Floating Wind

Most of the world’s offshore wind flows away from the coast, beyond the reach of bottom-fixed turbines. Floating foundations are expected to grow to a footprint of 10,000m2 and weights between 4,000t and 16,000t, requiring considerable infrastructure to transport.

As turbines reach higher, innovations such as the SK6,000 will allow the assembly to continue next to the quay, where it is most efficient. When maintenance events occur, our gantry solutions allow for fast repair at the turbine site, avoiding downtime while a suitable crane vessel is found.

Our offshore services team has transferred some of the world’s largest structures between land and sea; constantly innovating to find a way into the water that is most efficient, safe and cost-effective. 

Fabricating floating foundations will present significant real estate challenges for existing facilities. The scale of foundations also limits the number and type of fabrication facilities that can be used.

There are limited dry docks of suitable size to get these structures in the water, neither is a slipway launch appropriate for such huge objects. So, fabrication sites will need a large draft, or the yard space needed to support crane launching.

As the market opens up to these new entrants, the right modularized construction approach will be crucial to a project’s success. Designing modules so that they can be built, transported and shipped in the most efficient way shortens overall schedules and lowers whole-project costs.

Our work helps customers to manage all this through a single point of contact; diversifying the supply chain and allowing fabrication to take place where specialist workforces are most abundant. This allows more work to take place in parallel, by experienced teams, with the fewest interfaces.  

Due to their size, large real estate areas with good maritime access and sufficient ground capacity will be needed. Amongst the key criteria to meet will be the space to handle the increasing size of floating foundations, which are expected to grow to a footprint of 10,000m2 with weights of up to 16,000t.

It will be a challenge to find enough ports worldwide that can provide this, and infrastructure upgrades will be contingent on a reliable pipeline of projects being planned. However, with the right equipment, facilities located almost anywhere can enter the floating wind market.

Project-based upgrades that can deliver the required capabilities using operational rather than capital expenditure will be preferred. Mammoet can help to achieve this in an efficient and cost-effective manner, providing additional port space and lifting capability without interrupting existing activity.

We have helped major ports to develop their facilities with offshore wind in mind, providing additional space and ground reinforcement to marshal and store offshore wind components. Also, through innovations such as our SK6,000 crane, we provide temporary lift capacity, on-site only when it is needed.

One common approach has been the use of semi-submersible vessels, with components rolled onto the vessel using SPMTs. However, the time needed to prepare floaters for launch is significant, so this approach may not be cost-effective at scale, due to the time the vessel would lie idle.

A hybrid approach could be used, whereby the floater is lifted from both land and sea and lowered onto the water directly at the quay side. However, the use of several equipment types to perform lifts heightens the risk of a critical path failure, and so is not seen as a workable industrialized method.

One way to achieve this effectively and safely is through the use of a heavy lift crane. This approach allows smaller foundations to be placed directly into the water; cutting down several shifts of work to a single day. 

This approach has a number of other benefits: it mitigates the impact of swell on launching and requires a shallower draft than semi-submersible options, opening up more locations. It also reduces the requirement for specialized fastening and equipment when launching foundations. 

In fixed foundation offshore wind, jack-up vessels install turbines nearshore. But the water depth of floating wind projects – often between 80m and 100m – are too deep for jack-up vessels to operate in.

The complex engineering required to assemble floating turbines from a floating crane vessel rules this out as a viable long-term solution. Positioning jack-up vessels at port is also problematic, as they will soon be too short to build the tallest offshore turbines and would lie dormant for long periods between load-outs.

What’s more, modern 1,000t nacelles need to be installed 170m in the air; sometimes as far as 55m from the quay edge. This means that even when assembling from dry land, one of the world’s largest crawler or super heavy lift cranes will be required to complete the job.

Using Mammoet’s LR 13000, PTC or SK ranges of cranes allows ports and developers to shift spending on lift procedures into operational rather than capital expenditure. This can turn the smallest of ports into a functioning heavy lift terminal that exists for as long as the project does.

Hub heights reaching 170m will put turbines beyond the reach of many crane vessels, making repair at sea a costly operation with a significant risk of delay. The work involved in freeing a turbine and bringing it to port can make this method unviable, too.

Here, the challenges encountered during installation of the turbine are encountered in reverse; for example, the proposed port may have poor infrastructure, or be busy with other projects. So, alternative ways of conducting maintenance on the turbine in situ are needed.

Luckily, the floating wind sector can benefit from established solutions that have been tried-and-tested in other industries. Mammoet offers specialized expertise in performing repairs to offshore assets in situ and has developed modular solutions that offer important advantages for floating wind.

Our 200t module lifting system uses the turbine itself as a means of support and can be deployed from even small fishing ports. This makes it possible to execute turbine maintenance, quickly, cost-effectively, and without the need for a crane vessel at all.