Stiffened panels are essential structural elements in marine structures that often need openings for various operational uses, like access and pipe routing. The ultimate strength of the structure under compression can be significantly diminished by these openings, which result from stress concentration and a smaller cross-sectional area. This investigation employs nonlinear numerical analysis to examine the influence of three primary geometric parameters on the rate of ultimate strength reduction in stiffened panels featuring circular perforations. The simulations used ANSYS software, applying the Shell 181 element type, and included large deformations, elastic-perfectly plastic material behavior, and initial imperfections. Symmetric boundary conditions based on the (1/2+1+1/2) span model were employed to eradicate errors inherent in conventional boundary conditions, and the model was corroborated by earlier studies. Results from the parametric study show that the ultimate strength decreases nearly linearly as the ratio of opening radius to plate width (R/B) rises from 0.20 to 0.35. The absolute ultimate strength of the structure is notably increased by enlarging the stiffener size, yet the percentage reduction rate associated with the opening size remains unaffected. Increasing the plate aspect ratio from 3 to 5 slightly amplifies the sensitivity of the structure to existing the opening. The most important result of this investigation addresses the longitudinal location of the opening. Relocating the aperture from the central inter-frame region towards the extremities intensifies interfering buckling nodal points, elevating the strength reduction from 5.4% to upwards of 8%.