Seaworthiness: rolling motion in waves

The rolling due to waves could lead to critical failure. It is particularly dangerous when the natural period of the rolling motion coincides with the encounter period of the waves. If the frequency of the waves is far from the natural frequency of the craft, the rolling amplitude will not grow indefinitely with time. On the contrary, if the frequency of the waves is close to the natural frequency, the amplitude of the rolling motion will increase. Therefore, a vessel whose natural period stays far from the typical period of waves is convenient. But how should we attain this objective? By increasing the yacht’s natural period or rather by decreasing it?