The articulated column semi-submersible platform concept was developed to provide the offshore industry with a stable working platform which is effective over. a wide range of sea conditions. The platform design emphasizes safety, stability, and mobility. Major parts are a moveable upper hull, a submerged lower hull, and multiple articulated column stabilizers which are connected to the periphery of the lower hull. The lower hull is configured as a barge and transits are made with this hull on the surface. On station the hull is submerged and the upper hull becomes the working platform Which is maintained clear of the water surface. Articulated column stabilizers minimize the motion response of the rig.
The platform is applicable to any situation where a stable working base is required in the open §ea. Particular applications include exploratory drilling, offshore oil storage, and an offshore research station.
The semi-submersible ocean platforms which have appeared in ever increasing numbers in recent years not only as offshore drilling rigs function on the concept of their being transparent to the motion of the sea. This is to say that the designer attempts to make the platform as motionless as possible while remaining within stringent operational and economic boundaries. Operational considerations take on a variety of forms. A partial listing includes water depth, payload, weather and sea conditions, mobility, transit speed, mooring or positioning systems, and motion response. Economic factors are directly related to the initial cost, maintenance requirements, casualty insurance costs, and most important of all, the ability to the platform to perform its assigned task. These considerations led to the development of the articulated column semisubmersible stable ocean platform. The sections that follow discuss the concepts involved and the development work on the rig.
The fundamental concept underlying a semi-submersible rig is the achievement of stability through the use Ef a vertical column or spar type buoy. The column, when compared with a conventional surface hull form, is characterized as having a deep draft, small water plane area, and a relatively modest payload capability. Certain of these factors are particularly desirable, i.e., the deep draft and small water plane area minimize motion response at conditions other than resonance. Certain other factors are undesirable: the deep draft limits the areas where it can be used; small water plane area limits the payload capability of the platform; and at conditions at or near resonance, the motion of an un damped column can become very large.
