Mooring systems play a crucial role in the offshore industry by ensuring the stability and safety of floating structures under various environmental conditions. These systems are designed to restrict the horizontal movements of the structure caused by external forces like wind, currents, and waves. By limiting these excursions, mooring systems help maintain the position and integrity of offshore installations such as floating production platforms, drilling rigs, and floating wind turbines.
One commonly employed mooring system is the external turret system. In this configuration, the turret assembly is positioned outside the vessel, allowing it to rotate freely according to the prevailing environmental load direction. This rotational capability is known as “weathervaning.” By aligning itself with the dominant forces, the turret system minimizes the loads exerted on the mooring lines, enhancing the overall stability of the floating structure.
The external turret system typically consists of a buoyant turret structure located near the waterline, which is connected to the vessel through a swivel mechanism. The swivel enables the transfer of fluids, such as oil or gas, between the floating structure and the seabed without entangling or damaging the mooring lines. Additionally, the turret may house essential equipment, such as risers, which connect the structure to subsea wells or pipelines.
The mooring lines in an external turret system are typically a combination of chains, wires, or synthetic ropes. These lines are anchored to the seabed or pre-installed mooring anchors and are connected to the turret structure. The tension in the mooring lines acts against the environmental loads, preventing excessive movements of the floating structure. The number and arrangement of mooring lines depend on factors such as the size of the structure, environmental conditions, and required holding capacity.
By allowing weathervaning and reducing the loads in the mooring lines, the external turret system offers several advantages. It improves the dynamic response of the floating structure, increasing its ability to withstand extreme weather conditions such as storms and hurricanes. The turret’s rotation allows the structure to align itself with the wind, current, and wave forces, reducing the hydrodynamic forces acting on the hull. This design flexibility makes the external turret system suitable for various offshore applications, including deepwater oil and gas production, floating liquefied natural gas (FLNG) facilities, and offshore wind farms.
In summary, mooring systems, such as the external turret system, are vital components of offshore installations. They ensure the stability and integrity of floating structures by limiting horizontal movements caused by environmental loads. The external turret system, with its weathervaning capability and reduced mooring line loads, offers enhanced safety and performance, making it a preferred choice in many offshore applications.