Cable trenching in the Southern North Sea for Fendercare Marine - HelWin/SylWin HVDC.
James Fisher Subsea Excavation was contracted to trench cables to a depth of 1.5m below seabed in the German sector of the Southern North Sea.
Location 1: The cable bundle was laid across three mattresses where it crossed another cable. To provide lateral stability, JFSE was required to trench the cable for 50m either side of the crossing location.
Location 2: Trenching of the cable bundle had been completed up to 140m of the HelWin Beta platform. 120m from the platform, the cable bundle split into three separate components, 2 x power cable + 1 x FO cable, these cables were to be individually trenched up to the bend restrictors at the platform J-tube inlets.
Location 3: A 30m length of cable was to be trenched at the SylWin Alpha platform.
The SP6000 equipment spread was trucked from JFSE's base in Oldmeldrum, Scotland to Great Yarmouth in South East England where it was loaded onto the SSV Vos Shine. Deployment of the SP6000 was undertaken using the vessel's knuckle boom crane, operations being undertaken in seas up to 1.5m.
Location 1: The cable bundle was successfully trenched to 1.5m depth in less than 2 hours.
Location 2: The cable bundle and its individual components were trenched to the required depth in 5 hours. The total length completed was 380m.
Location 3: The 30m length was successfully trenched in 30 minutes.
The project was completed in challenging conditions, with some strong currents being experienced. The bights in the cable also presented a challenge, but the non-contact method of excavation employed by James Fisher Subsea Excavation and their SP6000 equipment is ideal for this type of application.