Solent Crossing - Export Cable Installation

A specialist joint venture between VolkerInfra and VBMS was awarded with a £13m contract by Southern Electric Power Distribution PLC to design, supply, install, connect and pre-commission test approximately 5.7km of 132kV submarine power cable across the Solent.

Facts and figures

Year of construction
2013 & 2014
Type of cable
NKT three core 132 kV XLPE Submarine Cable
Vessel
Fetsy L
Project categories

This project replaced one of the three subsea cables which supplies residents on the Isle of Wight. The project involved laying the cable from Thorness Bay on the Isle of Wight to Lepe in Hampshire by using a variety of installation techniques including Horizontal Directional Drilling (HDD) on the island, vessels and equipment to cross the Solent and open cut techniques at Lepe. 

VBMS completed the project in two phases: the first phase between September 2013 and November 2013 involved the installation of an 875 meter HDD at Thorness. The second phase started in April 2014 and lasted until July 2014.

In November 2013 the cable HDD duct was installed. The whole operation took place in less than 36 hours. Subcontractor Visser & Smit Hanab performed the drilling from the Isle of Wight and VBMS located the drill bit on the seabed.

 

The second phase commenced in April 2014, following the manufacture of a single length NKT power cable. Boundary conditions for the installation were challenging: water depths from 26m up to 2m and not only the beam currents of 4 knots resulted in tide stops but also the drying out of the lay spread.

 

The choice of lay spread was difficult as drafts were not allowed to exceed 1.5m. The cable was loaded onto a separate pontoon, which was moored alongside the Fetsy L to reduce the total draft.

 A new jetting was designed and built. A stinger supplied water to the burial tool and held the installed product whilst protecting these against the strong cross currents. Soil conditions varied from extremely soft layers to hard layers. Therefore, the burial tool was equipped with a powerful water supply and a soil displacement front combined with a towing capacity up to 40 tons.

 

In July 2014 on the Isle of Wight a shore pull of 1100m was performed through the HDD duct. Vaseline was used to reduce the pull tensions. On the Lepe approach we used a quadrant on skis to string out sufficient cable onto the beach. The Lepe pull in itself was completed after the lay spread left the beach.

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