Floating offshore wind uses floating platforms anchored to the seabed, enabling deployment in deeper waters where fixed-bottom turbines are not feasible, thus accessing stronger and more consistent wind resources.
This presents a mooring and anchoring challenge.
The ideal mooring solution depends on a range of factors including turbine foundation design, metocean conditions, water depth and seabed characteristics. For example, while stronger or more consistent winds might be favourable for power generation, an offshore installation exploiting them would subsequently have to withstand greater forces. Also, as more installations are deployed and prime sites are developed, it may be necessary to install windfarms in areas with difficult ground conditions.
A FLOW (floating offshore wind) farm might require hundreds of anchors, because each turbine often needs multiple anchors to withstand 1 in 50 or 1 in 100 year storms and to comply with the requirements of insurance providers.
In addition, the mooring technology must be economically viable at scale, deployable rapidly and able to withstand the loads of the mooring lines for the project’s lifetime.
The industry’s traditional solutions, such as drag embedment, suction pile or driven pile anchors, have predominantly been developed in the oil and gas market, where risks and requirements differ. Consequently, they can be suboptimal choices for floating offshore wind.
Enter JAVELIN
JAVELIN is a slender, deep embedment anchoring solution suitable for a range of geologies, water depths and design loads. Developed by offshore crew and cargo transfer specialist, Reflex Marine, the JAVELIN Lower Anchor (JLA) accesses the more competent strata found at greater depths in the seabed. The JLA can be locked in place with either a conventional cement grout bond or a novel aggregate locking system, which grips the sediment in a similar way to a wall-plug.
“The shape of the components and novel locking mechanism of the JLA generates hoop stress,” notes Luke Anstice, geotechnical engineer at Reflex Marine, “so that the more load that’s applied to the anchor, the stronger the bond to the surrounding stratum, even in very weak, highly fractured ground.”
“While still in development, the novel aggregate locking system has the potential to make installation almost instant,” said Alun Jones, contracts manager at Reflex Marine. “If you have 50 turbines and 250 anchors to deploy, such savings on vessel costs and installation time can be significant.”
JAVELIN is designed to be installed at depths of as much as 100 m below the seabed, around twice as deep as traditional driven or suction piles. By accessing the stronger geology at greater depths, it’s possible to reduce the diameter of steel involved. Crucially, this means that boreholes are much faster to drill compared to large diameter solutions and the anchors can be installed using simple drilling techniques from a variety of suitable vessels.
“The slender nature of the JAVELIN anchor means you can handle it in the same way as a section of drill string,” says Laurie Thornton, director at MintMech, a specialist engineer experienced in offshore technologies. “With some simple, retrofittable upgrades, many vessels can both drill the borehole and install the anchor, eliminating the need for costly, dedicated deployment systems.”
Field testing
Reflex Marine first commissioned MintMech ahead of initial scale testing at a site in Cornwall. MintMech helped optimise the designs of the key components, such as the anchor’s tapered cones and other specialised parts, and fabricated a test rig.
“The initial proof of concept was iterative and quite labour intensive,” said Alun Jones. “We needed as much data as possible, so for the second phase we decided to move testing to a controlled environment inside our facility at Yatton. We needed a new test rig, so we approached MintMech again.”
“The Yatton rig was larger and more complex than the first,” said Thornton. “It featured a structural support frame equipped with a pneumatic cylinder, load cell and strain gauges, plus a rotating steel pipe that simulated the borehole.”
The successful trials helped Reflex Marine win more funding, with an award from the UK Department for Business, Energy & Industrial Strategy (BEIS) that enabled the third stage of the project, testing at an old China clay mining site in Cornwall. MintMech designed and fabricated all testing rigs used to load the anchors during land trials. Loads increased from 10 tonnes initially to over 350 tonnes.
“Working at Blackpool Pit let us analyse JAVELIN’s performance in geology similar to the Celtic Sea,” said Anstice. “The site also featured mudstone at a range of rock quality designations at different depths, it was the perfect test site.”
A 1:3 scale JAVELIN in a 10 cm borehole with 6 m of densified aggregate above it withstood 100 tonnes of load, while a 1:1.5 scale anchor with 12m of aggregate held fast at 361 tonnes. In both cases, the steel strand attached to the anchor failed before JAVELIN’s grip did.
The equipment to sustain a 1000 tonne land test has been commissioned, with MintMech providing the design, engineering and manufacturing inputs for the tensioning and load dissemination systems. The final step in the prototype development process will be to proceed to offshore trials.
“There are many innovative anchor technologies currently in development, but this is one of the most extensively field-tested solutions,” said Thornton. “At a talk MintMech and Reflex Marine recently gave, we seemed to be the only people with photographs of what we were doing. Designs, theories and 3D renders are one thing, but fabricating anchors, getting them into the ground and testing them is another.”
“Laurie and the team have very specific expertise over and above what we have internally,” concluded Jones. “From supporting with the original designs, facilitating the on-site testing and now devising potential installation methodologies, MintMech has enabled us to keep the project moving forward.”
Addressing practical and economic realities
Floating offshore wind represents a significant opportunity for UK renewable energy, but its success depends on overcoming critical engineering challenges. By combining Reflex Marine’s vision with MintMech’s engineering expertise, the two companies have advanced the development of a solution that addresses not only technical hurdles but also the practical and economic realities of scaling up floating offshore wind installations.
