Abstract: A method and vessel for removing or installing an offshore jacket structure in a body of water, the vessel having a generally planar main buoyancy section having the outline of a delta with an extension at the apex and auxiliary buoyancy sections extending transversely of the main buoyancy section at the ends of the base of the delta. The bottom parts of the auxiliary buoyancy sections have a rounded outer surface and contain heavy fixed ballast. The vessel may be rotated as it is brought close to the jacket structure with the auxiliary sections straddling the jacket structure. The vessel is rotated towards the jacket structure while its rounded bottom portion rolls on the seabed. Once the jacket structure is connected securely to the vessel, the vessel is rotated back to the initial position de-ballasting the auxiliary sections before it is brought to the surface.

Abstract: A method for removing or installing an offshore jacket structure (15) in a body of water utilises a vessel (1) having a generally planar main buoyancy section (2) having in plan view substantially the outline of a delta with an extension (4, 5) at the apex and auxiliary buoyancy sections (3, 8) extending transversely of the main buoyancy section at the ends of the base of the delta. The bottom parts (8) of the auxiliary buoyancy sections (3) are pro-vided with a rounded outer surface (11) and contain heavy fixed ballast (12). By suitable ballasting the vessel (1) may be rotated so that the main section (2) forms an angle less than 90 degrees with the water surface (17) as it is brought close to the jacket structure with the auxiliary sections (3) straddling the jacket structure.