Gary Howland, Renewables Sales Manager for Trelleborg Offshore, says: “Trelleborg Distributed Buoyancy Modules (DBMs) developed for deepwater support of umbilicals and risers in the oil and gas industry are ideal for this application; helping reduce project risk by using proven technology.”
Trelleborg’s technology is already in use at the Hywind floating offshore wind turbine installed off the west coast of Norway.
Trelleborg Offshore designed and supplied 45 off polymer-coated syntactic foam DBMs which supply buoyancy support for a 3 tonne, 100 meter section of offshore wind turbine cable as it exits the wind turbine spar and descends to the sea bed at -220 meters.
The buoyancy modules include an internal clamp for secure fastening and precise positioning on the cable. The cable is supported mid-water in what is known as a ‘Lazy Wave’ configuration, featuring gentle long radius curves that minimise stress on the cable while accommodating natural movement created by wind and waves.
Howland continues: “For optimum buoyancy under different sea conditions, the precise position of the buoyancy modules on the cable is pre-calculated. The positions must be maintained, despite stresses during launch and in operation. The clamp is crucial; the design, material selection and manufacturing technique are critical in ensuring the finished clamp maintains the buoyancy module position, during cable contraction and expansion, over the 20 year lifetime of the project.”