Abstract:
A buoyant vessel which alone can support a heavy superstructure has a well within which a floating body is disposed. The floating body can displace sufficient water in the well to support the superstructure by itself. Valves are provided for transferring water into and out of the body to lower and raise the superstructure with respect to the water surface on which the vessel is floating.

Description:
This application is a continuation, of application Ser. No. 140,619, filed Jan. 4, 1988 now abandoned. 
    
    
     When a vessel element which holds a superstructure element at a small height difference above a fixed construction moves up and down as a result of wave movement, there is a great danger that the superstructure element will strike against the fixed construction with one or more violent impacts, such that the manoeuvre causes expensive damage to the fixed construction and/or the superstructure element. This danger of damage is markedly decreased if, during manoeuvering, the superstructure element is carried by at least one floater body that is held in at least one liquid bath carried by the vessel element. As a result, a loose vertical coupling can be realized during the first vertical contact between superstructure element and fixed construction. 
     If at least one refitted ship of large load capacity is employed as the vessel element, the vertical, reciprocating rolling movement is small, which reduces the problem considerably. This method can in addition be performed with a comparatively small investment, when supertankers surplus to requirements are available. 
     The invention can be used for the placing of a superstructure element as well as for its removal. It is also of importance that a superstructure element that may have been incorrectly placed on the fixed construction can again be removed in order to repeat the manoeuvre. 
     The invention also relates to and provides an installation for performing the inventive method, as well as a method for constructing a building structure in water and a thus-formed building structure. 
     During lowering of the superstructure element onto the fixed construction the liquid surface area is enlarged in order to limit the vertical movement of the floater body as a result of swell. The vertical movement that still occurs can be compensated for by swell compensators. The vertical movement to be compensated for by the swell compensators is preferably limited still further. 
     By using a part of the floater body for enlarging the water surface area, as a result of the loading thereof the weight of the floater body is increased so that the effect of enlarging the water surface area and increasing the weight of the floater body is combined. The floater body will therefore want to follow the movements of the vessel only to a very limited extent, which can be compensated for by swell compensators. 
     When the legs make contact with the pile heads, overflow valves to the floater bodies are opened at the same time. The liquid surface of the liquid baths then falls virtually immediately to the level of the overflow edge. As a result of the water flowing into the floater body, its weight is increased additionally and the load of the superstructure element on the pile heads increases rapidly. A wave surge that may occur no longer has any effect therefore on the position of the superstructure element. 
     The invention will be elucidated in the description following hereinafter with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings in schematic form: 
     FIG. 1 shows a broken away, perspective view of a preferred embodiment of an installation as according to the invention with which a superstructure element is transported to a fixed construction arranged in water; 
     FIGS. 2-5 show partly schematic cross sections along plane II--II of the installation in successive later stages during performing of the method according to the invention when the superstructure element is lowered onto a fixed construction; 
     FIG. 6 is a cross section corresponding with FIG. 2 of the installation during raising of the superstructure element from the fixed construction; 
     FIG. 7 shows the detail VII from FIG. 1 adapted into a preferred embodiment; and 
     FIGS. 8 and 9 are schematic examples of other installations for placing other superstructure elements on other fixed constructions. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A fixed construction 3 shown in FIGS. 1-7 consists of a tower anchored to the sea-bottom. Placed hereon is a superstructure element 2 which is prefabricated on shore and has a weight in the order of magnitude of 10,000 tons or more, for example 30,000 to 40,000 tons. Great problems occur with such heavy objects in controlling their horizontal and vertical movements, particularly during wave surge. An example of a construction is a building structure which forms an artificial island and which is used for surveying of the sea-bottom and/or extracting oil and/or gas. 
     The installation 1 comprises two vessel elements 4, namely two identical tanker ships of large dimensions, for example 100,000 tons, and preferably 300,000 tons each, so-called very large crude carriers, with a length of 340 m, a width of 53 m and a deck height of 28 m relative to the ship bottom. Such tankers are laid up and available at scrap prices. 
     The rear ends of vessel elements 4 are connected parallel to each other by means of bridge members 5. On their front ends, that is, on their sides facing each other, the vessel elements 4 have been given a recess 6 such that their distance from each other a at that point is greater than the mutual distance b at the rear ends. 
     Of importance is that, at least at the front end, there is sufficient distance present between them to accommodate the fixed construction 3. The recesses 6 have the advantage that the bearing width c of superstructure element 2 on vessel elements 4 is thereby reduced and the bridging members become simpler. It is equally conceivable that such recesses 6 are not applied. The rear end, that is the driving and accommodation of the tankers, is preserved. Cargo holds of the tankers are converted into liquid baths 7 in which are arranged floater bodies 8. The latter consist of tanks with a large volume such that their buoyancy can together support the weight of the superstructure element 2 and the girder bridges 9 when they are floating in the water 10 present in the liquid baths. Girder bridges 9 are supported on floater bodies 8 and are secured during transport by securing means (not shown). Floater bodies 8 have feet 12 with which they stand fixed on the bottoms 13 of liquid baths 7 during the transport of superstructure element 2 to fixed construction 3. 
     Having arrived at the fixed construction 3 the vessel elements 4 are ballasted by allowing surrounding outside water into various tanks. The liquid baths 7 are in any case filled with water, whereby the empty floater bodies 8 float upward. There is then a difference in height f of for instance 4 m between legs 27 of the superstructure element 2 and the corresponding pile heads 28 of fixed construction 3. In this situation the vessel elements 4 are navigated to either side of the fixed construction 3 (see FIG. 2). Use may hereby be made of anchor cables and or the propeller screws (not shown) of vessel elements 4. The floater bodies 8 are also carried by means of per se known swell compensators 15 which are controlled subject to the movements of vessel elements 4 and which comprise carrying ropes 16 guided repeatedly around pulleys 17 and hydropneumatic cylinders 18. It is noted that superstructure element 2, together with the girders 9 connected thereto and the floater bodies in turn connected to girders 9, form a stable vessel for floating on water. 
     When vessel elements 4 are situated roughly in position on either side of the fixed construction, non-actuated, horizontal hydropneumatic cylinders 20 already connected beforehand for pivoting on the fixed construction 3 are coupled for pivoting to projections 21 of superstructure element 2. Hydropneumatic holding cylinders 24, which support via rolls 25 against vertical end faces of girders 9, are actuated in order to hold superstructure element 2 in position in a horizontal direction relative to installation 1, while these cylinders 24 permit a relative vertical movement of the superstructure element 2 together with girders 9 and floater bodies 8. 
     Also present in lengthwise direction of vessel elements 4 are horizontal cylinders corresponding with cylinders 24 and 20. Using per se known measuring means (not described and not shown) the position of the legs 27 relative to the corresponding heads 28 of fixed construction 3 is measured, the one being arranged exactly above the other by regulating adjustment in opposing directions of pairs of cylinders 24 disposed opposite each other which still hold superstructure element 2 fixed in position between them. By regulating a pair of cylinders 24 arranged at the front end in opposing sense relative to a pair of cylinders 24 arranged at the rear end, the horizontal rotation can be controlled. 
     In this situation the superstructure element 2 is lowered to a small height difference g above fixed construction 3 by opening bottom valves 30 of floater bodies 8 so that water 10 flows out of liquid baths 7 into floater bodies 8, until the difference in height g (FIG. 3) amounts for example to just 2 m. Bottom valves 30 are then closed again. The spring rigidity of the hydropneumatic cylinders 24 is then simultaneously decreased and the spring rigidity of the hydropneumatic cylinders 20 is increased. In order to minimize the forces exerted by the superstructure element via the cylinders 20 on the fixed construction 3, the pressures of cylinders 20 are measured and cylinders 24 are actively actuated in selective manner as required. When superstructure element 2 is no longer moving in a horizontal direction relative to fixed construction 3, the superstructure element 2 is lowered onto fixed construction 3 by re-opening bottom valves 30. During this lowering, shut-off valves 31 on the upper part of liquid baths 8 are also opened, which results in additional liquid baths 33, located at a higher level, being filled with water from liquid baths 7. Created as a result is a large liquid surface area 34 (FIG. 4) common to liquid baths 7 and the associated additional liquid baths 33, as a result of which the vertical movement of floater bodies 8 causes the liquid surface area 34 to rise and fall to a lesser extent, so that the variation in the upward force is small. In other words, the vertical coupling between installation 1 and superstructure element 2 consequently becomes looser. Swell compensators 15 are in the meantime controlled such that vertical movements of vessel elements 4 are compensated. As soon as legs 27 make contact with the pile heads 28, overflow valves 89 to the floater bodies 8 are simultaneously opened, valves 31 81 are closed, and the lifting force of swell compensators 15 is virtually entirely eliminated. The liquid surface 34 of liquid baths 7 then falls almost immediately to the overflow brim 88 (see FIG. 5) so that the buoyancy of floater bodies 8 decreases in large degree, as a result of which the load transfer of the superstructure element 2 onto the pile heads 28 increases correspondingly rapidly. In the meantime water 10 is still flowing out of liquid baths 7 into floater bodies 8, resulting in the buoyancy of the floater bodies 8 decreasing still further. If meanwhile as a result of the upward swell movement of vessel elements 4 the floater bodies 8 are immersed slightly deeper into the liquid baths 7, more extra water may flow over the overflow brim 88 into floater bodies 8. Even if the floater bodies 8 were to be immersed further into the liquid 10 of liquid baths 7, the buoyancy would still never increase to the extent that superstructure element 2 is again lifted from pile heads 28. The increase in buoyancy is in any event limited by the level of the overflow brim 88. When the liquid level in and outside floater bodies 8 is equal, the upward force is zero, which means that the weight of the superstructure element 2 is fully supported by pile heads 28. 
     When it has been established that superstructure element 2 is standing in correct position on fixed construction 3, bridge girders 9 are released by disconnecting quick action couplings (not drawn) between girders 9 and floater bodies 8, the vessel elements 4 are further ballasted with water and the deep-lying installation 1 is removed backwards from fixed construction 3, leaving girders 9 behind. 
     If it should be the case that the superstructure element 2 is placed incorrectly on fixed construction 3, it can again be lifted up using installation 1 with small--that is, virtually without--risk of damage. The installation 1 comprises for this purpose storage tanks 43 disposed at a high level, each of which connects via channel 44 onto liquid baths 7. When lifting takes place, the following procedure is employed, starting from a situation where the installation 1 is located in position around fixed construction 3 and the vessel elements 4 are lying deep in the water, whereby the horizontal anchoring of installation 1 to superstructure element 2 is still very loose, that is, the cylinders 24 are not actuated. All the water is then first discharged from floater bodies 8 via hoses 46 and valves 47 to be opened, with bottom valves 30 remaining closed. This water then flows into ballast holds 48. 
     Water is subsequently pumped out of the ballast holds 48 in order to cause the vessel elements 4 to rise, in so far as this is necessary. When a small difference in level has been reached between superstructure element 2 and fixed construction 3, slide hatches 49 of storage tanks 43 are opened simultaneously so that the storage water runs via channels 44 into liquid baths 7, while valves 89 are closed. Care is also taken that during the period of release of superstructure element 2 from fixed construction 3 a large liquid surface area is present, by making use of the additional liquid baths 83, valves 81 being open. In the meantime the swell compensators 15 are utilized. When superstructure element 2 has been lifted sufficiently high, it can again be re-positioned. The spring rigidity of the cylinders 20 is reduced and that of cylinders 24 increased if the superstructure element 2 has to be removed. 
     As in FIG. 7, support means 50 are preferably arranged between the floater bodies 8 and superstructure element 2, these means consisting of removable columns 51 which grip with ball and socket joints 52 at low level on floater bodies 8, or at least at a low level such that these floater bodies 8 lie stable in the liquid baths 7. A plurality of liquid baths 7 with associated floater bodies 8 can be arranged in each vessel element 4. The existing transport reservoirs of tankers can thus be used as liquid baths 7 without a great deal of refitting. 
     The floater bodies 8 preferably have horizontal passages 53 to allow water to flow easily from one side of the floater bodies 8 to the other. Horizontal supports 54 can moreover be fitted through the bodies 8 for support of the bath walls where necessary. Instead of cylinders 20 and 24, winch cables can also be employed, whereby the tensile stress of the cables is adapted for altering in reverse sense the rigidity of the horizontal coupling between superstructure element 2 and fixed construction 3 on the one hand and of the coupling between superstructure element 2 and installation 1 on the other. 
     FIG. 8 shows that the installation 1 or at least an installation 61 similar to it can be very usefully employed for removing a superstructure element 2 from fixed constructions 3 as well as for sinking a superstructure or tunnel element 62 down onto a foundation 63. Ships that have sunk can also be raised according to this method. 
     It is remarked that instead of two vessels linked together by means of bridging members, the installation can comprise a single U-shaped vessel, the legs of this U forming vessel elements. Instead of the converted large tankets considered preferable, two assembled vessel elements may also be used that are provided with substantial ballast tanks, so that the level of these vessel elements can be adapted considerably relative to the surrounding outside water surface. 
     It is noted that in order to compensate a rolling movement of installation 1 the liquid baths 7 in both vessel elements 4 could be communicating. The bridge girders 9 are for example detached later from the superstructure element 2 and removed if they do not at least form part of the construction of superstructure element 2. 
     As seen in FIG. 9 a bridge 75 is being built, whereby a superstructure element 72 is placed on the fixed construction 73 using an installation 71 by means of a single vessel element 74 navigated between the bridge pillars 80. Vessel element 74 has liquid baths 77 in which are held floater bodies 78 which bear the superstructure element 72. The lowering of superstructure element 72 onto pillars 80 is in principle carried out further in the same manner as is described with reference to the FIGS. 1-6.