Nose Poke Part III/Gravity Force
Surfing is a gravity sport similar to skate boarding, skiing and snowboarding. Surfing differs in that the mountain changes and moves. Wave motion adds movement and danger to surfing. A fast moving breaking wave affects a surfer by either giving him a boost or a terrible beating. Ideally a surfer prefers to ride within the breaking wave using gravity to propel him. Kinetic energy is generated by gravity forces on the surfer's weight. Gravity is a surfer’s primary source of energy.
Surfers must balance the forces of gravity. For this discussion gravity is simplified, not without recognizing a surfer's dedicated discipline of balancing and controlling gravity forces. The center of gravity (CG) is a theoretical point on a surfboard where it is balanced on both horizontal and vertical planes. The further forward of center a surfer moves on a board, the more it dives and gains speed. The further aft of center a surfer rides, the more it noses up and stalls. Weight left of CG produces a left turn and weight to the right generates a right turn. Bottom turns and cut backs by skilled surfers are accomplished with a combination of aft and complex horizontal weight shifts. A surfer's timing and rhythm keep him in sync with the wave. Modern surfing with aerials, include turns in the air. Surfer accomplish all by balancing the forces of gravity.
A nose poke occurs when the tip of the surfboard pierces the surface of the wave. The surfboard is nose down relative to the center of gravity or diving. Gravity forces drive the surfer’s weight downward nose first. Speed and weight are factors in a poke, if a surfer can decelerate or unweight, he has a better chance of staying on the board. Often control is lost and gravity takes over. When the board stops in a nose poke, it is due to resistance or friction. A long held belief, is that water slows the submerged board and causes it to stop. This is only part of the explanation. To keep the nose above water, nose rocker was increased. Water does create resistance, contrary to the old belief; wave making resistance causes a stop. This is a review of a few principles from previous articles. Resistance is created by the surfboard's bow, which is the bottom bend produced by nose rocker. Increasing rocker increases wave making resistance or friction. The more nose rocker a board has, the more resistance it creates. Nose rocker slows and stops the board in a nose poke due to a sudden impact on a flat bow. A board moving at high speed, is capable of moving a few meters underwater. The nose poke often stops immediately, an indication is a launched rider. The board does not travel very far underwater because most bows are flat.
Water's cohesive properties resists impact by fast moving flat surfaces, due to hydrogen’s inter molecular bond. This is hydro dynamic lift at work. Water resistance is supporting and blocking the nose. A flat bow accumulates water in the board's path. Boat and canoe hulls move water directly out of the vessel’s path with a round or vee hull. These hulls may recover from a shallow poke, by not stopping and by not pitching the rider. A flat bow is designed to ride on the surface. It displaces water inefficiently and too slowly when a speeding board hits water. The board depletes its kinetic energy and stops, while the rider with his kinetic energy continues through the air. Very skilled surfers over come wave making resistance by dragging their bodies. Surfers absorb impact with their bodies to keep the board moving in a free fall drop. Weight is taken off the board as the surfer’s body slams into the face of the wave. The weight removed from the speeding board, prevents the bow from hitting hard and stopping. The board does not abruptly stop and the surfer is not launched.
Surfers sometimes combine a body drag with a side slip by breaking their fins free. This gives an advantage to a backside surfer negotiating a steep drop. This advantage only goes to a very skilled surfer.
Referring to the inclined plane diagram, by removing his weight from the surfboard, the surfer reduces mass mg in three vectors. This reduces acceleration, but; the bow wave resistance or friction (f) is simultaneously reduced, allowing forward progress.
The body drag is not an easy feat as the following trailer demonstrates. Flat bows produce a hard flat landing which launches many surfers.
Getting off a surfboard in flight is a special skill many normal surfers lack. An alternative is to cushion bow impact with a vee or round shape like a boat or canoe. This is ancient knowledge originating centuries ago with the birth of ocean exploration. The design may not save all nose pokes, but; a surfer can recover from a shallow one.
In closing, we design high performance surfboards using computer driven machines. Technology is only a tool, ancient knowledge is wisdom. Explorers from the past used ancient technology and navigation to cross oceans. Ancient knowledge can improve the future.
Galileo's inclined plane from the Renaissance Era.
Watch how an outrigger canoe displaces water with its bow. A surfboard can do the same.
Pictures youtube and google images, Videos from youtube.