An Epic Ride Viewed from Kai's Go Pro WSL Peahi Challenge/ The Bow Wave

November 15, 2017

 Revisiting an epic ride.  Kai Lenny and Ryan Hipwood take off together under the lip in the WSL Peahi Challenge Final, for an exciting and daring escapade.

 

Fluid Dynamics

A vessel moves in water by moving or displacing water.  Surfers create waves when they ride waves.   At lower speeds they generate a trailing wave, well as a forward wake or bow wave.  As speed increases the bow rises and the forward wake dissipates.  The trailing wake is usually very visible as a trail of spray.  Forward wakes are rarely visible in surfing, because water contact occurs under the board, at the bow.  Spray from the bow wave is sometimes visible and indicated by red arrows.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Wave Making Resistance: The Bow Wave

Vessels use energy to push water out of a hull's path, creating waves.  Water builds ahead of a vessel forming a wave, known as wave making resistance.  In heavy seas, ships and boats are designed to part swells and chop, to lessen the discomfort to passengers.  Vee or round hulls and lower speeds prevent injury from being tossed about the ship.  A surfboard, like a boat will pitch its rider with extreme fluctuating speed and pitch.  A surfboard planes with its bow out of the water.  It planes more like a speed boat than a  sailboat or ship.   If a surfer can keep the bow above water, he will avoid creating a bow wave during the faster phases of his ride.  A surfer is controlled by gravity in a free fall, and he cannot fully control a landing.  Often a surfer leaves the wave and lands on the bow with hard impact.  Most surfboard bows are flat and do not cushion impact or part water.  A surfer cannot remain standing in a hard flat landing.  A flat landing creates a splash or a bow wave.  The bow wave is resistance that can abruptly stop a surfboard.  For more on gravity force see links on right of this page.

 

 

Ryan's surfboard does not submerge.  The bow or underside nose rocker bend, makes heavy impact with the wave face.

 Spray from the initial induced bow wave shoots over Ryan's legs and waist.  More spray is visible coming out from under the board.  Water is streaming rapidly up the wave's face, compounding resistance.

 Ryan's board continues to push water, as spray is still visible over the nose of his board.

In a rare photo, a bow wave is visible under Ryan's board.  Bow waves are usually not so evident.   His board is rapidly decelerating and Ryan is beginning lift off. 

 

 

The Camera lens distorts Ryan's angle of descent, but captures a good image of a bow wave.

 

 

 

 

 

Only the board stops, Ryan continues through the air with his kinetic energy.  It takes less resistance to only stop a surfboard.   A comparison would be to trip runner by his foot, as opposed to wrestling down his speeding body.  A surfer cannot remain standing when his surfboard stops abruptly, it is as though someone tripped his foot.  To successfully survive a nose poke, a board must keep moving as Kai's surfboard does.  Impact with water must be cushioned and parted by the bow.  For more on this subject, see the earlier posts in the menu to the right of this page.

 

Conclusion

More nose rocker generates more wave making resistance.  Extreme nose rocker requires a softer vee or round bow to avoid stopping on impact.  A flat bow and high nose rocker resists parting water at high speed, due to water cohesion and hydrodynamic resistance.  Flat bows are designed to ride on the surface and cannot displace water efficiently.  Water must move rapidly out of a speeding boards path or it will stop movement.  Kai's board has excellent rocker and riding it, Kai turns in an outstanding performance.  Watch him surf out of nose pokes and ride very deep in dangerous giant waves.  Note also the jet ski in the opening of the video.  It noses in and stops.  Demonstrating how water stops vessels at high speed with high impact.

 

 

 Photos and video from YouTube, WSL Peahi Challenge

 

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