New solution allows huge XXL monopiles to be stored and transported using existing support structures

Three 430t jacking systems, each with two towers, supporting a cradle system of 1,000t capacity.

As offshore wind turbines grow, their foundations are increasing in size, making transport and storage more difficult. Mammoet’s new jacking and cradle system minimizes upgrades to grillage and sand bunds, helping customers to reduce costs.

Monopiles are colossal cylindrical steel foundations that connect wind turbines to the seabed. They can weigh in excess of 3,000 tonnes and be over 120m long, and their growth shows no signs of stopping.

As developers build taller turbines, their foundations are getting larger in diameter and also longer - moving beyond the capabilities of existing handling equipment. This makes their transportation to site and storage on site more challenging.

Also, when an XXL monopile is lifted, its self-weight causes big deformations. This means that monopiles need to be raised higher than their supports to be loaded or unloaded.

Mammoet’s new jacking and cradle system adds 60cm of additional stroke over and above the standard SPMT systems. This allows customers to continue using existing support structures as monopiles grow.

This technology will also allow other links in the supply chain to reduce project costs.

As offshore wind projects become more globalized, monopiles are travelling further distances. So, Heavy Transport Vessels need to have larger sea fastening to support monopiles during voyages.

Because of this, there is less and less clearance when loading and unloading large monopiles using SPMTs. Mammoet’s new jacking and cradle system can lift monopiles higher, allowing more sea transports to take place using existing support structures.

The system comprises two elements: jacking spacers that sit between SPMT modules to generate greater stroke, and hydraulic, foldable saddles that cradle the monopile so it can be supported at higher points, to prevent excessive ovalization.

Each jacking spacer has a capacity of 430t split across two towers - with multiple units in use per transport configuration. The system slots between SPMT modules, so transport configurations maintain the same minimum ride height. This enables grillages and sand bunds to remain as low as possible, again saving on costs.

Each monopile saddle has a capacity of 1,000t and can handle monopiles up to 12m diameter. By using the system, Mammoet customers can maintain the existing methods of supporting and moving monopiles, even as they grow from 8m to 10m diameter, and beyond. This reduces whole-project costs right through the fabrication, shipping and storage supply chains.