OFFSHORE VESSELS FOR SUPPORTING STRUCTURES TO BE PLACED ON OR REMOVED FROM THE SEABED OR OFFSHORE INSTALLATIONS

摘要

The disclosure relates to a vessel for installing or removing a structure at or from an offshore site, the vessel (21a,21b) being U-shaped in plan to provide an open-ended well to enable the vessel to be manoeuvred into position around an offshore site (22), and a plurality of lifting devices on the vessel for supporting/raising/lowering the structure for placement at or removal from the offshore site. Each lifting device comprises a tower (30) mounted on the U-shaped vessel, a hoist (60,61,62) on each tower for supporting the offshore structure and variable water ballast means (60,61) providing a counterweight for each hoist for operating the hoists to raise, hold in equilibrium or lower the structure.