Navigation aid towers composed of a column and a submerged gravity base have been constructed on sloping
sea beds to shore.However,as large horizontal and vertical wave forces act on the base,there is a high probability
such structures will slide or overturn.In order to sustain stability,it is generally necessary to increase the weight or
extend the width of the base of the structure and reduce uplift wave pressures that form the vertical forces.In this
study we proposed increasing stability using a simple reduction method for perforating the base so as to decrease
uplift forces. A 1/16.3 scale model test was conducted on box shaped bases with five different sizes of penetrating
holes to examine the reduction effect on vertical wave forces.We also conducted a numerical analysis using potential
theory.This paper also describes the alpropriate inertia force coefficients of the experimental and theoretical wave
forces using a conventional formula, the Morison’s equation, to evaluate the vertical wave forces.