EP1492699A1

EP1492699A1 - Submersible watercraft

Info

Publication number: EP1492699A1
Application number: EP03721147A
Authority: EP
Inventors: Joop Roodenburg
Original assignee: Itrec BV
Current assignee: Huisman Equipment BV
Priority date: 2002-04-10
Filing date: 2003-04-10
Publication date: 2005-01-05
Anticipated expiration: 2023-04-10
Also published as: NO330075B1; ATE368611T1; AU2003224498A1; WO2003086852A1; NO20043671L; EP1492699B1; DE60315276D1

Abstract

A method for erecting an object, in particular a lifting frame, comprising the steps of: providing a floatable object having a base and a top; providing a submersible vessel; placing the floatable object on the vessel; transporting the vessel with floatable object to a desired location; ballasting the vessel to permit the floatable object to float; securing the base of the floatable object to the vessel; securing a hoist line between the floatable object and a winch on the vessel; winching the hoist line and thereby raising the floatable object top from the water while the base remains secured to the vessel. In a preferred embodiment the floatable object is a lifting frame, in particular an A-frame. Preferably the vessel is a catamaran.

Description

Submersible watercraft

A first aspect of the present invention relates to a method for erecting an object, in particular a lifting frame, wherein a submersible vessel is employed. The first object of the invention also relates to a combination of a submersible vessel and the object to be erected.

Experience with oil and natural-gas exploration, production and transmission in the North Sea has shown that, because of the frequent bad weather, surface vessels can have difficulty in moving a rig or platform from the shore to an offshore location. Considerable time can be spent waiting out the storms for calm water which is important when transporting a heavy device, such as a platform. This waiting causes a major loss of working time for surface vessels engaged in any North Sea project or project where turbulence of the water is an issue.

Moving a large platform in pieces is also expensive and time consuming, as construction now must be performed at sea, in less than stable working conditions . The present invention was developed to enable the transport of rigs and drilling platforms even in rough sea conditions by submerging to one of two levels, while retaining the option to operate in a normal draft.

German Offenlegungsschrift 23 56 537 discloses a catamaran surface vessel having a submersible gondola located between the two hulls of the catamaran. The catamaran remains afloat when the gondola is lowered for underwater travel. The submersible gondola has a torpedo-like shape widely used for self-propelled underwater craft because of its low resistance to motion for the volume of water displaced, relative to other shapes. Although the catamaran, by virtue of the form stability provided by its two spaced-apart hulls, has a high resistance to capsizing, it is nonetheless susceptible to bad weather and rough seas as are other surface vessels .

U.S. Pat. No. 1,757,174 to Douglas discloses a seagoing vessel having five pontoons: a cabin pontoon, two waterline pontoons, and two power pontoons . The two waterline pontoons are disposed below and to either side of the cabin pontoon. A power pontoon is disposed below each waterline pontoon. The vessel of U.S. Pat. No. 1,757,174 is a surface vessel. Only the power pontoons, located beneath the waterline pontoons, are submerged when the vessel is under way. Consequently, the vessel is also affected by heavy seas .

The first aspect of the invention relates to a method according to claim 1. Dependent claims disclose preferred embodiments of the method.

The first aspect of the invention also relates to the combination of claim 10. Dependent claims disclose preferred embodiments of the combination.

The first aspect of the present invention relates in a preferred embodiment to the erection of a lifting frame, such as an A frame, to be used in offshore operations, such as well maintenance, drilling, or other maritime operations, such as bridge construction.

In a preferred embodiment the vessel employed in the first aspect of the invention is a submersible catamaran having two floats disposed generally parallel to and spaced apart from each other.

A second aspect of the invention relates to a gantry system on a catamaran and in particular to a method for constructing the gantry system at sea on said catamaran according to claim 18.

The second aspect of the invention also relates to the catamaran of claim 19 which includes a gantry to be constructed according to the method of claim 18.

The third aspect of the present invention relates to a method to the commission and decommission of a topsides using a submersible catamaran.

This method involves submerging the catamaran under the intended topsides to be installed then rising by deballasting, to lift the topsides, then while either partially submerged or at normal draft, to transport that topsides to a new position, then by ballasting and positioning to depositing that topsides on the new structure.

The third aspect of the invention also relates to a method for picking up a topsides for decommissioning using a load lifting system which is integral to the vessel, carrying the topsides and redepositing the topsides using the same lifting system.

A method has long been needed for moving large topsides in one piece, in less than stable seas. The third aspect of the present invention was developed to enable the transport of rigs and drilling platforms even in rough seas by providing a vessel, which can move while submerged at one or more drafts, or to transport at normal draft.

The third aspect of the invention provides methods according to claims 20-33.

A fourth aspect relates to a vessel, preferably a catamaran, comprising a crane for lifting objects.

The fourth aspect of the invention provides, according to claim 34, a submersible vessel having a submersible vessel hull and a crane supported on said hull for lifting objects, wherein the crane is adapted to be floatable, such that when the hull of the vessel is submerged the crane floats with respect to the vessel hull and wherein the hull provides multiple crane positions for supporting the crane on the said hull, such that the floating crane is displaceable from one crane position to another crane position.

In a preferred embodiment the vessel has one or more associated buoyancy members releasably attachable the crane so that the crane is rendered floatable.

In a further preferred embodiment the vessel is a catamaran having spaced parallel floats and a support surface across the top of the floats and spanning the gap between the floats, wherein said support surface in the area of the gap is partly formed by a buoyant hatch, which is hatch is removable from the support surface and is adapted to be secured to said crane to render the crane floating.

A fifth aspect of the present invention relates to method according to claim 37 for operating a catamaran which is adapted for lifting loads.

The man skilled in the art will appreciate that the aspects of the invention can be realized separately or in various combination.

The aspects of the invention will now be explained in further detail referring to the drawings showing, non-limitative examples. In the drawings :

FIG 1 is a top view of the catamaran with ballast systems.

FIG 2 is a starboard view of the catamaran with two moveable columns . FIG 3 is a bow on view of the catamaran showing the air gap.

FIG 4 is a top view of the catamaran showing the bow structure as rounded triangular shapes .

FIG 5 shows three typical drafts for the catamaran.

FIG 6 shows a vertical positioning system usable on the catamaran disposed in a moveable column.

FIG 7 shows the catamaran from the stern view using the vertical positioning system on an object at sea.

FIG 8 is a top view of the catamaran using the horizontal positioning system.

FIG 9 shows the catamaran wherein two of the moveable columns have been moved from positions on extreme ends of the submersible floats to a center area of the solid support structure.

FIG 10 is a top view of the catamaran with the hatch disposed across the bow.

FIG 11 is a stern view of the catamaran with a lift operation occurring.

FIG 12 shows an A-frame with floating devices mounted, positioned on the catamaran at normal draft.

FIG 13 shows the catamaran being ballasted down into the water and the A-frame floating over the solid support surface.

FIG 14 shows the A-frame of FIG 12 floated off of the catamaran.

FIG 15 shows the floating A-frame secured to the stern of the catamaran .

FIG 16 shows a luffing tackle secured from one end of the A-frame to a winch on the catamaran.

FIG 17 shows an erected A-frame with a semi-submerged catamaran.

FIG 18 is a view of the self-erecting gantry as erected on a catamaran .

FIG 19 shows the first step of erecting the self-erecting gantry.

FIG 20 shows the second step of erecting the self-erecting gantry.

FIG 21 shows the third step of erecting the self-erecting gantry.

FIG 22 is a view of the catamaran with a barge carrying a topsides prior to load transfer.

FIG 23 is a view of the catamaran carrying topsides on the detachable, moveable support columns while semi submerged.

FIG 24 shows a crane disposed on the catamaran.

FIG 25 shows displacing the crane of FIG 24 on the catamaran.

In FIG 1, a catamaran (2) is shown having a bow (4) and a stern

(6) . The catamaran has a first submersible float (8) and a second submersible float (10) .

The first and second submersible floats (8) and (10) each have a similar construction of bow, midsection and stern section, the latter being referred to hereafter as the tail.

In particular, the first submersible float has a first float rounded triangular bow (50) , a first float midsection (54) , a first float tail (58), and first float stern (62). The second submersible float (10) has a second float rounded triangular bow (52) , second float midsection (56) , second float tail (60) and second float stern (64) .

The first and second submersible floats (8) and (10) are disposed in a parallel relation to each other along a center line (158) . In one embodiment, the first float tail (58) and the second float tail (60) have a tapered shape. Alternatively they can be of a rectangular design, however the tapered shape enables easier positioning of the catamaran when engaging objects at sea.

FIG 1 also shows that each submersible float has a ballast system. First submersible float (8) has ballast tank (34) and second submersible float (10) has ballast tank (35) .

An air gap (13) which is shown in better detail in later Figures, is present between the first and second submersible floats and the solid support surface (12) . A slot opening (15) is disposed between first and second submersible float tails. The slot opening in a preferred embodiment is between 10 and 80 meters in width and 10-80 meters in length. In a most preferred embodiment the slot opening (15) is 50 meters in width. Preferably, the slot opening (15) has a U-shape. The slot opening (15) is sized to position at least partially around a structure in a marine environment, such as around a jacket or a spar or similar deep draft floating caisson structure as shown in more detail in FIG 7. Other structures which could be positioned in slot opening (15) include a floating platform, a fixed leg platform or another floating vessel.

FIG 2 is a starboard view of the catamaran, shows that the support surface (12) forms a top on the first and second submersible floats. This solid support surface (12) can support very heavy loads. The catamaran has two towers or columns which are disposed generally above the hulls approximately in a longitudinal symmetry plane.

The two hulls and the columns are rigidly interconnected by the support surface (12) . The towers or columns can contain propulsion and control mechanisms, crew accommodation and other equipment, such as ROV's, diver work chambers, pipeline repair gear or other operating equipment .

Also the catamaran has load supporting moveable columns (14,16) and (17,19) which are disposed on the support surface (12). Additional moveable columns are also contemplated as usable on this catamaran. These load supporting moveable columns can support very heavy loads, such as a top sides, or objects, such as plates of steel or a hatch can be placed on the load supporting moveable columns and then a load placed on the hatch. These load supporting moveable columns can also be used as a lifting device in combination with a hatch of the catamaran.

Returning to FIG 1, four load supporting moveable columns are shown, as (14) , (16) , (17) and (19) . In a most preferred embodiment, four moveable support columns are contemplated, two disposed on the first submersible float and two disposed on the second submersible float. However, it should be noted that between 2 and 10 load supporting moveable columns could be used on a catamaran. These columns can be skiddable on the support surface (12) . Alternatively, these columns can be detachable from the support surface .

The support columns are detachably fitted on the floats . This has the advantage that the support columns can be removed from the vessel at the point in time when they are not needed. This makes a difference in weight and, furthermore, space is made free on the deck in this way. Furthermore, it is advantageous if the position of the support columns on the floats is adjustable. The construction of the catamaran is so rigid and so strong that the position of the support columns on the floats can be freely chosen. The support columns can be placed in an optimum position, depending on the load that has to be transported. The support columns can be positioned close to the stern of the catamaran.

The one or more fixed columns, with the crew accommodation etc. therein, are preferably located at the bow of the catamaran. Two fixed columns can also be disposed on the submersible floats, preferably one on each float.

It is possible that the open space between the two floats is filled by hatches in order to increase the effective surface area of the deck. Provision is made that these hatches can be fixed to the side of the floats. In this case the volume of the vessel is appreciably increased at this location. As a result the lifting capacity of the catamaran will be increased at the location of the hatches.

FIG 2 shows one of the two fixed columns, the first fixed column (18) disposed on the submersible float (8).

FIG 3 shows the second fixed column (20) disposed on the second submersible float (10) . These fixed columns are contemplated to be single hulled or double hulled. Double hulling is helpful if the columns should contain a fluid that is harmful to the environment. This construction helps to create an environmental friendly vessel.

Returning to FIG 2, the ballast system (34) is shown disposed in the submersible float (8) . It is contemplated that at least two ballast systems are used, one for each submersible float. FIG 1 shows the preferred positioning of each of the two ballast tanks which would be used in this vessel. These ballast systems are used to raise and lower the catamaran with respect to the waterline. The ballast systems can be used to keep the catamaran at first, a normal draft, or second, a slightly submerged draft, wherein water fills the air gap (13) between the first and second submersible floats (8) and (10) and the solid support surface (12) is above the water level, or third, a lower draft, wherein between 1 and 16 meters of water covers the solid support surface (12) .

These three drafts are explained in more detail with reference to FIG 5. It is contemplated that the first and second ballast systems (34) and (35) can be used to raise and lower the catamaran between 10 and 90 percent of the overall height of the catamaran.

Returning to FIG 2, an optional propulsion system comprised of rotatable propellers and bow thrusters is shown for one of the two submersible floats. In particular, reference number 38 is a rotatable propeller connected to an engine (37) , and reference numeral (39) is a thruster as is reference numeral 42. At least three propulsion devices can be located in each submersible float as an option. The equipment for operating these devices can be contained in the fixed column (18) and (20) or located in the floats.

FIG 3 provides additional detail that the fixed columns (18) can contain crew accommodations (92) and/or a bridge command center, such as a navigational bridge (74) for piloting and commanding the vessel. The fixed column can contain catamaran operational equipment (93) . The fixed columns can also support a helipad or second deck (72) as shown in this Figure. It is contemplated as an option that each fixed column could support different structures. (74) .Also notable in FIG 3 is the air gap (13) disposed between the two submersible floats.

FIG 4 shows a top view of the catamaran with the airgap (13) and the slot (15) as well as the support deck (12) in a position where the slot (15) is not covered by hatches. In this Figure, the two fixed columns (20) and (18) are shown disposed on the submersible floats . Figure 4 shows the bow structure having the unique rounded triangular shape for each submersible float. The edges are shown as reference numeral 200 for float (8) and reference numeral (202) for float (10) .

FIG 5 shows the way in which the catamaran can be submerged to at least 3 different draft depths. The first depth is shown as reference numeral (180), the second depth is shown as reference numeral (182) and the third depth is shown at reference numeral

(184) . It is contemplated that the vessel can move at any of these depths .

Figure 6 shows one element of the vertical positioning system (24) which is installed in at least two of the moveable columns and used for securing the catamaran to an object at sea. A first line (134) connects to an object at sea (1000) . One end of this line (134) is secured substantially vertically to an object at sea (1000) . The angle of attachment is usually not more than between 5 and 30 degrees from the vertical. Typically a second line (135) is used, as shown in FIG 7 and is also secured on one end, substantially vertically, no more than between 5 and 30 degrees from the vertical, to the same object at sea.

The object at sea (1000) is fitted into the opening slot (15) of the catamaran and secured with both lines. FIG 7 shows the object at sea secured in the opening slot (15) .

FIG 7 is a stern view of the catamaran wherein, the submersible hull (8) and the submersible hull (10) can be seen, as well as two moveable columns (14) and (16) each containing a vertical positioning device with motion compensation system.. Specifically, moveable column (14) contains the first vertical positioning device (24) and moveable column (16) contains the second vertical positioning device (200) .

Returning to the detail of FIG 6, the vertical positioning system is a motion compensation system (138) disposed in the first load supporting moveable column (14) . The other end of first line (134) engages this motion compensation system. In the second load supporting moveable column 16, an identical second motion compensation system is located and connected to the other end of the second line (135) (shown in FIG 7) .

The first and second motion compensation systems (138 and 200) each comprises the same elements, which are shown in detail in FIG 6. Specifically the systems include a winch (77), the line (134 or 135) connected to the winch and vertically connectable to the object at sea (1000) , a tension measuring device (79) connected to the line; a motion control device (80) connected to the line and winch for monitoring and controlling tension on the line. Sheaves or rollers or wheels 104a and 104b can be used to assist in the tensioning of the line. These rollers are preferably mounted at the top of the moveable columns, and the tensioning devices are mounted at the bottom of the device. The motion compensation systems also each comprise at least one pressurized cylinder (81) containing pressurized gas to control the system and assisting in the tensioning. Between 1 and 8 or more winches can be used in each motion compensation system.

A horizontal positioning system is also used on the vessel. This horizontal positioning can be a dynamic positioning system. FIG 8 shows the horizontal positioning system holding a spar or floating deep draft cassion vessel in the opening slot (15) . The horizontal positioning system preferably consists of at least three maneuvering lines (25, 26, and 28) although four are shown in FIG 8, with the fourth maneuvering line having reference numeral (33) . Each line is connected on one end to a maneuvering winch. Line (26) connects to winch (19) , line (25) connects to winch (30) line (28) connected to winch (23) . The other end of each line connects to the object at sea (1000) . It should be noted that if the fourth line (33) is used, it would be connected to a maneuvering winch (31) . Each winch is disposed in a load supporting column. Winch (23) is in column (17) , winch (19) is in column (29) , winch (30) is in column (16) and optional winch (31) is in column (14) .

A controller (130) for orienting the catamaran relative to the object at sea (1000) is electrically connected to the winches and the motion compensation systems . The controller monitors the tension on the maneuvering lines and the controller initiates winch pay out of the maneuvering line when load on any one of the maneuvering lines exceeds a first preset limit. The controller initiates the maneuvering winch tensioning of the maneuvering lines when tension on any one of the maneuvering lines falls below a second preset limit.

All winches are used to reduce the relative motion between the two bodies. When the bodies move away from each other, the winches go to a high preset tension. When the bodies move towards each other, the winches go to a low preset tension.

The vessel can include a propulsion system. However, this vessel may be propulsion-less, and simply be towable and work within the scope of the invention for lifting, transport and maintenance of objects at sea.

FIG 9 shows one embodiment of a propulsion system usable on the vessel. A mirror image for the port side of the vessel is contemplated for this propulsion system. This starboard side has a first engine (37) in the first submersible float (8) driving a first rotatable propeller (38) . A second engine is the second submersible float for driving a second rotatable propeller also disposed on the stern of the second submersible float.

The propulsion system can optionally comprises a first bow thruster (42) disposed in the bow of the first submersible float (8) connected to the propulsion system, and a second bow thruster (44) disposed in the float connected to the propulsion system. Returning to FIG 7, another embodiment contemplates that the propulsion system further can comprises a first stern thruster (46) disposed in submersible float (10) connected to the propulsion system and a second stern thruster (48) can be disposed in the second submersible float (8) . These two thrusters can be used with the two rotatable propellers previously described. In still another embodiment, two stern thrusters can be used in each submersible float. Figure 7 shows the 4 stern thruster embodiment with the additional stern thrusters noted at 46a and 48a. Essentially, the catamaran can comprise a propulsion system consisting of a plurality of bow and stern thrusters.

The present invention is contemplated to include one or more load supporting hatches. The support surface (12) can comprises at least one removable hatch. In a preferred embodiment, the hatch can float. FIG 1 shows removable hatch (21, 152, 154 and 156) disposed over the opening slot (15) .

In a safety mode for moving the catamaran, it is contemplated that the removable hatch can be placed between the bows of the first and second submersible floats to prevent water from coming over the solid support surface (12) . FIG 10 shows the hatch 21 disposed across the bows of the vessel.

The vessel can either place a topsides or remove a topsides, jacket or similar structure. FIG 11 shows one of the lifting embodiments for the vessel, which can be used to lift a small structure from a jacket. In this embodiment, a hatch (21) is disposed over the two load support columns (16) and (14) for carrying a load (400) using the two winches and two motion compensation systems and the vertical compensation system previously described. Other lifting devices can also be used, such as an A-frame, a gantry, or a crane.

Figures 12-17 show how an A-frame (300) can be erected on the catamaran e.g. for use in installing structures at sea or for decommissioning a topsides or jacket. To erect this A-frame, first, the A-frame (300) is placed on the catamaran (2) . Prior to placing the A-frame on the catamaran, removable floats (302) , (303) (304) and (305) are secured to the A-frame (300) . In the preferred embodiment, the A - frame (300) is loaded such as using a land based crane, directly on the support surface (12) .

To erect the A-frame (300) , the catamaran (2) is submerged to a draft wherein the A-frame (300) floats over the vessel, as shown in FIG 13.

The A-frame has a top (308) and a base (306) . The vessel (2) has a connection point (312) to engage the base (306) of the A-frame. The A-frame (300) is then floated off of it's position over the support surface (12) in proximity to the vessel while slightly submerged, wherein water comes on deck, as shown in FIG 14.

FIG 15 shows that the vessel (2) is deballasted to a normal draft and the base (306) engages the connection point (312) to obtain a pivot connection between the two.

FIG 16 shows that a luffing tackle (314) is used to engage the A- frame (300) . Also a winch (316) disposed on the deck of the vessel (2) and a hoist line (317) connects the top (308) with the winch (316) .

FIG 17 shows that the vessel (2) is ballasted in the bow so that the weight of the vessel permits the A-frame to have a position where the top (308) is erect while connected at the base (306) to the connection point (312) . The vessel then can be ballasted to a normal draft and the A-frame (300) used to decommission a topsides or provide lifting for a large object at sea.

It should be noted that this A-frame could be another type of frame, and that the floating or floatable hatches are secured only on one side of the frame. It is further contemplated that the lifting frame or A-Frame could instead be an oil derrick.

This method contemplates that the catamaran can be moved not only while at a normal draft, but also while semi-submersed with the erected lifting frame in the upright position.

This method contemplates that the lifting frame (300) can be modular in construction or alternatively, a one-piece construction.

In this method, the catamaran can be moved by self propulsion or by towing.

FIG 18 shows a constructed gantry. The gantry (428) has a first leg (500) and a second leg (502) , which support a top (21) , which is in the preferred embodiment, a floatable hatch that is usually disposed over the opening slot (15) . The top (21) supports a hoist system, which can include in one embodiment, a first lift (416) and a second lift (504) which can be secured to a jacket or other object at sea (1000) using at least lines 506 and 508 respectively. Two lines per lift are the preferred embodiment, as shown in FIG 18 with lift 416 having lines 506 and 507 and lift 504 having lines 508 and 509. The gantry 428 can utilize the vertical and horizontal motion compensation systems of the catamaran vessel, as shown in FIG 18 to stabilize the object at sea (1000) while the gantry lifts the object at sea from the sea bed or other installation. Specifically each system can include a winch, a line and sheaves mounted in the load supporting column.

FIG 18 shows column 14 having a winch 404, line 456 and sheave 446 wherein line 456 secures to the object at sea (1000) . Column 16 has a winch 406, line 454 and sheave 448 for securing the line 454 to the jacket or object at sea (1000) . The other two columns (not shown) have identical structures and features for securing to the object at sea. It is preferred that the legs of the gantry are supported between the four load supporting moveable columns of the catamaran. Detail in the construction of the gantry at sea is provided in more detail in the following figures.

The FIG 18 shows the catamaran at a normal draft for transport of the jacket (1000) ; however, the catamaran can submerge slightly in order that the deballasting of the vessel and the structure of the gantry to minimize vessel movements. One specific method of using the erected gantry, contemplates submerging the catamaran while positioned around the jacket or object at sea, attaching the lifts to the top most portion of the jacket. Tensioning the lifting lines. Attaching to the object at sea, the horizontal and vertical positioning lines which are secured to the motion compensation systems located in each of the moveable load supporting columns . Deballasting the catamaran to raise the ship with the object at sea secured to the lift and/or means, and then additionally lifting, with the winches, if needed, the jacket with the lifters to further raise the jacket while maintaining the position of the jacket in the opening slot (15) . Transporting the jacket either at normal draft, or _.if the seas are very rough, at a semi submerged depth to a shore location or location for installation in another portion of the sea.

FIG 19, 20 and 21 shows the steps for the method for constructing the gantry at sea. First a top (21) is formed as shown in FIG 18 between two load supporting moveable columns (14) and (16) . A first lift (416) and a second lift (504) are secured to the top (21) , which is here formed of a first floatable hatch of the vessel (2) . Sheaves, pulleys and lines are used to secure the lifts to the top (21) and each lift is secured to a moveable load supporting column. In FIG 18, lift (416) is secured to column (14) and lift (504) is secured to column (16) .

FIG 19 shows a plate or similar support structure (510) disposed between two of the load supporting moveable columns (16) and (19) forming a lifting support structure. Lifting systems are secured to this lifting support structure, specifically; first and second lines second lifting support structure (not shown) is disposed between the remaining two load supporting moveable columns (14) and (17) to create a second lifting support structure and two lifting systems from these two columns are secured to this second lifting support structure. The third and fourth lifting systems are identical to the first and second lifting systems.

In contemplation of the construction of the gantry, the first, second, third and fourth moveable columns each have a fastener disposed near the top of the column. Specifically, columns 16, and 19 have first fastener 442, second fastener 420 and as shown in FIGURE 19. The remaining columns have similar fasteners positioning in a similar place which are not shown.

The gantry top (21) is raised by the first and second lifting support structures and fastened to the top of the four moveable support columns. FIG 20 shows the first gantry leg being raised by the lifting support structure 510. The first and second lifting support structures are first down on the level of the solid support surface (12) forming a first space (428) between the load supporting movable columns (16) and (19) . In the first space (428) and on that first lifting support structure, a first gantry leg piece (432) is placed. In the second space on the second lifting support structure, between the third and fourth load supporting moveable columns, a second gantry leg piece is placed. The leg pieces are raised. FIG 21 shows the first gantry leg (432) fastened to the top of the columns (16) and (19) using the fasteners (422) and (420) after raising, and the first lifting support structure (510) lowered forming a space (428) for insertion of the next gantry leg piece.

It is contemplated in one embodiment that the gantry top is lowered onto the first and second gantry leg pieces and locked to the first and second gantry leg pieces forming a first segment. The first segment is lifted with the first and second plates and the first and second gantry leg pieces are fastened to the fasteners on the top of the first, second, third and fourth load supporting moveable columns. Alternatively, the third and fourth gantry legs are lifted and locked on to the first and second gantry legs fastened to the top of the movable columns forming the first segments. The segment is then lifted and locked on the top columns .

Next, the first and second plates are lowered creating again the first space and the second space. In the first and second spaces are disposed third and fourth gantry leg pieces. The first segment is lowered down to the top of the third and fourth gantry leg pieces and locked to the third and fourth gantry leg pieces forming a second segment, the second segment is lifted with the first and second plates and the second segment is locked to the fasteners disposed on the top of the first, second, third and fourth load supporting movable columns . Alternately, the 3^rd and 4^th gantry legs are lifted and locked to the first segment forming a second segment. The second segment is than lifted and fastened to the top of the columns.

The first and second plates are again lowered forming the first and second spaces and the process is repeated until the gantry is built.

In a possible embodiment the gantry is adapted to be displaceable over the support surface of the vessel.

Referring to figures 22 and 23 the third aspect of the invention will be explained in detail.

The third aspect of the invention relates to a method for installing topsides to form an offshore platform, with the topside initially at a wharf and then at an intended installation at a location remote from the topside.

Initially, the method comprises a series of steps, which can include placing a topside on a transport wagon; rolling the transport wagon onto a barge and positioning the topsides on the barge wherein a portion of the topsides extends out over opposing sides of the barge.

Next, topsides support structures can be placed on the barge. The topsides are then lowered onto topside support structures enabling the wagon to be rolled from under the topsides and off of the barge.

The barge is then moved near to a submersible catamaran comprising having a bow (4) and a stern (6) as shown in FIG 1.

FIG 22 shows some of the features of the method for lifting and transporting a topsides.

FIG 22 shows a topsides already placed on a barge. In a preferred method, the first step consists of: placing a topsides (301) on a barge (302) . The barge (302) is then maneuvered near the catamaran (2) . The catamaran has positioned the first and second moveable columns (14) and (16) at the stern of the vessel opposite the opening slot (15) . Two additional moveable columns, not viewable with this FIG, are disposed in front of the first and second columns, forming a four-column square or rectangle around the slot opening (15) .

One or more removable hatches are taken off of a position covering the opening slot (15) thereby forming an unobstructed opening and placed on the solid support surface (12) . Each of the four corners of a hatch is connected to the vertical positioning system lines and winches disposed in each of the columns. Here lines (134 and 136) are only viewable, but it is contemplated that all four lines are used. The catamaran is then ballasted to a position below the water's surface (303) .

The barge (302) is sailed into the opening over the hatch (21) .

The first and second ballast systems are then used to raise the catamaran with respect to the waterline. The base (304) of the topsides is positioned over the tops of the four load supporting moveable columns (14,16,17,19).

The vertical positioning system used for this method is essentially a securing system for securing the catamaran to a topsides or other object, and it comprises : (i) tensioning lines; (ii) a winch; (iii) a motion compensation system (25) disposed in each load supporting moveable column.

A control means is used to. enable the securing systems to cooperatively tension the lines.

The catamaran is then raised further, enough to transfer load from the barge to the load supporting moveable columns. The hatch (21) is then lowered with the securing system without the topsides. The catamaran is then lowered permitting the barge to float freely.

The barge is then sailed away from the catamaran.

The catamaran then transports the topsides either at normal draft or in a semi-submersed state to minimize motions on the catamaran.

FIG 23 shows the catamaran transporting the topsides (301) while at a semi-submerged draft.

An alternative embodiment of this invention, involves moving the topsides using a wagon onto the barge, keeping the topsides on the wagon, and removing the topsides from the wagon onto the catamaran. The method can also comprise using an element between said topsides and the topsides supporting moveable columns to dampen movement between the topsides and the catamaran. The element can be a rubber disc or elastomeric material.

In an embodiment, there can be between 4 and 16 lines used in conjunction with the line of the motion compensators. It is contemplated that a barge with subsea equipment such as subsea hoisting systems, moorings, suction piles can be sailed onto the support surface (12) while the catamaran is submerged, then the catamaran can be raised and the barge can be supported on the support surface (12) .

The fourth aspect of the invention will now be explained referring to figures 24 and 25.

FIG 24 shows a crane (430) secured to the center of the catamaran (2) for lifting objects at sea.

FIG 25 shows how that same crane (430) can be moved to a different position on the catamaran using the floatable hatches. In this embodiment, it is contemplated that two floatable hatches can be used, (438) and (440) to slightly elevate the crane while the catamaran is semi-submerged. The waterline is shown as 600. The buoyancy of the hatches can raise the crane so it can be moved from anywhere on the vessel.

A preferred moveable crane lifting system is shown in FIG 25 wherein the crane (430) has a base (432) , midsection (434) and top (436) . This crane can be a modular crane with the segments connected together or it can be a one-piece unit, preassembled on land prior to installation on the catamaran.

A first buoyant hatch (438) is secured to the base of the crane with two attachment devices, (446) and (448) . A second buoyant hatch (440) is secured to the midsection using a third and fourth attachment device (444), and (450) on the opposite side from the first hatch.

The first hatch and the second hatch are secured to the base at a point such that when the catamaran is submerged, the crane floats slightly from the support surface (12) and the crane is movable around the catamaran support surface.

The man skilled in the art will appreciate that the floatable displacement of the crane over the support surface also can be applied to the gantry described earlier.

As will be apparent from the description the fifth aspect of the present invention relates to a method for operating a catamaran adapted for lifting loads, wherein said catamaran comprises a bow and a stern; a first submersible float; a second submersible float, wherein said second submersible float is disposed in a parallel relation to said first submersible float; a support surface forming a top to said first and second submersible floats and a slot opening disposed between the first and second submersible floats; a first load supporting movable column disposed on said solid support surface having a first motion compensator system with winch; a second load supporting movable column disposed on said solid support surface having a second motion compensator system with winch; a first ballast system disposed in said first submersible float; a second ballast system disposed in said second submersible float, and a hatch disposed in said support surface; wherein said method comprises: disposing the hatch on top of and between said first and second load supporting moveable columns; placing a first sheave on one end of said hatch and a second sheave on the other end of said hatch wherein the first and second sheaves are located in close proximity to the edge of said first and second load supporting moveable columns; a third sheave disposed on the top of said first load supporting moveable column, and a fourth sheave disposed on the top of said second load supporting moveable column; connecting a first lifting line from a first motion compensator with winch contained in said first load supporting moveable column running it over said first and second sheave and engaging one side of a load, and connecting a second lifting line from a second motion compensator system with winch contained in said second load supporting moveable column by running said second line over said second and fourth sheave and engaging with said load; and using the winches of said motion compensator system to lift the load.

Claims

C L A I M S

1. A method for erecting an object, in particular a lifting frame, comprising the steps of:

- providing a floatable object having a base and a top;

- providing a submersible vessel;

- placing the floatable object on the vessel,

- transporting the vessel with floatable object to a desired location;

- ballasting the vessel to permit the floatable object to float;

- securing the base of the floatable object to the vessel;

- securing a hoist line between the floatable object and a winch on the vessel;

- winching the hoist line and thereby raising the floatable object top from the water while the base remains secured to the vessel.

2. Method according to claim 1, wherein the floatable object is a lifting frame.

3. Method according to claim 2, wherein the lifting frame is an A-frame.

4. Method according to claim 1, wherein the floatable object is an oil derrick.

5. Method according to any of claims 1-4, wherein the vessel is a catamaran.

6. Method according to one or more of the preceding claims, further comprising the step of leveling the vessel using a ballast system once the floatable object is erected.

7. Method according to one or more of the preceding claims, further comprising the step of providing one or more floating devices and securing the one or more floating devices to the object.

8. Method according to one or more of the preceding claims, wherein said vessel is moved while semi-submersed and while the object is upright.

9. Method according to one or more of the preceding claims, wherein said vessel is ballasted to a normal draft depth once the erectable object is upright on the vessel.

10. In combination a floatable object having a base and a top and a submersible vessel;

wherein said vessel allows for placing the floatable object on the vessel, so that the vessel with floatable object is transportable to a desired location and the vessel can be ballasted to effect floating of the floatable object;

and wherein coupling means are provided for securing the base of the floating object to the vessel;

wherein a winch and hoist line are provided on the vessel, so that the hoist line is attachable to the object and by winching the hoist line the floatable object top is raised from the water while the base remains secured to the vessel.

11. The combination of claim 10, wherein the floatable object is a lifting frame, preferably an A-frame.

12. The combination of claim 10 or 11, wherein said vessel is a catamaran comprising a first submersible float and a second submersible float disposed in a parallel spaced relation to said first submersible float, each submersible float having a float bow, a float midsection, a float tail and float stern, and wherein a first ballast system is associated with said first submersible float; a second ballast system is associated with said second submersible float, and wherein said first and second ballast systems are adapted to raise and lower said catamaran with respect to a waterline.

13. The combination of claim 12, wherein said catamaran has a support surface forming the top of said first and second submersible floats, which support surface is adapted for supporting heavy loads and an air gap is present between said first and second submersible floats and said support surface.

14. The combination of any of claims 12-13, wherein a slot opening is disposed between the tails of said first and second submersible floats.

15. The combination of any of claims 12-14, wherein a first and second load supporting movable column are disposed on said support surface.

16. The combination of any of claims 12-15, wherein a fixed column is disposed on a submersible float at the bow.

17. The combination of any of claims 12-16, wherein the catamaran comprises a securing system for securing the catamaran to another object, which securing system comprises: tensioning lines; a winch; a first motion compensator disposed in a first load supporting moveable column; a second motion compensator disposed in a second load supporting moveable column; and control means to enable said first and second motion compensators to tension.

18. A method for constructing a gantry at sea using a catamaran,

wherein the catamaran comprises : - first and second submersible floats disposed in parallel spaced relation to each other,

- a support surface forming the top of the first and second submersible floats,

- a first, second, third and fourth load supporting moveable columns disposed on the support surface,

- a first lifting mechanism between the first and second load supporting moveable columns, wherein said first lifting mechanism comprises a first plate and first and second winches for lifting the first plate, and - a second lifting mechanism between the third and fourth load supporting movable columns, wherein said second lifting mechanism comprises a second plate and third and fourth winches for lifting the second plate;

- at least one hatch;

wherein the method comprises the steps of:

- disposing a hatch between the first and second plates;

- fastening a hoist to the hatch forming a gantry top;

- lifting the gantry top using the first and second plates;

- fastening said gantry top to the top of said first, second, third and fourth load supporting moveable columns with first, second, third and fourth fasteners;

- lowering the first and second plates to the support surface forming first and second spaces between the plate and the gantry top ;

- disposing in the first space between the first and second load supporting movable columns on the first plate, a first gantry leg piece;

- disposing in the second space between the third and fourth load supporting moveable columns on the second plate a second gantry leg piece;

- lowering the gantry top onto the first and second gantry leg pieces and locking the first and second gantry leg pieces to the gantry top forming a first segment;

- lifting the first segment with the first and second plates and fastening the first segment to the top of said first, second, third and fourth load supporting moveable columns;

- lowering the first and second plates and creating again the first space and the second space;

- disposing in the first space a third gantry leg pieces and in the second space a fourth gantry leg piece;

- lowering the first segment down to the top of the third and fourth gantry leg pieces and locking the first segment to the third and fourth gantry leg pieces, forming a second segment;

- lifting the second segment with the first and second plates and locking the second segment to the first, second, third and fourth load supporting movable columns;

- lowering the first and second plates forming first and second spaces , and

- repeating the process until the gantry is built.

19. A catamaran including a gantry to be constructed according to the method of claim 18.

20. A method for installing a topsides consisting of:

a. placing a topsides onto a barge;

b. maneuvering the barge near a catamaran;

wherein the catamaran comprising a first submersible float and a second submersible float disposed in a parallel spaced relation to said first submersible float, each submersible float having a float bow, a float midsection, a float tail and float stern, wherein said catamaran has a support surface forming the top of said first and second submersible floats,

said catamaran further comprising a support surface forming the top of said first and second submersible floats, wherein said solid support surface is adapted for supporting heavy loads and wherein an air gap is present between said first and second submersible floats and said support surface and wherein a slot opening is present between the tails of said first and second submersible floats;

a first load supporting movable column being disposed on said support surface; a second load supporting movable column also being disposed on said support surface;

a first ballast system being associated with said first submersible float; a second ballast system being associated with said second submersible float, wherein said first and second ballast systems are adapted to raise and lower said catamaran with respect to the waterline; the catamaran comprising a securing system for securing the catamaran to another object, wherein the securing system comprises: (i) tensioning lines; (ii) a tensioner; (iii) a first motion compensation system disposed in said first load supporting moveable column connected; (ii) a second motion compensation system disposed in said second load supporting moveable column; and (iii) control means to enable said first and second motion compensation systems to tension;

c. submerging the catamaran using the ballasting system;

d. maneuvering the barge over the catamaran and between the first and second load supporting moveable columns;

e. damping the relative motion between barge and catamaran using the securing system and raising the catamaran enough to transfer load from the barge to the load supporting moveable columns;

f. lowering the barge using the securing system until it floats;

g. floating the barge away from the catamaran;

21. Method according to claim 20, wherein, once the catamaran has moved to an installation site, the method comprises the additional steps :

a. positioning the catamaran over the installation site;

b. damping the relative motion using the securing system and ballasting the catamaran to lower the topsides over the installation site;

c. transferring load to the installation site from the load supporting columns; and

d. moving the catamaran away from the installation site using a draft, which is deeper than a normal draft for the vessel.

22. A method for lifting and transporting a topsides with a catamaran, comprising the steps of:

a. placing the topsides on a wagon;

b. driving the topsides onto a barge;

c. maneuvering the barge to a position near a catamaran;

a first ballast system being associated with said first submersible float; a second ballast system being associated with said second submersible float, wherein said first and second ballast systems are adapted to raise and lower said catamaran with respect to the waterline;

the catamaran comprising a securing system for securing the catamaran to another object, wherein the securing system comprises: (i) tensioning lines; (ii) a tensioner; (iii) a first motion compensation system disposed in said first load supporting moveable column connected; (ii) a second motion compensation system disposed in said second load supporting moveable column; and (iii) control means to enable said first and second motion compensation systems to tension;

d. submerging the catamaran;

e . maneuvering the barge over the catamaran and between the first and second load supporting moveable columns,

f. raising the catamaran enough to transfer load from the barge to the load supporting moveable columns;

g. removing the barge;

23. Method according to claim 22, wherein, once the catamaran has moved to an installation site, the method comprises the additional steps :

a. positioning the catamaran over the installation site;

b. ballasting the catamaran to transfer the topsides onto the installation site; and

c. moving the catamaran away from the installation site using a draft which is deeper than a normal draft for the vessel.

24. Method according to any of claims 20-23, wherein the catamaran is used in a semi-submerged state to transport the topsides and minimize motions on the catamaran.

25. A method for installing a topsides to form an offshore platform, with the topside initially at a wharf and an intended installation at a location remote from the topside initially, the method comprising the steps of:

a. placing a topside on a transport wagon ;

b. rolling the transport wagon onto a barge and positioning the topsides on the barge wherein a portion of the topsides extends out over opposing sides of the barge; c. moving the barge to a catamaran comprising having a bow and a stern, a first submersible float; a second submersible float, wherein said second submersible float is disposed in a parallel spaced relation to said first submersible float; a support surface forming the top of said first and second submersible floats and comprising at least two floatable hatches, and wherein said hatches are adapted for supporting heavy loads and a slot opening is disposed between of said first and second submersible floats on one end;

the catamaran further comprising a first and a second load supporting movable columns and each load supporting moveable column having a winching system disposed on said first submersible float; a third and fourth load supporting movable column and each load supporting moveable column having a winching system disposed on said second submersible float;

the catamaran further comprising a first ballast system associated with said first submersible float, a second ballast system associated with said second submersible float, wherein said first and second ballast systems are adapted to raise and lower said catamaran with respect to the waterline;

the catamaran further comprising a horizontal positioning system comprising: at least three horizontal maneuvering winches at least three lines each connected on one end to a winch and on the other end to an object at sea and a controller for orienting the catamaran relative to said object at sea and wherein said controller monitors the tension on said at least three lines and said controller initiates winch pay out of lines when load on any one of said lines exceeds a first preset limit, and further said controller initiates winch tensioning of line when tension on any one of said lines falls below a second preset limit;

and a vertical securing system for securing the catamaran to another object further comprising: (i) a first line secured on one end substantially vertically to an object at sea, (ii) a second line secured on one end substantially vertically to said object at sea, (iii) a first motion compensator system disposed in said first load supporting moveable column connected to the other end of said first line; (iv) a second motion compensator system disposed in said second load supporting moveable column connected to the other end of said second line; and (v) a control system for monitoring and controlling tension between first and second motion compensators and said object at sea;

d. using one of said two floatable hatches to form a first base between said first and third load supporting movable columns and using the other of said two floatable hatches to form a second base between said second and third load supporting moveable columns , connecting said first base to the winching system of said first load supporting moveable column and said third load supporting moveable column, and connecting said second base to the winching systems of said second load supporting moveable column and said fourth load supporting moveable column;

e. lowering the catamaran below the water line;

f. maneuvering the barge over the first and second base;

g. raising said first and second base using said winching systems lifting the barge to synchronize the barge movements with the catamaran;

h. partially deballasting the catamaran raising it until the topsides on the transport wagon touch the top of the first, second, third and fourth load supporting moveable columns;

i. transferring load of the topsides from the barge to the catamaran;

j . lowering the first and second base thereby lowering the barge;

k. removing the barge from a position over the catamaran;

1. moving the catamaran to an intended installation; m. maneuvering the catamaran to that the intended installation is contained within the slot opening;

n. ballasting and lowering the catamaran in the water, until the topsides touch the supports of the intended installation;

o. transferring load from the catamaran to the intended installation.

26. Method of claim 25, further comprising the step of using at least two motion compensators to secure the catamaran to the intended installation prior to deballasting and lowering the catamaran with the topsides.

27. The method of claim 26, wherein the motion compensators comprise:

- a winch,

- at least one line connected to the winch and vertically connectable to an object in the water,

- a tension-measuring device connected to said line;

- a motion control device connected to said line and winch for monitoring and controlling tension on said line.

28. Method according to any of claims 23 - 26, further comprising using an element between said topsides and said load supporting moveable columns to dampen movement between the topsides and the catamaran, e.g. a rubber disc or an element of an elastomeric material .

29. Method according to any of claims 22 - 28, wherein further comprising using the step of between 4 and 16 tensioning lines connected to the motion compensators to synchronize the movements of the catamaran and the barge or installation site when lifting the topsides from a barge or lowering the topsides onto the installation site.

30. Method according to any of claims 27-29, wherein the intended installation site is a floating platform.

31. Method according to any of claims 27-29, wherein the intended installation site is a fixed leg platform.

32. Method according to any of claims 27-29, wherein said catamaran is operated at a depth selected from the group:

a normal draft, a slightly submerged draft, wherein water fills the air gap between the first and second submersible floats and the solid support surface is above the water level, and a lower draft, wherein between 1 and 20 meters of water covers the solid support surface.

33. Method according to any of claims 27-32, wherein the topsides extends beyond the hull of the catamaran.

34. A submersible vessel having a submersible vessel hull and a crane supported on said hull for lifting objects, wherein the crane is adapted to be floatable, such that when the hull of the vessel is submerged the crane floats with respect to the vessel hull and wherein the hull provides multiple crane positions for supporting the crane on the said hull, such that the floating crane is displaceable from one crane position to another crane position.

35. Vessel according to claim 34, wherein said vessel has one or- more associated buoyancy members releasably attachable the crane so that the crane is rendered floatable.

36. Vessel according to claim 35, wherein the vessel is a catamaran having spaced parallel floats and a support surface across the top of the floats and spanning the gap between the floats, wherein said support surface in the area of the gap is partly formed by a buoyant hatch, which is hatch is removable from the support surface and is adapted to be secured to said crane to render the crane floating.

37. Method for operating a catamaran adapted for lifting loads, wherein said catamaran comprises a bow and a stern; a first submersible float; a second submersible float, wherein said second submersible float is disposed in a parallel relation to said first submersible float; a support surface forming a top to said first and second submersible floats and a slot opening disposed between the first and second submersible floats; a first load supporting movable column disposed on said solid support surface having a first motion compensator system with winch; a second load supporting movable column disposed on said solid support surface having a second motion compensator system with winch; a first ballast system associated with said first submersible float; a second ballast system associated with said second submersible float, and a hatch disposed in said support surface; wherein said method comprises: disposing the hatch on top of and between said first and second load supporting moveable columns; placing a first sheave on one end of said hatch and a second sheave on the other end of said hatch wherein the first and second sheaves are located in close proximity to the edge of said first and second load supporting moveable columns; a third sheave disposed on the top of said first load supporting moveable column, and a fourth sheave disposed on the tope of said second load supporting moveable column; connecting a first lifting line from a first motion compensator with a winch contained in said first load supporting moveable column running it over said first and second sheave and engaging one side of a load, and connecting a second lifting line from a second motion compensator system with winch contained in said second load supporting moveable column by running said second line over said second and fourth sheave and engaging with said load; and using the winches of said motion compensator system to lift the load.