Submerged Turret Production / Loading buoy mooring is different from mooring Spars, Floating Production Units and FPSOs. During submerged turret buoy installation, the buoy is moored subsea and then raised into the FPSO. It may also at some point need to be lowered from the FPSO due to vessel replacement / upgrades and during extreme weather conditions.
For an STP / STL buoy mooring, the Ballgrab female receptacles are instead pre-installed on the buoy's underside with a uni-joint arrangement. Once positioned in the field, all the male Ballgrab tools, linked by chain / rope to the sea bed, are connected by ROV to the female receptacles attached to the buoy.
Typically the mooring line features a Midline Buoyancy Element (MLBE) which is used to hold the line above the sea bed and provide the mooring line 'slack' necessary to accommodate the movement of the buoy from its subsea position say, 70m below the surface into the FPSO.
Benefits of Ballgrab submerged turret buoy mooring include:
• Avoids the need for divers, and is a safer connection technique than traditional surface connection methods.
• Absence of wires connected to the underside of the buoy allows the buoy to be lifted into the water in a far simpler way, without the need for numerous cranes to support the wires as the buoy is lifted.
• Simpler STP / STL buoy as pre-installing the female receptacles on the buoy mean it can be towed to the field with no mooring wires connected and hence requires fewer vessels in the tow-out fleet.