Abstract: A marine riser system is connected through flowlines and a moonpool plug assembly to a marine vessel. The moonpool plug assembly, when removed from the marine vessel, maintains a fully submerged position due to its having a buoyancy which is less than the net weight of the flowlines to which it is connected.

Abstract: A rotary transfer subsystem is described for transferring production fluids, electrical power, hydraulic power, and control signals across a rotating interface between an offshore process vessel and a flowline bundle of service hoses and high-pressure hoses which are connected to a deepwater production riser system. Tensioning devices are also described for maintaining a selected tension on terminal hoses between the interface and the vessel while the vessel weathervanes during maintenance of position in a watch circle above the riser system. The subsystem and the tensioning devices are mounted on the vessel which is equipped with a powered turret within a circular moonpool and is capable of performing most subsea service functions on the riser system without major equipment support.

Abstract: A marine compliant riser system connects a subsea hydrocarbon source to a floating surface facility through a lower multi-conduit riser section to a submerged buoy section located below a turbulent water zone and a flexible flowline. Fluid connection is established between corresponding lower riser conduits and the surface facility by a plurality of flexible conduits. Connection assembly means connects individual upwardly-directed flexible conduits with corresponding upwardly-directed lower riser conduits in fluid flow relationship. A yoke assembly mounted on the buoy section, includes beam means for holding a plurality of spaced apart flexible conduit terminations, with each of the flexible conduits being connected individually in catenary arrangement between the yoke assembly and the surface facility. The flexible conduits are attached to the surface facility in compact, non-linear array and to the yoke assembly in substantially linear array.