rāl: a bar or series of bars, typically fixed on upright supports, serving as part of a fence or barrier or used to hang things on.
There are only so many ways to design swim fins. Our physiology dictates the efficient mode of swimming and good swim fins slap a couple inches of rubber to the end of your toes to increase the thrust. There are a few primary variables swim fin designers manipulate to arrive at their final design. The two main factors at work are flex and length, however throughout the almost a century of innovation, fins have developed unique rail attributes worthy of thoughtful deliberation.
At the genesis of modern fin design, Owen P. Churchill molded a pair of fins in imitation of a dolphin’s tail. Much like the dolphin tail, Churchill Swim Fins were smooth and lacked hard lines of geometry. His design provided the first step to increasing human swim propulsion.
Original Dolphin Photo: Leanne Smale
Churchill set the stage for the modern swim fin, but decades later Arthur Brown designed a fin which took advantage of stiff rails to provide a much more powerful fin. Brown realized strong rails could provide power both by stiffening the flex of the fin and by creating channels for water to flow through. Bodysurfers were also excited to feel the ability to use their fins’ rails to hold their line on the face of a wave.
Brown’s improvements were not unnoticed and Duck Feet were eventually adopted in lieu of Churchills by the Navy Underwater Demolition Teams. The “ribs” provided a structure to hold the fin in a stiffer position while swimming. If you imagine swimming kicks as “pushing off” the water around the foot, then a stiffer fin provides a firmer push off. The not so obvious improvement was made in channeling the water in a direction more beneficial to the swimmer’s movement. Imagine that same kick in a fin that pushes the water in all directions. The “push” a swimmer receives will give them general motion in the opposite direction of their kick. When Brown added the strong rails and the middle rib, it directed the water off the back of the fin and in turn created specific motion in the opposite direction of the kick.
For a long time bodysurfers had to choose between Churchills and Duck Feet, but in the last fourty years there have been many innovators with different takes on the fin rail. Fred Simpson‘s original Viper Surfing Fins had a heavy focus on rails. With the distinct double sided rails, Vipers looked a bit different than its predecessors. The second generation and more recognizable fins, lost the bottom rail. Viper’s rails are notable for their 90 degree edge and deep contour. No open-heeled fin before it had taken such an aggressive line. There are other notable rail adjustments. The DaFin design includes a wide and stiff rail that ends half-way down the blade. The Leblon Fin designer has separated the rail from the foot pocket to increase responsiveness of the rail to water flow.
Bodysurfing fin designers will continue to tinker with dimensions and rubbers seeking the ultimate balance of form and function. And we will continue to document and enjoy the benefits.
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Swell Lines 
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