Maintenance of an offshore wind farm making use of an assembly of a floating harbour ship and a plurality of shuttle vessels

A method for use with maintenance of an offshore wind farm comprising a plurality of offshore wind turbines installed in open sea, in which the method comprises:

• providing a shuttle vessel for transfer of service engineers and/or goods to and from the wind turbines;
• sailing the shuttle vessel to one of the wind turbines;
• landing the shuttle vessel against the wind turbine for allowing transfer of the service engineers and/or goods between the shuttle vessel and the wind turbine;
• sailing the shuttle vessel to another wind turbine for allowing transfer of service engineers and/or goods between the shuttle vessel and that other wind turbine;
• and
• sailing the shuttle vessel to a harbour facility and mooring it there for allowing exchange of the service engineers and/or the goods between the shuttle vessel and the harbour facility before sailing the shuttle vessel out to another wind turbine;
• wherein the method makes use of an assembly of a plurality of the above-mentioned shuttle vessels and a seaworthy harbour ship which serves as the abovementioned harbour facility and for this comprises an internal harbour basin within outlines of the ship and a plurality of mooring positions for mooring the plurality of shuttle vessels to the ship when lying inside the basin, the basin being provided with an entrance opening for the shuttle vessels to sail into and out of the basin;
• wherein the method further comprises:
• sailing the assembly of the plurality of shuttle vessels and the harbour ship towards a halt position near or in the wind farm and substantially keeping the harbour ship in its halt position;
• and
• sailing the plurality of shuttle vessels back and forth between the mooring positions of the halted harbour ship and distinctive ones of the wind turbines for performing the maintenance thereto.