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Happy New Year! Responsible and Safe Fluid Dynamics

Fluid Dynamics

All vessels move in water by moving water. Surfers generate waves while riding waves. At the start of a ride a surfer generates a forward wave called a bow wave; and an aft wave known as a trailing wake.

As a surfer picks up speed, the bow wave dissipates and only a trailing wake follows. In the next video, note the bow wave that precedes a beautiful ride by Brett Barley.

In this normal progression, a board moves seamlessly The bow pushes water out of the boards path, in the form of a bow wave. The rest of the board follows until it begins to plane. Then the bow lifts out of the water. Most bows are flat, at lower speeds the flat bow moves well. At high speeds more water must be moved or displaced, especially if a boards gets airborne. The bow becomes a landing pad, due to the angle of descent and gravity. In a late takeoff with an airborne drop, a bow wave can stop movement. A flat bow with high rocker may not move enough water out of the way, fast enough to allow movement. A speeding board can get stuck behind its own wake.

Kai Lenny and Ryan Hipwood take off together at the WSL Peahi Challenge. The bow wave is indicated by the red arrow. Water displaced covers Ryan, but it is not enough

water displacement to keep the board moving.

A flat bottom pushes water forward, then around the board. Water accumulates at the bow, creating a bow wave directly in the rider's path. Note how Kai's board planes in the flatter part of the wave. Lower rocker can plane through water with less resistance. Water is diverted around Kai's board.

Kai's GoPro captures a rare picture of a bow wave under Ryan's surfboard. This bow wave abruptly stops movement, Ryan cannot remain standing. Only the board stops, Ryan continues through the air. High rocker can displace more water, if the bow is round or Vee'd like boat hulls. The ride can progress further, as water is moved out of the board's path.

Safe surfing into the new year.

Videos and pictures from Youtube. Peahi Challenge presented by WSL.

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