A method for installation of an elongate element in a stretch of water, the method including reversible fastening of a connecting member (34) at a first end (16) of the elongate element (10); arranging the elongate element (10) in a substantially horizontal configuration; reversibly engaging the connecting member (34) in a retaining member (36); pivoting the elongate element (10) about a substantially horizontal axis to move the elongate element (10) into a substantially vertical configuration, while the connecting member (34) remains engaged in the retaining member (36); joint lowering of the retaining member (36), the connecting member (34) and the elongate element (10) in the stretch of water (12) with the help of a lowering line (152); detaching the connecting member (34) of the first end (16) of the elongate element (10), and joint raising of the retaining member (36) and the connecting member (34).

An offshore structure comprises a hull having a longitudinal axis, a first end, and a second end opposite the first end. In addition, the structure comprises an anchor coupled to the lower end of the hull and configured to secure the hull to the sea floor. The anchor has an aspect ratio less than 3:1. The hull includes a variable ballast chamber positioned axially between the first end and the second end of the hull and a first buoyant chamber positioned between the variable ballast chamber and the first end of the hull. The first buoyant chamber is filled with a gas and sealed from the surrounding environment. Further, the structure comprises a ballast control conduit in fluid communication with the variable ballast chamber and configured to supply a gas to the variable ballast chamber. The structure also comprises a topside mounted to the first end of the hull.

The offshore jack-up has a hull and a plurality of moveable legs engageable with the seafloor. The offshore jack-up is arranged to move the legs with respect to the hull to position the hull out of the water. The method comprises moving at least a portion of a vessel underneath the hull of the offshore jack-up or within a cut-out of the hull when the hull is positioned out of the water and the legs engage the seafloor. A stabilizing mechanism mounted on the jack-up is engaged against the vessel. The stabilizing mechanism is pushed down on the vessel to increase the buoyant force acting on the vessel.

The invention relates to a method for the installation of a marine (or in general, aquatic) wind-powered generator tower, wherein said tower advantageously comprises a foundation that is open at the top and equipped with a substantially flat lower slab and a perimeter wall. The method includes, in the different stages thereof, the depositing or removal of ballast material in or from the main cavity of the foundation, and wherein in the absence of said ballast material, the wind-powered generator or the foundation is a floating or self-floating structure. The method is particularly suitable for the installation of wind-powered generators in areas of low depth (or near-shore areas), preferably of less than 15 m.

A jack-up platform is described having a horizontal working deck that may be jacked up out of the water by moving its legs to a position wherein they take support on an underwater bottom. The jack-up platform further includes a higher level deck and a lower level deck that define a receiving space for a barge, optionally suitable for carrying parts for construction of a wind turbine, and further a deballasting system configured to bring the floating hull between a receiving position at which the hull is ballasted to a receiving draft in which the lower level deck is submerged underwater and the barge may be received in the receiving space through an opening in the hull, and an operational smaller draft where substantially no water can flow on either of the lower and higher level decks. The receiving space has a centralizing system configured to substantially centralize the received floating barge in the receiving space. A method for facilitating the offshore installation of a wind turbine using the jack-up platform is also described.

The offshore jack-up has a hull and a plurality of moveable legs engageable with the seafloor. The offshore jack-up is arranged to move the legs with respect to the hull to position the hull out of the water. The method comprises securing the vessel with respect to the hull of the offshore jack-up when the hull is positioned out of the water and the legs engage the seafloor. A lifting mechanism mounted on the offshore jack-up engages with a cargo carrying platform positioned on the vessel. The platform is lifted with the lifting mechanism between a first position on the vessel and a second position clear of the vessel.

An offshore structure for drilling and/or producing a subsea well includes a hull having a longitudinal axis, a first end, and a second end opposite the first end. The hull includes a plurality of parallel elongate columns coupled together. Each column includes a variable ballast chamber positioned axially between the first end and the second end of the hull and a first buoyant chamber positioned between the variable ballast chamber and the first end of the hull. The first buoyant chamber is filled with a gas and sealed from the surrounding environment. The offshore structure also includes an anchor fixably coupled to the second end of the hull and configured to secure the hull to the sea floor. The anchor has an arrow-shaped geometry and a central axis coaxially aligned with the longitudinal axis of the hull. The anchor includes angularly-spaced penetration members extending radially from the central axis of the anchor. In addition, the offshore structure includes a topside mounted to the first end of the hull.

An installation arrangement with a barge and a jack-up rig which floats in a first position on the sea and has a hull which is slotted vertically from the surface of the sea and has a slot width which is greater than that of the barge so that the barge can move into a slot, wherein the jack-up rig has supporting legs which can move to and from along a height relative to the hull and can be set down on the seabed. The hull and the barge can be lifted along the support legs. The slot extends along the entire longitudinal extent of the barge over the entire height of the hull, and securing means are arranged on the barge and on the slot and said securing means interact and secure the barge in the raised position in a fixed position on the jack-up rig.

A precast concrete gravity-base foundation is provided that is both floatable and submersible in water, and is suitable for mounting the shaft of an offshore wind turbine. The foundation comprises a bottom slab, four cylinders positioned at each corner, a centrally located cylinder, and a top slab covering each of the corner cylinders and having a central opening that receives the top portion of the centrally located cylinder. The foundation's configuration and positioning of the corner cylinders provide maximum stability, and once the corner cylinders are filled with sand, stone, or the like, the corner cylinders further bolster the overall mass and stability of the foundation. The foundation is produced on land, rolled onto a submersible jack-up barge, and transported to either a predetermined storage location or an installation site. The foundation's buoyancy and versatile storage options allow contractors to work year-round with fewer ships, cranes, equipment, and workers at the job site, making it a valuable addition to the offshore wind industry.

System for transporting an offshore structure, the system comprising: a transport apparatus, in particular a vessel or a vehicle, which is configured to receive an offshore structure and to form a slip joint with a slip joint section of a received offshore structure, wherein the system is configured to enter a releasable state, from a fixing state, wherein, in the releasable state, the slip joint formed by the transport apparatus and the offshore structure is smaller than that force in the fixing state.