Tow Out Calculations For Floating Wind Turbines

Abstract

Floating wind turbines are becoming an important part of renewable offshore power generation, offering an opportunity to deliver green energy. The floating nature of the substructures permits wind turbine placement in deep water locations, probably out of sight of land. This paper presents the tow out design method requirements for the installation of floating offshore wind turbines. Most existing floating offshore wind turbines substructures are barge, semi submersible, TLP and Spar types and their installation methods have been developed from those used on offshore oil and gas structures. Whilst the turbines are derived from those used on fixed bottom offshore wind turbines. The paper summarises the weather window limitations for the various substructure types and installations phases, including the transportation to and from the offshore site and during the connection of mooring lines and electrical cables. The choice of construction materials i.e. steel or concrete, influence the draft of the substructure at the fit-out quay and hence during the tow offshore. Semi submersible and barge types are of shallow draft and can be fitted out alongside a quay. Spar types typically require deep water for construction in sheltered inshore waters. The Tension Leg Platform (TLP) floating wind turbine has minimum water plane area and hence has low intact stability during ocean tow and thus TLPs may require modified crane vessels for offshore installation. The paper will present recent advances in the tow out requirements of floating offshore wind turbines. Data will be provided on intact stability, damage stability, tow forces and motions during tow from fit out port to the offshore location.