WSL Quiksilver Pro France
What really happens in a nose poke? A nose poke is a shallow pearl dive. The nose or tip of the surfboard may or may not submerge underwater. The surfboard usually decelerates. At high speed the board can stop abruptly and launch the rider. A surfer can control and ride through a gradual deceleration as Kanoa demonstrates in the following sequence.
Deceleration is caused by nose rocker. The underside of the surfboard's nose bend creates a bow. The bow pushes water out of the rider's path, so the board can move forward. The water displaced is called a bow wave. The bow wave is not visible, but; it sprays water over the nose of the board and against Kanoa's forward leg. Water shooting over the top of the board does not create drag. Water shoots over the board in an eddy, even when the board goes under water. Downward force is generated by the surfer's weight, not water.
Three vectors in the photo above depict the gravitational forces at work. The vectors depict a typical inclined plane, physics analysis. The left vector is perpendicular to the board, known as the normal vector. The right is perpendicular to the horizon, and bottom vector is parallel to the surfboard plane. The right vector is the weight vector, its force increases with steepness. The force in the bottom parallel vector represents net force or acceleration. This value equates to motion when resistance or friction is low. In this ride, the bow is efficiently moving water around board, reducing resistance.
Gravitational forces can be calculated with geometry and trigonometry. Weight and mass are a function of gravitational force. It is not necessary to do the calculation in this case. The surfer's weight is a factor driving gravitational force in a nose poke. The gravitational force creates the bow wave which causes deceleration, by resistance and friction. The belief that water over a submerged nose causes drag in a nose poke, is a misconception. Water over the top effects only a very deep pearl. The misconception resulted in higher and higher nose rocker, which creates more bow resistance or friction.
This poke takes Kanoa in the opposite direction away from a close out section that lays ahead. Kanoa cannot get back on track until the nose is free. This may have caused him to meet the on coming section a little late. A slight correction may make a large difference.
Kanoa does at least three nose pokes in this heat. This is a testament to vertical surfing. Progressive surfing has pushed the limits of a flat bow and high nose rocker. Kanoa misses advancing by 0.55 points. The last nose poke occurs at higher speed. The amount of water displaced is dependent on speed. The faster a flat bow board moves the less water it displaces, however; more water displacement is required to keep it moving. The board hits a wave face or bottom with high impact. The bow must push water out of the board's way rapidly or it will stop. At high speed, water's cohesive force resists displacement and stops the board. The force is hydro dynamic lift, the same lift that supports a surfboard on a plane. Hydro dynamic force also keeps surfers from hitting bottom in a fall.
Kanoa breaks his fins free and free falls into the wave with good speed.
A fast moving surfboard can impact water with high gravitational force. Water cohesion resists high impact due to the inter molecular bond of hydrogen atoms. A flat bow pushes water forward and downward before guiding it around the board. Water displacement is not fast enough to allow a speeding surfboard to continue moving. The bow wave spray covers the nose of Kanoa's surfboard nose.
Alternative bottom shapes either round or vee parts water and moves it out of the rider's path. A speeding surfboard can continue to move after a slight deceleration. Alternative shapes can cushion a high impact and prevent abrupt deceleration. Lastly, reducing nose rocker may increase performance.
Photos and video from WSL Quiksilver Pro France,Heat Analyzer, You Tube