Understanding Mini Design
In John Elwell’s detailed study of the contributions Bob Simmons made to surfing, published in a 1994 edition of The Surfer’s Journal, he wrote an analysis of the Simmons board, here are the highlights:
“The Simmons surfboard is as strange an apparition today as it was when it first appeared. In its time it broke all the rules of the day. It represents a shift from heavy displacement to light displacement along with the application of scientific theory. It was a radical departure, far ahead of its time, like the designer, and misunderstandings hindered its full acceptance. Bob Simmons disregarded criticism and just went surfing, which was his great love; his surfing proved the validity of his boards along with their use by a small cadre of followers.
“From what he said and the body of research he had in his possession, along with a visual appraisal, one can get an idea of what he was pursuing. He was an erodynamicist and a mathematician. That viewpoint must be kept in mind.
“The boards had maximum width. Width was favored for the least resistance. Width plays a key role in delivering kinetic energy to the airfoil rail, the leading edge, that gives deflection. All planing hulls are deflectors. The airfoil is a special shape that is calculated. Width divided into length, is aspect ratio, giving a magic number related to lift. Width also allows the hull to leave a clean wake. An impressive example of the value of width is the bodyboard.
“The wide, unusually cambered, uplifted noses created a lot of criticism. The unknowing critics said they were pushing water, but they were in fact working, spreading the water, momentarily, to the high pressure rails before take off. In a tough spot, where the nose comes in contact with the water, in a steep takeoff or large chop, they lifted. Changing the noses was not a big deal to him, saying they stick out when we surf. He rejected points as too fragile and dangerous. Some of his early boards had points. Constant form, flat noses are perfectly acceptable in smooth water. Simmons opted for camber, because sea conditions can change rapidly due to weather changes.
“The outlines were fair parallelism, contiguous rails, fared-in near the tail for clean stable running. Non-uniform outline shapes were rejected, because of eddy flow resistance that increases with planing speed. This occurs at 10” in width. He is on record that trying to modify paddleboard shapes into surfboards was wrong; destroying the wide tail reduced early lift and clean resistance wakes. Those forms pulled the rail away from the wave and required a single fin, partly corrected with a tri-fin today, which undoubtedly would have been rejected, because of increased appendage drag. Rocker was rejected for reasons made obvious by his theory. ‘Ya just don’t need it!’
“He rejected the notion that wide tails were the cause of ‘spin out,’ and considered it a fin problem. He moved a small fin to each outboard rail at the end and towed them in to 10º. This is because the water is moving the fastest at these points as it leaves the hull. A single centered fin is in the low pressure area of the board and away from the wave. He simply expressed, you need more fin at low speeds and less at high speeds. Simmons and his ‘test pilots’ never spun out with dual fins, surfing the biggest and hardest breaking surf. However, he warned that non-uniform hull shapes could ‘spin out.’ This is because uneven side pressures build up, inducing a possible sudden yaw. These shapes require a deeper fin, increasing appendage resistance as the board surfs forward and sideways. He noted with criticism that narrow tails, give a tubing, sucking wake. Anything that has eddy flow resistance, was a ‘disaster’ and ‘not the way to go!’
“The rail and fins had a ‘chord value’ percentage dimension, to allow a smooth release of water flow, allowing the least amount of cavitation. An illustration was contained in a text he had. He dismissed this with a cackle by saying, ‘Generally just lead round, end thin, and that is good enough.’ A true planing hull adjusts itself with speed, where it eventually works itself to a minimum in the aft inside section of a surfboard, unless as Simmons and others found out, it leaves the water in a launch and a skip. He dumped ultralight to keep the boards in the water. Due to the extreme thinness in the nose and tail, he recommended two coats of glass, and even a coat of marine fiberglass paint to protect the board from the destructive rays of the sun, ‘… if you want to keep it.’ He added, ‘the extra weight doesn’t make that much difference.’
“The center of gravity, was precisely placed on these boards. Load has to be forward of lift, a commonly known fact in aerodynamics and naval architecture. Most of his boards would balance on a sawhorse in the middle or slightly forward. The decks were domed smoothly into the rails, shedding water rapidly off the airfoil, this concept greatly reduced unneeded weight. A density calculation was done of materials to get an exact flotation for the weight of load, to barely support the rider. Some surfers, skeptical of this, asked for more flotation and he complied reluctantly.
“A very few of his boards had concave bottoms. Simmons said he did this to get air into them briefly, reducing the suction. The center of the hull has a low pressure flow down the center area anyway. He reduced it even more with a concave. But his concentration was focused on what was happening out on the rail.
“Simmons had piles of computations in advanced math. (All of these are apparently lost, along with test models.) His boards were a complex creation. His efforts were the result of a comprehensive scientific approach using experimentation and Newtonian mechanics. However, planing hulls suffer a penalty at low speed, struggling to get over the hump. Resistance points can be identified where water breaks away in small waves. Simmons attempted to solve this by flow slotting aft of the nose, and spoiler slots in the tail. Only a few boards had this feature. It was very difficult to do correctly. Each of these boards had to be surfed without glassing, with a tack coat of resin. This was applied ‘boomerang science;’ throw and adjust to desired performance. He was also checking the desired attack angle; the immersed, thin-wide tail had to be between 15-20º. This was the secret for quick and early lift for gaining position. Strategically, Simmons wanted to be in the wave first and as soon as possible, for the right-of-way, second he wanted speed, to cover distance for long rides. Big waves and long rides were his criteria for performance. Everything else was folly! He was successful at this. It was commonly said in his day, ‘No one has ever gone as fast on a surfboard!’ It was noted by contemporaries the he usually got the best rides.
“Length plays a role in speed, to a point. Appropriate length captures the maximum principle of resurgence, as water is pushed away, it rebounds and assists the hull. The only way a non-contiguous narrow shaped form can come close to a wide hull is to increase length, but it will never lose its lateral instability. He settled for a 10’6″ for bigger surf and 8′ for quick, hard breaking inside breaks.”