stability of a jack-up barge and depth ofwaterlnwNchftcanoperatewhenraisedonftslegsisllmftedbythe strength of the legs and in particular their resistance to buckling.

STATEMENTS OF THE iNVENTiON

According to one aspect of the present Invention, there Is provided a temporary template structure for the erection of one or more columnar members In a ground surface beneath of a column of lIquId, said template structure IncludIng an elongate leg member extending substantially perpendIcularly from a base structure, and said leg member serves to support a platform arranged substantially parallelly to said base structure..

According to a second aspect of the invention there is provided a method comprising transporting a temporary template structure to a desired location in a body of liquid, the template structure including a base structure, an elongate leg member extending substantially perpendicularly from said base structure and a platform arranged substantially parallelly to said base structure, sttmerng the base structure to be supported proximal to a ground surface beneath said body of liquid and arranging the platform to be supported substantially above an upper surface of the column of liquid distal from the ground surface.

According to a third aspect of the invention, there is provided in combination:- * a catamaran vesse' having first and second hus, and * a temporary template structure supported between the first and second hus and inc'uding an e'ongate eg member extending substantiaIy perpendicuarIy from a base structure, said base structure including a frame, and said eg member serves to support a p'atform arranged substantia'ly paralely to said base structure.

According to a fourth aspect of the invention, there is provided a template structure for p'acement at a desired bcation in a body of water inckiding a base structure for supporting an e'ongate tubu'ar eg member of sufficient iength to support a p'atform ocated substantiay above the surface eve of the body of water, wherein said platform serves to mount at east one driving unit, said dri unit comprising a driU string for dril'ing a co'umn-receiving ho'e in the ground surface be'ow the body of water upon which the temp'ate structure is supported.

According to a fifth aspect of the invention, there is provided a method of inserting one or more columns into a ground surface be'ow a body of water comprising supporting by an elongate tubular eg member a template structure upon the ground surface at a desired location, said template structure comprising a submerged base structure and a p'atform ocated substantia'ly above the surface eve of the body of water, activating a dri'l unit mounted on said p'atform via an associated dril' string so as to bore a co'umn-receiving ho'e in the ground surface, and introducing a co'umn into said ho'e through said e'ongate tubu'ar eg member.

Owing to these aspects, a template structure can be provided for facilitating safe and reliable installation of columnar members in the ground surface, even under adverse conditions such as where there is the likelihood of strong currents or waves.

Basically, the present invention provides a template structure which is designed to be temporarily self standing safely, even in strong currents or in water subject to a significant wave dilmate, wherein the template structure includes facilities to support the drilling of a hole or holes in the sea bed or riverbed, for the insertion of a pile or piles in preparation for a permanent structure to be subsequently installed on the site by attaching the permanent structure to the pre installed pile or piles and wherein the template structure when the pile or piles are in place, is readily movable and re-used for further such drilling operations.

Preferably, the transportation and handling the structure is by way of a specialised catamaran barge vessel.

Conveniently, the columnar members are in the form of piles which may be formed with the drill at the end thereof, and in such a case the pile can remain embedded in the drilled hole once sufficient penetration of the ground has been achieved by simply disconnecting the drill string, or else the drill together with the drill string maybe withdrawn through the vertical tubular elongate leg-like member or members and then a pile may be lowered into the hole through the vertical tubular elongate leg-like members using a crane or a winch.

Conveniently, the template structure may be used for other purposes than placing piles, for example for geo-technical survey drilling, as a temporary mooring for vessels, or for any other purposes where a stable platform can be bcated at the surface of the sea, river or other bed below a body of possibly fast moving water (or other liquid) may be usefully appiled.

Also convenienfly, the template structure can be such that the arrangement of the vertical tubular elongate legMke members (or a single member fri some oases) enables a standard pattern of piles (or a single pile) to be inserted in holes driiled into the ground below the sea or other ilquid and wherein the template structure may be ifted off the piles (or pile) after they (it) have been installed to leave them (it) ready for some useful structure (for example an offshore wind-k rbine, a channel marker, a bridge pier or a tidal turbine) to be lowered and affixed to them (or it) later.

Furthermore, after the pile(s) has/have been placed they can be subsequently grouted into the holes by providing a groutina system on the platform located above water or liquid level which can feed the grout through a hose or hoses deployed through the vertical tubular elongate leg-like member or members and into suitable grout channels within the pile or piles.

Conveniently, the template structure incorporates a relatively heavy base which can be ballasted with kentledge to make it heavy enough to stand safely even in locations with very strong currents.

Preferably, the structure is provided with leveling jacks between the footings and the main base structure such that after the template structure has been deposited on the ground or seabed it can be accurately leveled before the drilling process commences.

Conveniently, the leveling jacks may be hydraulic rams, screw lacks or any other mechanism capable of lifting a substantial weight.

In a preferred construcflon of the template structure, the vertical elongate legs may have vertical or spiral strakes or other flow "spoHers attached at their upstream and downstream stagnahon points in order to inhibit vortex shedding which would otherwise occur from cyUndrical members exposed to a fast flow of liqthd.

In an akernative arrangement, the flow spoflThg may be achieved by using non-cylindncal vertical elongate legs; for example with streamlined fairings.

elliptical or diamond shaped in profile which may in some oases not only inhibit vortex shedding but also be advantageous in reducing drag and hence the load on the structure.

Conveniently, cross-bracing members may be provided between the vertical tubular elongate leg members to increase the overall strength of the structure and its resistance to buckling of its legs, such cross bracing being preferably but not necessarily aligned to minimise drag; eg., rectangular section members should preferably be set so their longer dimension aligns with the direction of the flow of the current.

A preferred mode of transporting the template structure to a location of use utilises a conventional crane-barge or a specialised twinhulled vessel capable of lifting the structure between its hulls using either an on-board crane or cranes or onboard winches and used to convey the template structure to the desired site, to lower it into place, to raise it and to retrieve it after the drilling operations and the placing of piles has been completed.

Alternatively, the template structure is provided with buoyancy chambers or other floatation methods such as floatation bags to convey it afloat to the desired site under tow from a tug type of vessel and where such buoyancy aids can be flooded or progressively detached in order to enable the structure to sink when at the desired location.

After the drilling operations and the placing of thes has been completed the lloatatlon devices will then be pumped out or reattached In order to refloat the structure and retrieve It after the drilling operations and the placing of piles has been completed.

in a further construction of the template structure, a sleeve or sleeves can be positioned co-axially with and below the vertical tubular elongate leg member or members such that the sleeve or sleeves extends the leg-like member from Its base to the actual sea-bed or underwater ground level and thereby protects the drill string or grout hoses from the force of the passing current in what would otherwise be a gap.

Conveniently, the sleeve or sleeves may be lowered through the vertical tubular elongate leg member or members prior to drilling or may be retracted around the outside of the lowermost part of the leg member when not in use and lowered by releasing a suitable catch or fastening when the structure Is In -and standing on the seabed, riverbed or other ground with liquid above It.

Furthermore, the vertical tubular elongate leg member or members can have sections removed or inserted in otto vary their length and thereby perrnittheuseofthetemplatestructureinvaryingdepthsofwater(orother liquid).

Conveniently, the template structure has integrated features (for example hydrof oils) possbly integral with the cross bracing that make use of the flow of water to create a net downwards orientated lilt' force that assists gravity in holding the template structure onto the sea (or river) bed.

Preferably, when the template structure is positioned with its base just clear of the bed of a column of water I.e., sea bed or river bed, the tubular elongate leg members are of a height such that the platform is located above the surface of the water even If waves are present.

Conveniently, different units may be designed for different depths of water or alternatively detachable sections of the tubular elongate leg members may be removed or added to cater for different water depths.

As a convenient mode of installallon, a catamaran (twIn-hull) vessel wIth sufficient space between Its hulls to accommodate the template structure substantially above water level can be used to transport the structure to a required locaLlon at which point the structure can be lowered to the bed of the sea, river or any other expanse of water either by using an on-board aaneorbyuSngwinchesaswiUbeeiaboratedlater The tubular elongate leg members of the terrplate structure are arranged such that they can be positioned vertically upstanding when the base Is lowered to rest on footings on the sea bed (or rIver bed or any other such ground with water above it). The footings project below the base structure sufficiently far for the base structure to clear commonly found unevenness or loose rocks In the ground or bed and will generally be mounted on outriggers or extensions from the base or chassis of the template structure to give sufficient spacing for the stability of the structure, to ensure against toppling when there are strong currents, when standing on the bed of the sea, river or other water flooded space.

The footings will usually have poInted feet to give grip on hard surfaces, but other forms of feet may be fitted to suit different ground conditions. Each fooling is also equipped with extendab&retractable leveling devices such as hydraulic ram driven jacks or posstly electrically or hydraulically activated screw jacks or any other such device capable of adjusting the vertIcal heIght of each footing, so as to compensate for unevenness of the ground on which it stands within reasonable limits such that the titular memberscanbeadjustedsoastobetrulyverticalandsothattheplatform mounted to the tubular leg members Is then truly horizontal after the template structure footings have come to rest on the ground below the water or other lIquid.

Once correct vertical positioning has been achleved, an Internal sleeve may be lowered through the tubular elongate leg members to rest on the ground below and thereby extend the conductor tube from the base frame which Is clear of the ground. Furthermore, an alternative external sleeve may also be used for this same purpose which couki be released by remote control from below the vertical tube like leg member once the structure Is correctly positIoned. Once there Is an effete protected conductor tube between the top of the structure and ground or sea bed level has been achieved, then rock-drill drive rotary units or alternatively pile-driver type hammer units mounted on the top end of the tubular members above the platform can be used to power a drill string down through them and into the ground (or any other drilling technique such as water jetting maybe used).

Thedrllistilngmayhaveatftsiowermostend,apilefittedwithddulng cutters which can be drilled anWor hammered to the desired depth and then disconnected by an automatic release mechanism or alternatively, and more conventionally, removable drill stings are used to drill the holes and after these have been wkhdrawn the pile can be lowered down the same tubular member and into the ground using a crane or winch mounted on the top platform above water leveL The pile when bwered nb place can be pre*iitted with grout hoses and suitable internal grout pipes or channels such that grout may be pumped into the pile and it can be grouted into its hole after t has been lowered nto place. The grout hoses will be protected as they will be wfthin the tubular elongate leg members which effectively act as conductor tubes as weil as acflng as egs br supporting the above water platform. The grouting equipment may be carried on the top platform to deilver to the hoses.

The preferred embodiment of the template structure involves three footings, as these can be arranged to share the weight of the template structure regardless of the unevenness of the ground on which it stands. However, if required, more focUngs can be used to drill a multiple spread of piles and in that case the aforementioned jacks for leveling can be adjusted to share the load evenly as weD as to level the structure by sequentiafly pm-loading and set ing each looting until stability is achieved. With hydraulic systems, the loading may be determined from the hydraulic pressure.

The preferred embodiment uses three tubular elongate leg members which can be used as a template for drilling a spread of three piles suitably for a tripod4ype of jacket structure. However, the same kind of structure can be used to accommodate as ittle as a single support leg member, or three leg members with one of them of larger cross *sectiona diameter through which a mono pile can be drilled and installed, or more than three leg members to accommodate multiple footing jacket foundations.

Owing to the fact that the legs need not be raised through a hull, as with a jack-up barge, an advantage of this invention is that the template structure wili generaliy be cross-braced below water level considerably to enhance its strength and to permit much greater stability and resistance to vibration (e.g. from vortex shedding) than in the case of jack-up barges. The cross-bracing is preferably aligned so that it has a low drag prothe to the direction of flow of the currents.

Strakes for inhibiting vortex shedding may be fixed vertically to the leg members upstream and downstream of the direction of flow of the currents or arranged in a spiral around each leg member to inhibit the "wrap-around or Coanda effect, where cylindrical members shed vortices cyclicafly in flowing fluids, or aRernatively the leg members may be of non-circular cross-section, such possibilities include elliptical, other streamlined profile cross-sections or diamond shaped cross-sectional profiles to reduce drag and prevent vortex shedding.

The template structure needs to stand safely even when exposed to the fastest currents to be expected at the site, which will require it to be of sufficient weight to resist any tendency for the template structure to slide or topple due to the drag of the current, Therefore, the base frame or chassis has space for the addilion of ballast, sometimes known as kentledge to be clamped to it. Alternatively, to avoid the need for clamping, box like open-topped containers can be provided into which ballast may be deposited. In many cases the ballast will be steel or iron billets, old chain or other dense and heavy but low cost materials.

The ballast may be permanently in place or it may in some situations be added after the structure has been lowered into position. Extra ballast can if necessary be added to the platform above water level if necessary by craning it into position from an accompanying crane barge.

The aforementioned crossbracing may also optionay indude or carry horizontal hydrofolls positioned such that they wifl produce a down-force proportional to the square of the velocity of the current to help improve the stability of the structure and reduce the need for baflast'kentledge.

The platform above water level will also normally be used for carrying any other facilities needed for the operation, such as cranes, winches, generating equipment to provide power for drilling, grouting systems, accommodation for the crew, safety equipment, etc. Furthermore, space will normally be provided for the piles which can be stacked, for example, vertically to enable them to be easily hf ted and lowered (by an onboard crane or winch) into the support leg members when the holes have been drilled.

In practice, means are required to be able to transport the template structure to a required location of use and then subsequently to lift it and to transport it away from said location after the piles have been positioned.

Such transport possibilities include the use of a conventional crane barge, or a basic barge with a mobile crane installed on it, to carry it or to transfer it from another barge. Alternatively, flotation devices may be used to make the structure float, hence it could be towed to site using tug(s). In such cases it may be floated either vertically or more likely on its side from which position it would be rotated to a vertical position during the sinking sequence.

However, a preferred method is to use a dedicated catamaran (twin-hulled barge) of such construction that the spacing between the hufls is such that the template structure can be positioned verticafly between therm Sea-fastenings wifi be used when it is raised in order to secure the template structure to the catamaran barge for transit to the site.

A crane, or more preferably deck-mounted winches, wifi hold the template structure in position when the barge is positioned on site and the sea-fastenings are released, and then by paying out their cables in a controllod manner, the template structure may be controflably lowered to rest on its footings on the seabed. With the three-legged template structure, a possible arrangement is to use three winches such that there is one attached above each footing to more accurately control the positioning and landing of the template structure on the sea bed.

After the structure has settled securely on the sea bed when delivered from a dedicated catamaran barge, there are two possibilities for subsequent usage; firstly, the barge may be moored to the structure using a mooring arrangement capable of holding it in place despite the rise and fall of the sea surface under tidal influence (suitable fenders being provided to prevent damage due to inevitable impacts between the barge and the template structure); and secondly, the barge may be manoeuvred away from the structure by tugs.

Recovery of the template structure alter drilling and placing of the pile or piles is completed involves simply reversing the procedure just described.

The conventional method for placing piles in areas with strong currents is generally to use a jack-up barge to provide a stable platform to drill from.

It is convenient to note that the template structure of the invention has the advantage over jack-up barges that, firstly, the elongate leg members serve a dual purpose as conductor tubes for drilling through (a jack-up barge needs legs and additional conductor tubes) thereby reducing the overall drag in strong currents. Secondly the leg members can have strakes or streamlined profiles as they do not need to be withdrawn through a tight orifice as for a jack-up barge's legs. This sItuation can inhht vortex shedding which is a major cause of instability for a jack-up barge standing In a strong current. The leg members can also be crossbraced which greatly Increases the strength and resistance to buckling compared with cantllevered jack-up barge legs and, moreover, the cross-bracing can Indude hydrofoiis to improve stability in strong currents by creating down force. Lastly, this invention consists of what is sometimes called a "dumb structure" with no moving parts; hence It Is more robust, potentially fasterat complellng the required operations and a lot less costly than a jack-up barge capable of standing In similar depths of water

BRIEF DESCRIPTiON OF THE DRAW1NGS

For a better understanding of the invention and to show how to carry the same into effect, reference will now be made to the accompanying drawings inwhlch; FIgure 1 schematIcally Illustrates in Isometric view an embodiment of a template structure Incorporating the concepts of the Invention and when the template structure is In position on the sea bed with a cutaway of the sea (or other water) surface as indicated to illustrate the immersion depth; Figure 2 schematically illustrates a specialised twin-hulled (catamaran) type vessel capable of transporting the complete template structure shown in Figure 1 betweenitshullsasshown;and Agure 3 schematicaUy shows how the twin-huUed vessel can be used to lower the template structure so that it can stand on the sea bed (or any other b&ow water surface).

DESCRIPTION CF THE CONTENT OF THE DRAWINGS

Referring now to Figure 1, the embodiment of the template structure shown therein involves three upstanding tubular elongate leg members I with three vertically adjustable footings 2. In the embodiment shown, each footing 2 is shown, by way of example, with a pair of hydraulic rams 2a, but other methods of vertical adjustment may be used. The aforementioned footings 2 are mounted on outrigger extensions 2b from a chassis frame 3 which can carry ballast or kentledge 4.

A working platform 5 is positioned at the top region of the template structure. This platform 5 will normally carry personnel plus a crane or cranes, power plant, grouting systems, etc., (none of these being illustrated).

Crossbracing members 6 may be used to reinforoe the template structure and to improve its stiffness. This crossbracing may also take the form of or serve to carry hydrof oils (not illustrated) orientated to create down force in strong ourrents to improve stability.

A single drilling rig 7 with a small crane 8 is shown mounted on top of one of the tubular elongate leg members I. ln Figure 1, only one such drilling rig 7 and associated crane 8 is illustrated, since in this example they may be moved from one leg member I to the next to enable sequential drilling.

However, in praotioe it may be more cost-effeotive to have a driliing rig 7 and associated crane 8 mounted on each leg member I so that simultaneous drilling and pile insertion can take place to speed up the installation operation.

Some details that are likely to improve the performance of the system as so tar disclosed includes strakes 9 set vertically along the upstream and downstream sides of each leg 1 to InhIbit vortex shedding. These strakes 9 could also take the form oF a spiral as used on many tail chimneys to serve the same purpost Mernatlvely, other than circular cross-sections of the leg members 1 may be used (not Illustrated) such as streamlined (ellIptical) or straight edged (diamond) proFiles whIch would not produce vortices. There lseisoanextenslonslaevelothatcanbeloweredthroughthetubularleg once the structure is positioned to protect the drill string when passing through the space between the lowermost ends of the tubular leg members 1 and the ground surface of the sea or the river bed SB. Alternatively as Is Illustrated, such a sleeve 10 could be mounted externally of the lower end of the associated tubular leg member 1 gIven sufficient space.

Referring now to Figure 2, a specialised twin-hulled (catamaran) type vessel capable of transporting the complete template structure shown in Figure 1 betweenltshullsisshown.Anadvantageofsuchavesselisthatitcanbe desIgned to have low hull drag In fast moving water compared with conventional barges.

FIgure 3 shows how the catamaran barge can lower the template structure sothatitcanstandontheseabed(oranyothergroundsurlacebeneatha liquid body). The barge may then remain moored to the template structure for the duration of the drilling operations or It may depart and return later to collect the template structure after drilling has been completed.

Claims

CLAIMS1. A temporary template structure for the erection of one or more columnar members in a ground surface beneath of a column of liquid, said template structure including an elongate leg member extending substantially perpendicularly from a base structure, and said leg member serves to support a platform arranged substantially parallelly to said base structure.
2. A temporary template structure according to claim 1, wherein said one or more columnar members are one or more piles.
3. A temporary template structure according to claim 1 or 2, wherein said platform comprises a drill unit mounted thereon.
4. A temporary template structure according to claim 3, wherein an end portion of said drill unit forms one of said columnar members.
5. A temporary template structure according to any preceding claim, wherein said elongate leg member is tubular in form.
6. A temporary template structure according to claim 5, wherein one of said columnar members is moveable through the elongate tubular leg member.
7. A temporary template structure according to any preceding claim and including a plurality of elongate leg members.
8. A temporary template structure according to claim 7, wherein said plurality is three.
9. A temporary template structure according to any preceding claim, and further comprising a grouting system provided on said platform, the arrangement being such that said grouting system delivers grout to the region of the ground surface to fix any columnar member mounted therein.
10. A temporary template structure according to any preceding claim, wherein said base structure comprises a support for ballasting material.
11. A temporary template structure according to any preceding claim, wherein said base structure includes a puraty of support footings extending below the base structure and arranged to rest upon the ground surface.
12. A temporary template structure according to any preceding claim, wherein said base structure comprises leveling devices.
13. A temporary template structure according to 12 as appended to claim 11, wherein said leveling devices are attached to said support footings.
14. A temporary template structure according to any preceding claim, wherein the or each elongate leg member includes strakes attached to the upstream and downstream sides.
A temporary template structure according to any one of claims 1 to 13, wherein the or each elongate leg member has a load-reducing cross-sectional profile.
16. A temporary template structure according to any one of claims 7 to 15, and further comprising bracing members between said plurality of elongate leg members.
17. A temporary template structure according to claim 16, wherein said bracing members include hydrofoil devices mounted thereon.
18. A temporary template structure according to any preceding claim, and further comprising buoyancy means.
19. A temporary template structure according to any preceding claim, and further comprising a sleeve device slidingly engaeable with a lower end region of the or each elongate leg member.
20 A method comprising transporting a temporary template structure to a desired location in a body of liquid, the template structure including a base structure, an elongate leg member extending substantially perpendicularly from said base structure and a platform arranged substantially parallelly to said base structure, submerging the base structure tobesupportedproximaitoagroundsurfacebeneathsaidbodyof liquid and arranging the platform to be supported substantially above an upper surface of the column of liquid distal from the ground surface.
21. A method according to claim 20, wherein said transporting includes supporting the temporary template structure above an upper surface of the body of liquid and between first and second hulls of a catamaran vessel.
22. A method according to claim 21, wherS said submerging Includes a plurality of winch devIces mounted on the catamaran vassal with their assocIated cables connected to the temporary template structure for the controlled submerging of the temporary template structure.
23. Amethodaccordlngtoanyoneofclaims2oto22,andfurther comprising performing an operation at said temporary template structure.
24. A method according to claim 23, wherein said operation comprises drIlling one or more holes Into the ground surface
25. A method according to claim 24, and further comprising Inserting respective columnar members In drilled holes In the ground surface.
26. A method according to any one of claims 23 to 25, and subsequent to said performing, recovering said temporary template structure and further transporting It to another desired location.
27. In combination:- * a catamaran vessel having first and second hulls, and * a temporary template structure supported between the first and second hulls and including an elongate leg member extending substantially perpendicularly from a base structure, said base structure including a frame, and said leg member serves to support a platform arranged substantiaily parallelly to said base structure.
28. A combination according to daim 27, and further compnsng a puraty of winch devices mounted on the catamaran vesse' with their associated cab'es connected to the temporary temp'ate structure.
29. A temp'ate structure for p'acement at a desired ocation in a body of water inc'uding a base structure for supporting an elongate tubu'ar eg member of sufficient length to support a p'atform ocated substantial'y above the surface eve of the body of water, wherein said p'atform serves to mount at east one driffing unit, said drifi unit comprising a driU string for driving a co'umn-receiving ho'e in the ground surface be'ow the body of water upon which the template structure is supported.
30. A method of inserting one or more co'umns into a ground surface below a body of water comprising supporting by an ebngate tubu'ar eg member a template structure upon the ground surface at a desired ocation, said temp'ate structure comprising a submerged base structure and a p'atform ocated substantiay above the surface eve of the body of water, activating a dri'l unit mounted on said platform via an associated dril' string so as to bore a co'umn-receiving hose in the ground surface, and introducing a co'umn into said hose through said e'ongate tubu'ar eg member.
31. A temp'ate structure as substantiaUy hereinbefore described with reference to the accompanying drawings.
32. A method as substantiaUy hereinbef ore described with reference to the accompanying drawings.