The vessels are enhanced GustoMSC 9000C designs, meaning self elevating vessels with four jackup legs and a large installation crane. The design incorporates important features from inhouse experience from offshore wind installation and maintenance work, as well as 160 years of maritime history. The governing thought throughout the vessel design phase has been to make the vessels as operable and flexible as possible, to perform the required tasks for loading, transporting and erecting wind turbine equipment offshore. Open deck space and accessibility achieved e.g. by the crane wrapping around one of the legs, plus the operability of a high performance jacking systems designed for fast and frequent jacking operations as required by the wind industry, are vital key words in this respect.