Single-Point Moorings

A single point mooring (SPM) is a floating buoy anchored offshore that allows the handling of liquid cargo in areas where a dedicated onshore facility for loading and unloading cargo is not available. They serve as a link between shore-based facilities and large oil tankers for loading or offloading oil and gas cargo. The SPM buoy is moored to the seabed using a mooring arrangement that it permits the buoy to move freely within defined limits that take into consideration waves, current and wind conditions.

The incorporation of a single point mooring monitoring system provides protection to the mooring by ensuring it is not overloaded. This allows for safe transfer of product and reduces the risk of accidents and expensive unscheduled down-time. This is particularly critical during product transfer operations due to the increased risk of spillage. There are more than 150 FPSOs (not counting FSOs) deployed in various parts of the world, including the North Sea, Offshore West Africa, Offshore Brazil, the South China Sea, and the Gulf of Thailand. Most of them use SPM systems for station-keeping.

We at TecRadon design Single-point mooring (SPM) systems to accommodate deep-draft tankers while they transfer crude oil and fuel oil to and from shore. The weathervaning capability of the SPM system reduces the loads due to wind, waves, and current, so that the dimensions of the mooring lines are effectively minimized. Our SPM systems for FPSOs have great adaptability to work in different environmental conditions despite them being technically challenging and expensive to build. The mooring system (the lines and anchor points) is always specifically designed to match the vessel’s requirements and local environmental conditions.

The mooring system is combined with a fluid transfer system that enables connection of (subsea) pipelines to the tanker. The fluid transfer system includes submarine hoses between the pipeline end manifold (PLEM) at the seabed and the buoy, and hoses between the buoy and the tanker. In the buoy a swivel provides the fluid transfer path between the geostatic part and the rotating part of the buoy. The type of bearing used and the split between the rotating and geostatic parts determine the concept of the buoy.