Function
Jewellery is the term used to describe a range of items that are attached to mooring lines either to connect sections of a line or items that may be connected along the length of the line.
What it costs*
About £8.6 million for a 450 MW floating offshore wind farm.
Who supplies them
Connectors: Hydrosphere, InterMoor, The Crosby Group and Vicinay Marine.
Clump weights: FMGC, Hydrosphere and InterMoor.
In-line tensioners: Delmar Vryhof, Macgregor, Flintstone Technology and Vicinay Marine.
Load reduction devices: Dublin Offshore, Intelligent Mooring, TfI Marine.
Mid-line buoyancy elements: Balmoral, DeepWater Buoyancy, InterMoor and SBT Energy.
Clump weights, buoyancy elements, load reduction device, and floating substructure and mooring line connector (clockwise from top left). Images courtesy of Hi-Sea Marine, Balmoral, Dublin Offshore and First Marine Solutions . All rights reserved.
Key facts
The major items include:
- Clump weights: these are masses, which can be several tonnes each, and are attached to mooring lines to tune the compliant response. They could be fitted to the mid or upper-section to resist substructure uplift, to the mid-section to form a multi-catenary shape or be added to the ground-section to convert vertical forces into horizontal forces at the anchor.
- H-links: used to join two sections of the mooring line together. This could be between dissimilar materials or the same material of a different size.
- In-line tensioners: this is a simpler alternative to a powered winch to adjust the tension in a mooring system which would sit on the sea bed for the life of the project. For example, Delmar Vryhof’s Stevadjuster is positioned in the mooring line close to one of the anchors and is adjusted using a vertical pull from a bollard. A complete three-line mooring system can be tensioned using a single tensioner on one leg.
- Load Reduction Devices: components within the load path that modify the mooring stiffness response to reduce mooring dynamic loads. By delivering engineered compliance, LRDs allow the mooring to be optimised for both cost and risk. LRDs come in a variety of forms including:
- Gravitational devices using weight and buoyancy (such as the Dublin Offshore LRD)
- Elastomeric devices using high-strain tensile materials (such as TFI Marine’s SeaSpring)
- Compressive devices using high-strain materials
- Compressive devices using hydraulic systems
- Mid-line buoyancy elements: these are flotation devices, which can provide several tonnes of uplift each, and are attached to mooring lines. Their function is either to lift the lower section of the mooring line above the sea bed to prevent damage or to fine tune the compliant response by forming a multi-catenary shape.
- Shackles: used to attach each end of the mooring line to the anchor and substructure, respectively.
- Swivels: used to stop twist in the mooring line.
- Tri-plates: flat plates with three holes, used to allow connection of two sections of mooring line with a clump weight or buoyancy element.
- Most of these items are expected to be catalogue items used in other marine industries, initially, but could become more specialised to floating offshore wind’s needs over time, particularly for volume and cost reduction.
What’s in it
- Clump weights (made from cast iron)
- In-line tensioners (made from fabricated steel with some forged components)
- Load reduction devices (expected to be made from steel fabrications, glass fibre components, synthetic materials and/or hydraulic elements, depending on the type and specific design)
- Mid-line buoyancy elements (made from synthetic materials)
- Shackles, H-links, and swivels (made from forged steel)