Briggs Marine has successfully completed subsea cable installation work as principal contractor to Scottish and Southern Electricity Networks (SSEN) Distribution, supporting the electricity distributor with its commitment to delivering a safe, secure and reliable power supply to customers across the north of Scotland.
With the existing connecting cables nearing the end of their operational lifespan, the vital work improves reliability, resilience and safety of the electricity network for customers in the island communities of Arran, Orkney, Hoy and the Isle of Coll.
The works included the installation of four separate cable crossings, including an 11kv replacement cable between Langamull beach on Mull and Sorisdale on the Isle of Coll. A second 33kv cable was installed between Carradale and Arran with a further two 33kv cables crossing between Hoy and Orkney.
Working closely with the subsea cable team at SSEN Distribution, Briggs Marine mobilised and successfully completed the four separate cable installations and eight shore ends within 4 months.
The Scope of Works
Contracted to fully project-manage and install 15.6 km of new cable between Mull and Coll as well as 6.6 km from Carradale to Arran, the first phase of works required seabed preparation, including pre-lay boulder clearance, pre-lay grapnel runs (PLGR), potential unexploded ordnance (pUXO) investigations and route engineering.
From its own fleet of vessels, Briggs Marine mobilised ‘The Kingdom of Fife’ (KoF) with a PLGR spread to undertake route clearance operations. The ‘Forth Jouster’ was also mobilised as the Dive Support Vessel (DSV).
Trenching for the new cable was vital in order to provide protection and safeguard it from movement and other seabed users. Working with SSEN Distribution’s subsea team, areas that could achieve cable burial on land and offshore (where sediment and seabed topography allowed), were pre-identified for additional infrastructure protection to help safeguard local marine users.
In addition, Briggs Marine carried out cable jointing, testing and installation of landfall cable protection. Post lay video and multibeam echosounder surveys were carried out to confirm final locations.
Unique Challenges to Consider
The site presented a range of challenges including practical issues such as extremely ‘boggy’ ground conditions, making logistics difficult for the shore teams, strict environmental compliance requirements and a tight schedule.
Based on the West of Scotland, the project offered a particularly notable challenge in the form of protecting the local “Machair”, the name given to the unique habitat that grows upon the low-lying fertile grassy plain.
There are limited guidelines previously set for cables passing through the Machair areas. Briggs Marine worked closely with SSEN and the relevant governing body “NatureScot” to create a method that could be followed to ensure the Machair was conserved.
Craig English, Director of Subsea & Environmental Services within Briggs Marine commented,
“Wherever they work, SSEN Distribution is very proactive in engaging and consulting with communities, seeking views of local customers, and engaging with all stakeholders to minimise any disruption and ensure best practice is applied. It was important to everyone that the unique Machair with its inhabitants and habitats were protected throughout the operation.”
He continued, “Briggs Marine has demonstrated its expertise in considering environmental factors and its ability to work with public bodies, such as NatureScot, to help develop guidelines and procedures that will set a benchmark for any future works that could affect Machair.”
Continuing to work for SSEN Distribution, Briggs Marine has since undertaken further works to support the upgrade to part of the electricity network between Aultbea and Ullapool.