Abstract: A guidance system for centering and guiding various drill strings or risers within a moonpool of a floating structure, e.g. a caisson vessel. The system comprises one or more guidance vehicles. Each vehicle is movably mounted on a separate track. The tracks, in turn, are spaced about the moonpool wall and extend vertically along the wall of the moonpool from the top of the moonpool to a point near its bottom. Each vehicle has a frame and means to mount the frame on its respective track. Two side arms and a center arm are pivotably mounted on the frame and are movable between a closed position and an open position. Mounted at the outer end of each of the arms is an interchangeable workhead assembly which engages a drill string or riser to center and guide the drill string or riser when the arms are in their closed position. Individual lines controlled by winches above the moonpool are attached to each vehicle for independently raising and lowering that vehicle within the moonpool.

Abstract: The invention relates to an elongated buoyant arm mounted below the water line of a drilling vessel. The arm is of variable buoyancy and is attached to a drilling riser extending between the drilling vessel and the sea bottom to maintain tension on the riser.

Abstract: A method and apparatus is disclosed for a marine production riser system. The system includes a series of housing sections linked to form a vertical riser column. The integrity of the riser column is maintained by guidelines extending in tension between a subsea installation and a surface vessel. Each housing section has a plurality of passages extending therethrough. Fluid-handling lines retained within the passages are isolated from current forces by the housing sections. To utilize the invention, the nonbuoyant housing sections are positioned between the guidelines, are loosely banded to the guidelines, and are lowered to form the riser column. Fluid-handling lines are threaded through axially-coinciding passages located in each housing section and continuous throughout the riser column. The fluid-handling lines are connected at the sea floor and surface vessel to complete a fluid carrying system.

Abstract: A riser tensioner safety system for preventing damage to a floating drilling vessel in a broken cable event or an emergency disconnect of the riser is disclosed. The system uses standard pneumatic/hydraulic tensioning devices together with a safety valve which is installed in the hydraulic fluid supply line to the tensioning device. The valve is held open by tension in the riser tensioner lines. If tension drops below a predetermined level due to a broken cable event or an emergency disconnect of the riser, the valve closes rapidly preventing acceleration of the tensioner piston.