DNV GL has launched Twisties, a new joint industry project (JIP) aimed at standardising and improving offshore wind logistics.
The increasing size and quantities of wind turbines installed offshore means that a change in requirements is needed for shipping project cargo between manufacturing and marshalling port facilities, and feeding wind turbine installation vessels offshore.
Conventional feeder vessel operations have introduced many challenges, including operational limits on wave heights and wind speeds. DNV GL has identified that a fast feeder vessel using a RoRo (roll on, roll off) method of logistics transfer can avoid both wave-limits and the tight wind speed limits often associated with lifting blades offshore. It is this constant requirement for handling project cargo of a repeatable form, with bolted flange connections, which has brought about an industry desire to optimise and standardise transport logistics and sea-fastening arrangements.
The wind industry has made attempts at unitisation, such as grouping three blade sets into a ’unit’. Modular twist-lock, stackable blade racks are now commonplace on the decks of installation vessels. DNV GL has taken this concept and proposed a method for unitisation, by using modular transportation and sea fastening frames, based upon standard 20-foot cargo container twist-lock centres.
Twisties ensures that cargo can be transported on existing vessels arranged for containers and is said to avoid the need to develop new specialist transportation and installation vessels for next generation 10MW+ offshore turbines.
Transporting turbines and other wind farm components using Twisties is shown to significantly lower construction programme durations to ‘single season’ phases, according to DNV GL. It is also said to allow for greater quantities of turbines to be installed using a defined number of wind turbine installation vessels. The concept demonstrates cost savings in some cases of above 25% compared to conventional installation practice, DNV GL said.
Chris Garrett, Senior Offshore Wind Farms Engineer, DNV GL said: “Establishing a JIP will de-risk the implementation of this technology and promote the unitisation of wind project cargo. This continues our commitment to reduce the cost of offshore wind, as outlined in DNV GL’s Offshore Wind Cost Reduction Manifesto. Understanding the technicalities of current wind industry transportation methods enables us to demonstrate the vast benefits that a standardised unit approach will bring to the entire industry.”