Since 1998 feed-forward networks have been applied for the separation of hadronic W-decays from background processes measured by the DELPHI collaboration at different center of mass-energies of the Large Electron Positron collider (LEP) at CERN. Prior to the publication of the 189 GeV results intensive studies of systematic effects and uncertainties were performed. The methods and results will be discussed as well as the results from the different energies and compared to standard selection procedures. Now feed-forward networks are also tested to improve the separation strenght in the semileptonic channel of the W-pair production. First results will be presented.