Keep in mind that the longer the vessel, the longer the wave it generates as it moves faster. A 40-foot sport fisherman creates only short waves that will bounce you quickly, a 500-foot tanker makes much longer ones that are more like ocean swells. And of course, any waves will build in amplitude as they encounter shallow water. Consider the mouth of the Potomac when those long ocean swells roll into it from the south. Or the coast of Japan when a tidal wave approaches. — Tom Dove At Home in the Center of Entropy.