Two-finned surfboards, often referred to as “twin fins”, have popped up time and again since the dawn of modern surfing, predating even the polyurethane blank. The first appearance of a two-finned surfboard came in the late '40s with the wide-tailed, parallel-railed, "dual fin" boards of Bob Simmons. His boards sported two "moon" shaped keel fins and are the precursors of the Mini Simmons and modern planing hulls. Simmons would continue to build and experiment with these boards until his death in '54 when the notion of a two-finned surfboard would fade from popular consciousness much like the man himself.
In '67 two fins would reappear again, first with the Mirandon brothers and their twin pin model, but then more significantly with Steve Lis and the advent of the twin-keeled fish. Again two fins somehow failed to develop drive, outside of San Diego, and by '73 they were rarely seen. Their hiatus this time was brief and by early '77 Australian Mark Richards had developed a fish-inspired board featuring two much more upright modern looking fins. He rode the design to four World Championships from '79-'82 and the twin-fin or twinny as Aussies call them became quite popular. Few managed to adapt to them the way MR did and with the introduction of Simon Anderson's thruster, a fin set up that would go on to dominate the next two decades of surf design, the twin fin was over.
Interest in two fins wouldn't return again until the late '90s and early '00s with rise of the retro and ride anything movements. This, along with several seminal films, the rise of the internet, and finally the closing of Clark foam in 2005, blew the door wide open on surfboard design. Suddenly there were no rules and people started giving anything a go. Two-finned surfboards are now a common sight at nearly every surf shop and beach. They have inspired offshoots such as the twin with trailer, essentially a hybridization of the thruster and a twin, and the split keel, a quad fin set up with a look and feel reminiscent of a fish's twin keel. Two fins can be found on anything from ultra-short stubby small wave boards to big wave guns, and come in a wide variety of shapes, aspect ratios, rakes and foils. Even boards utilizing Simmons' original moon keels can be spotted in lineups today.