While "twin-fin" is used as a general description for any board with two fins, it mostly refers to a particular type of stubby small-wave board made popular in the late 1970s by four-time world champion Mark Richards. In waves under six feet, the Richards' model twin-fin had great advantages over its single-fin predecessor: a wider planing surface offered more speed, while reduced length helped open up maneuverability. On the downside, twins-fins were jittery and slide-prone in all but the sm...