As known, the variation of the metacentric height of a ship in irregular waves is not a pure linear process, particular when a ship has large beam to draught ratio and large flare near the waterline at bow and stern. This kind of unconventional hull form is usually adopted for modern RoRo-ship, cruise-ship etc. which allows large cargo space and high service speed. In this paper, the GM-variation is derived into a function series with respect to the variation order and represented by the Volterra system. The transfer functions for the different orders are integrated numerically or analytically through expressing the sectional beam, area and moment in Taylor’s series as function of the momentary water line. Thereby the explicit relationship between the hull form and GM-variation can be obtained. The numerical result has shown the significant effect of the second order term in the Volterra system on the GM-variation in waves. Hence, the non-linear characteristics of the GM-variation in an irregular wave can be easily analyzed by means of available nonlinear probability theories or Monte-Carlo simulation technique.

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