Twin bilge keels?
If we look at a single keel with equal area to a pair of bilge keels as normally configured the single keel would be deeper and so, as per your desciption of a moment of inertia, its distance squared from the axis of rotation would be significantly greater and so would its dampening moment of inertia. But even comparing equal depth equal area single and bilge keels, the single keel would have a greater dampening moment of inertia because it is acting in undisturbed water.
Jeff
