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 smallest waves, and unable to hold a sustained turn, making it hard to ride in midsize waves and worthless in large surf. With the introduction in 1981 of the tri-fin board—a design that worked in all size waves—the twin-fin's day in the sun was over.
California board-design trailblazer Bob Simmons made a small number of twin-fins in the late '40s and early '50s, hoping to add stability to his wide-tailed balsa boards. Simmons himself favored what he called the "dual fin" design, and was riding one at San Diego's Windansea in 1954 when he drowned following a wipeout. In 1967, San Diego brothers Nick and Bear Mirandon, of Surfboards La Jolla, developed and marketed their split-tailed, two-finned Twin-Pin model. Mirandon's board sold poorly, but lead to the development of the Steve Lis–designed "fish"—another split-tailed twin-fin, adopted first by kneeboarders, then by stand-up surfers. At the 1972 World Surfing Championships in San Diego, Jim Blear and David Nuuhiwa finished first and second, respectively, while riding fish boards. Meanwhile, a thick, squat, square-backed version of the twin-fin, developed in part by California shaper Mike Eaton, and refined by Aussie Geoff McCoy, also came and went in the early '70s. By 1973, few stand-up surfers were riding twin-fins of any kind.
Australian world tour pro Mark Richards began working on a twin-fin redesign in 1976, after watching Hawaiian surfer Reno Abellira use a 5'3" fish during the Australian competition season. By early 1977, with input from Hawaii's master shaper Dick Brewer, Richards had developed his own 6'2" version—featuring a pair of six-inch-high fins set along the rails, about 11 inches from the tail—which he immediately described as "the ultimate small-wave board."
Richards adapted better than anyone to the maneuverable but hard-to-control twin-fin design, pushing it into a series of tight arcs across the wave face, and riding it throughout his 1979–82 world title reign. Dane Kealoha of Hawaii, and South Africa's Martin Potter were also outstanding on their twins. (Pro tour lore, meanwhile, holds that 1977 world champion and single-fin advocate Shaun Tomson lost his form for three years after switching over to twin-fins in 1979.) Tens of thousands of twin-fins were sold worldwide, and while the design produced a lot of off-balance arm waving and spinouts, it also introduced surfers to a new range of turning variables—all of which were better explored on the tri-fin Thruster, introduced in 1981 by Simon Anderson, Richards's world tour peer and fellow Australian.
Twin-fins have been manufactured in small numbers since the early '80s, mainly as kneeboards.