Momentum on the Following Sea
Riding on the crest of a wave, a quintessential surfer glides on water propelled by nature's energy. He smoothly slips into a steep surging swell as it transforms into a cavernous vortex. Effortlessly he turns across its emerald glistening surface. His ride is seamless as he maneuvers around and through powerful steep lurching sections without loss of momentum.
Evolution and Modern Surfing
Evolution changed surfing forever, gone are seamless flowing rides. A quintessential or traditional surfer differs from a modern surfer. A modern surfer flies through the air, sometimes high above the wave. He flies down the wave and lands tail first, following with a spinning turn after recovery. Flight adds hard flat landings which may require recovery or regenerating momentum at the cost of fluidity. Loss of momentum usually ends his ride. If a surfboard can keep moving after a hard impact with the wave, the surfer may recover. This is achievable with an alternative bow shape. A shape that moves water out of his path instead of forward in his path. Both the modern surfer and traditional surfer can benefit from this alternative.
Evolution has also brought surfboards to its performance limits. Surfboards can be compared to boats crossing through rough seas. Both vessels ebb and flow through an unpredictable ocean, rising and falling at the whim of the sea. Boats climb and churn up large swells. Once over the top, they launch skyward into the air, landing hard on their bows, creating large wakes. The landing robs forward momentum and pitches cargo and passenger. A boat can add power to regain momentum and face the next swell. A surfer cannot add power and is left with no momentum, in a hard collision with water. It is the sudden loss of momentum, in hard flat landings that impedes surfboard performance. Reducing the loss of momentum will allow a modern surfer to progress further and perhaps complete his ride. This may be achieved by using round or V-bows similar to boats.
A planning boat optimally rides on its aft half like a surfboard. Planning hulls differ from hulls of ships and sailboats. They can gain enough speed to rise to the surface hydrodynamically and eliminate the forward push of water. At lower speeds, the front half enters the water. When the forward half is in the water, it clears a path, pushing water aside. Speed is restricted while the bow is in the water, but; the Vee bow shape sustains momentum. Note in the video how the bow parts water and cushions impact. The Vee bow cuts through water and conserves energy, sustaining momentum.
Flat bottom surfaces are designed to create lift, sometimes hydrodynamic lift is not desirable, especially in rough seas. Most surfboards are flat from nose to tail. Flat bottoms do not penetrate the surface deeply. They resist penetration and rise to the top with speed. Water cannot move out from under a speeding flat bottom boat instantly. Water resists movement and supports the boat on the surface. The lift is not with buoyancy, but; with upward pressure created by speed. The water's surface becomes somewhat impermeable and stationary, with speed. Water pushes against a speeding flat hull generating lift. Lift becomes forward resistance pushing against the flat bow of the boat. To reduce forward resistance boat bows are pointed and Vee or round shaped. Note in the hull pictured above, Vee becomes less pronounced toward the rear. Less lift is generated near the bow and more at the stern. A more subtle design works with surfboards. The above hull planes at high speed and displaces water with hard impact and low speed. A displacement bow moves faster through water (in water) than a flat bow. The flat bow is faster when it rides on the surface, but; not below the waterline. Flat bottoms can stop with a hard impact with the water. A semi-displacement hull may provide a solution for surfboards. Semi-displacement boards can ride on the water at high speed and through the water at low speed. They can push water aside with hard impact and maintain momentum.
Flat bottom boat bows will ride in the water at low speed. The hull can move water at low speed. Unlike a Vee bow it does not part water immediately, it first pushes water forward in its path. The process consumes energy and robs momentum. This is called wave-making resistance. The boat creates a bow wave as it pushes water. Flat bows are designed for flat smooth water. These hulls are pushed backward in heavy seas. This rule applies to surfboards. Push back in surfing, occurs in a nose pokes or a pearl dive. In a pearl dive, resistance is produced by water pushing against a speeding flat surfboard underside nose bend. Pressure on top is generated by the surfer's weight. Water pressure on the bottom produces most of the resistance that allows a surfboard to plane on the surface. The same pressure applied to the bent underside produces a reverse force which launches a rider.
The most common form of flight in surfing is the free fall drop. All surfers have taken off late to find themselves in the air. With hair raised standing on end, they enter a high speed dive into deep and dark depths. In a very steep dive the nose submerges underwater. On shallow dives, the nose rocker keeps the tip up, but; water pressure on the flat underside pushes the board backward. Again, flat surfaces generate pressure on water with speed, Bernoulli's Principle.
Skills have evolved with flight and surfers are landing free fall drops. Often the ride is not completed, especially when the landing is on the underside of the nose rocker bend. This section is comparable to a bow in boats. Boat bows are deeply veed as depicted in the above photo or round like a sailboat. Surfboard bows are flat. An average surfer can recover from a shallow dive with the right hull shape. The bow should not be flat. A semi displacement hull is most the versatile. It will plane on its aft half like a planning hull and part water with a round or Vee bow. The semi displacement hull sustains momentum.
The modern surfer is very skilled. He lands aerials on the wave often losing little
momentum. High aerials are difficult to complete. Skill is dictates equipment choice. Personal preference is a factor. Designs differ and can improve performance, but; choice is the decision of the rider. Equipment modifications though scientifically sound, may not suit the preference of the rider. All designs have limitations.
In the past, surfboard bows were round. In the sequence below legendary surfer Eddie Aikau successfully rides out of a shallow dive. Modern surfers rarely accomplish this on flat bottom boards.