A structure for transport and offshore installation of at least one wind turbine or underwater generator includes a U-shaped floating hull having lateral arms. Each lateral arm has at least one leg vertically movable by the hull in flotation, and at least one assembly for supporting a wind turbine or underwater generator. The assembly includes two shuttles opposite each other and each combined with a leg and each having higher and lower pairs of arms which are pivotably movable between a retracted position and an active position tilted against a mast of the wind turbine or underwater generator.