Submerged Turret Production

The Submerged Turret Production is a turret mooring system for FPSO vessels suitable for seas as high as 16 m Hs and water depths to 2600 m.


The Submerged Turret Production (STP™) is a unique, innovative, and flexible turret mooring system for floating production, storage, and offloading (FPSO) vessels, making it suitable for a wide range of applications. As a further development of the Submerged Turret Loading (STL™) system, STP is combined with a high-pressure multipath swivel to create a complete turret and swivel package.

STP or FPSO vessel mooring is developed from the basis of the proven STL system. The STP swivel mounted on top of the turret buoy transfers oil, water, gas, signals, and power from the geostationary riser system to the piping and cabling system of the freely weathervaning production vessel. 

As for STL, the STP system enables schedule decoupling between the offshore and shipyard work. The disconnect feature of the buoy simplifies unplanned repair, upgrading, inspections, and replacement of the FPSO vessel as well as abandonment of the field.

Permanent or disconnect mooring

As for STL, the STP system can be designed for disconnect service or for permanent mooring throughout the field life.

STP integration

The STP compartment in the FPSO vessel is a cylinder extending from the bottom to upper deck, with the receiving cone as the lower part. With a diameter of 10 to 18 m, the impact on the hull is minimal. Only local reinforcements of standard steel work are required. The turret integration into the FPSO vessel is simplified by bearing structures integrated in the STP buoy as opposed to bearings integrated with the FPSO vessel hull.

STP system references

STP systems in service cover a wide range of applications—from the harsh North Sea environment to cyclone-prone areas such as China or Australia, mooring caters for seas as high as 16 m Hs (significant wave height), water depths up to 2600 m, vessel sizes up to very large crude carriers, throughput up to 600,000 BOPD, etc.

STP in ice

Icebergs and ice ridges in Arctic environments are better addressed with the quick disconnect features provided by the STP system. STP systems are verified in ice environments, and model tests have documented survival of a vessel moored in 1.6 m-level ice with a drift speed of 0.75 m/s.


  • A buoy moored to the seabed is pulled into and secured in a mating cone in the vessel.
  • The buoy incorporates a turret connected to the mooring and the riser(s).
  • All STLs are based on standardized mating cone geometry in the vessel.
  • APL Mooring and Loading Systems Brochure

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