Problem: Surfing evolved with the introduction of flight. Surfers are landing high aerials and airborne free falls. Surfboards may abruptly stop at high speed on impact with water.
At high speed, hydrodynamic resistance pushes against the flat underside at the nose rocker bend, stopping movement.
Research Subjects (follow): Physics, Wave Making Resistance, Cohesion and Adhesion, Nose Rocker, Gravity Force, Bow, Marine Technology, Movement Phases, Kinetic Energy, Hulls.
Soluion?: Semi-Displacement Hulls with moderate nose rocker can push water aside minimizing deceleration, allowing transition to planning with hydrodynamic lift.
Physics is the study of matter moving through space and time. Movement through space generates waves. Every action or motion generates waves. We constantly generate waves in our daily activities. Examples are air waves, produced when we move and sound waves generated by speaking or yelling. When a surfer rides a wave, he simultaneously creates waves as he move through water.
Physics defines a wave as an oscillation moving through a medium, which transfers energy. The surfer’s medium is water, he transfers energy to water by displacing it.
Wave Making Resistance
Everything moving through water generates waves. A splash is a wave and a wave is also called a wake. Wake production can slow and stop a surfer. A bow wave which forms under a slow moving surfboard, is water the surfer moves with his energy. Energy transferred to water must be replenished continuously, or the ride will end. The main source of energy for a surfer is gravity, which supplies kinetic energy. When a surfer does not have enough kinetic energy to displace water out of his path, the ride ends. An example of this is a pearl. In a pearl dive, the nose of the surfboard submerges under water, and the surfboard stops. A surfboards stops in a pearl for several reasons. One reason is the surfer burns up his kinetic energy and has no means to acquire more. Another reason is it creates drag in the form of a bow wave, even under water in a deep pearl dive.
Cohesion and Adhesion
Water sticks to objects, this is adhesion. Water sticks to surfboards, creating a water layer that moves with a surfboard. This water layer moves independent of surrounding molecules, creating turbulence, which is drag. A surfboard pushes water at lower speeds producing adhesive surface resistance and a bow wave.
Water sticks to itself, forming puddles, lakes, seas and oceans. This is known as cohesion. Hydrogen's inter molecular bond holds water molecules together, making water viscous and resistant. Water resistance prevents a surfer from bouncing off the bottom, in a wipe out. When a surfer falls in water, he generates many little waves which radiate from his body. The falling surfer displaces water in wavelets as he sinks. A surfboard displaces water to move. At high speed water cannot be displaced fast enough and blocking speeding fast objects. Hydrodynamic resistance or lift is created.
According to renown chemist Barrett Stoller, the inter molecular Hydrogen bond is very strong. The bond is even stronger in cold temperatures, which may affect surfboard performance. The Hydrogen bond resists parting by flat speeding objects. There is very little space between water molecules, therefore; water will not compress. It actually pushes back when objects his its surface at high speed. On the other hand, you can part water by slowly moving your finger through it.
Water Cohesion Protects Surfers
When someone falls in water, they displace water by pushing it aside. As the person sinks, water moves out of his path. Sink rate or descent speed gradually decreases to zero. Water displacement cushions the fall. Water is displaced and not really compressed. in a fall with lower impact and lower descent speed, water is displaced by the gravitational force of the person's weight.
Falls from heights above two thousand feet into water, are usually fatal. At these heights objects attain terminal velocity, which is the maximum speed reached by falling objects. Due to velocity of the object, water cannot move out the way fast enough. Very little water is displaced by fast moving, objects. This causes a very hard landing.
Water Cohesion Can Increase Paddling Speed
When a surfer strokes hard, he creates a wave, with his hand and arm. This is again Wave Making Resistance. This resistance propels him forward. If he opens his fingers, he creates a larger wave, increasing resistance. Open fingers grab more water due to cohesion. Water molecules stick together to form a larger wave. This will increase thrust and add power to his stroke. When open fingers move rapidly, their wakes overlap and form a single large wake. The finger gaps are filled by the wake. When his hand moves slowly, the fingers instead, part water individually. With a slow stroke, water slips through his fingers. Higher hand speed with fingers opened generates greater resistance. This is a technique used by many Olympic swimmers.
The Foam Ball/Water Parts Water
Waves get their form, shape and size due to water cohesion. When a wave breaks, the lip impacts the base of the wave and breaks water cohesion. This creates two wakes or splashes. One wake shoots water and spray upwards in front of the wave. Another wake shoots water into the wave or barrel. The water shot into the wave, rolls in the curl. Due to the sticky properties of water, it develops into a foamy ball. This ball is called a foam ball. The foam ball can be blown out a hollow wave, with compressed air. A blast of air shoots out of the wave, when the cavern collapses.
A surfboard has rocker or nose lift, to prevent the board from penetrating the surface and submerging. Rocker has diminishing returns, too much can slow the surfboard, and too little will cause it to go underwater. Rocker forms a bow or bend on the underside of the board. When this bend is extreme, and the bottom is flat, it is exposed to contact with irregular water surfaces. At high speeds, it is vulnerable an abrupt impact, which can launch a rider. Speed is the essential factor. At lower speeds, extreme rocker with a flat bow, displaces water and surfboards continue to move. When acceleration and deceleration is gradual a flat bottom works well, absorbing impact and displacing water. The flat bottom cannot function well at high speeds in uneven water surfaces.
A misconception of modern surfboard design is, increasing rocker prevents pearling and stopping. The assumption is, a surfboard stops in a pearl because it cannot move underwater. This is only partially true. When the nose goes under water, pressure on the top of the board comes from the surfer’s weight and gravity forces, not water. Water over the top is shadowed by the rocker and spills over in rolling eddies. Top pressure from water is not a factor, unless the board goes very deep. Surfboards stop in a poke because the flat bow pushes water. A flat bow pushes water forward, before it is directed around the board. At high speeds, water immediately accumulates ahead of the board, creating a wake that blocks movement. The board abruptly stops and the rider is catapulted. The flat board exhausts kinetic energy. A displacement shape uses kinetic energy to push water out of a surfboard's path.
When rocker is increased by designers, it increases the protruding bend in the bow. The bow pushes water out of the rider's path, so the board can move forward. The amount of water that must be displaced increases with speed. At higher speeds a flat bow pushes water forward, building a bow wave that blocks the surfboard. Water is cohesive, molecules bond together and block a speeding surfboard. Water is unlike snow which can be pushed aside by the bend in a snowboard.