The estimation of the ship hull girder ultimate strength under vertical bending moments as close to real behavior is vital both for design stage or seagoing life. The maximum load carrying capacity of ship hulls called ultimate strength depends on a number of factors including the strength of the structural material, initial distortions, dimensions and layout of the structural components, the component discretization (idealization) of hull girder section. In this study, the main target is to evaluate the effects of hull girder section component discretization, initial deflection of plates and residual welding stress and 50% corrosion margin for individual structural components on the ultimate hull girder strength. Within this context, hull girder ultimate strength calculations are carried out for ten benchmark ships' cross sections for validation of HULT developed by authors, firstly. Next, to reflect the effect of diverse key factors, selected ships among ten are analysed for different scenarios using progressive collapse analysis based method HULT and with IACS-CSR formulations. Critical collapse moment values of ten mid-ship cross sections are calculated and shown to agree well with the results of previous studies. As a result, both the accuracy of HULT, as well as the effects of diverse key factors on ultimate strength are shown clearly by case studies.