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The dynamic characteristic of interfacial debonded Ferry Ro-Ro’s stern ramp/door is studied by using finite element software ABAQUS. The effect of debonding on vibration responses of damaged stern ramp/doors is assessed by comparing numerical parameters of natural frequency shifts between intact and damaged models. Parametric studies over a wide range of debonding shapes to explore the influence of this parameter on the overall dynamic behavior of the models are investigated. Boundary conditions describing the loading conditions of the ship are evaluated. Four different debonding shapes with a similar debonding ratio, such as circular, square, through-the-length, and through-the-width, are investigated. To evaluate the effect of modeling techniques, both debonding shapes with and without spring contact element models are examined. Consequently, natural frequencies shift is being determined as functions of these parameters that enable to conclude the influence of debonding. The result has been shown that the debonding defect reduced the natural frequencies, especially in the square and circular debonding shapes. There is no significant frequency shift in the through-the-length, and through-the-width debonding modeling. Neglecting of contact leads to incorrect results, which significantly overestimate the value of natural frequency, so the spring contact modeling is recommended. The higher natural frequencies are found to be more sensitive to the presence of debonding problems. Using natural frequency shifts directly resulting from both intact and debonded models, the diagnostic can be performed.