System and procedure to transfer a load from a cargo barge to a substructure

System to transfer, at sea, a load on the fixed legs (3) emerging from water of a substructure, said load (2) specially fabricated in the construction yard and transported to said substructure by means of a suitable cargo barge (1), said load (2) and substructure (3) having a corresponding number of legs, said system comprising: (a) a prelaid mooring system in front of the substructure emerging from water comprising: (a') an horizontal sheave that can be opened useful to shift the mooring wire from a position to another; (b) a system to mate said load to the substructure comprising: (b') a main transfer system or extension system, called ALS (21), installed on the load legs (3); (b") a secondary transfer system or cargo barge release system, called BRS, installed on the cargo barge; (c) a system (26-29) to protect the barge sides and the substructure legs; (d) a cargo barge arrest system.