45,000 tonnes of armour stone, one new harbour defence

As part of the construction of a new offshore breakwater at Cowes Harbour, we were appointed by Boskalis Westminster to support the delivery of the permanent rock armour protection. Working from the completed sand and shingle core, our role focused on placing armour stone with precision to form the breakwater’s outer protective layer. 

Project overview

Delivered over 10 weeks, this £2.2 million package formed part of the wider Cowes Outer Harbour Breakwater scheme on the Isle of Wight. 

The 350-metre-long detached breakwater was designed to provide greater shelter within the harbour, helping protect local infrastructure, harbour users and future development along the waterfront. In partnership with Boskalis Westminster, we carried out the final trimming of the breakwater core and the placement of more than 45,000 tonnes of rock armour to complete the structure. 

The full works

Using GPS-equipped long-reach excavators, the team undertook final trimming works to ensure the core was accurately profiled ahead of armour placement. A total of 44,500 tonnes of material was then placed to form the breakwater’s protective outer layer, including: 

• 15,000 tonnes of filter stone 

• 3,500 tonnes of intermediate armour stone 

• 26,000 tonnes of primary armour rock 

The accurate placement of each rock layer was critical to achieving the required design profile and ensuring the long-term performance of the structure in a demanding marine environment. 

Precision placement in a marine environment

Constructing an offshore breakwater requires a high level of accuracy, particularly when working with large armour stone in exposed coastal conditions. 

GPS technology enabled operators to precisely trim the core and place rock to the required tolerances, helping ensure the completed structure matched the design specification. The combination of specialist plant, experienced operators and careful sequencing allowed the rock armour layer to be installed safely and efficiently. 

Working within an active harbour environment also required close coordination with the wider project team to maintain programme progress while operating safely around ongoing marine activity. 

Supporting long-term coastal resilience

Breakwaters play a vital role in protecting harbours from wave energy, reducing erosion and creating safer conditions for marine users. The completed armour protection at Cowes Harbour forms the outer defence of the new breakwater, helping safeguard harbour operations and supporting the long-term resilience of this important coastal asset. 

Projects such as Cowes demonstrate our capability in delivering specialist coastal and marine works, combining specialist plant and experienced teams to operate effectively in complex marine environments.