Often at Sways, surfboard performance is conveyed relative to the motion of water in a wave. The animation below is useful for visualizing that movement of water – watch the yellow dots.
The water in an ocean wave moves in a circle (up and down, back and forth). The center of that circle remains stationary. Only the waveform itself continues to move forward in the horizontal plane, towards the shore. However, the surfer/surfboard moves in both planes, horizontally over the water surface towards the shore and vertically up and down on the wave face. When the surfer is executing a bottom turn in "the flats" in front of the wave, there is no significant vertical or horizontal water movement -- only the surfer/surfboard are moving.
On the wave face, there is an upward water motion vector in the vertical plane. The waveform -- not the water -- has a continuous horizontal motion vector toward shore. The surfboard is propelled forward/horizontally by gravity and the slope of the waveform face; in front of the waveform, sliding over the surface.
Wave animation link:
There can be significant horizontal flow in the “flats” in smaller waves, typically reefs with shelfs.
The answer to most of your questions is: It depends.
It depends on the board, or the rider, or their position and orientation on the wave, or the wave… Or any combination of those.
I do my best to consider relevant dynamics.
Most do not ride Teahupoo.
It seems some get fixated on the updraft motion of waves.
The horizontal, gravity propelled vector/plane is important and frequently ignored. Is there a critical slope/angle for the board to slide due to gravitational acceleration? Critical take-off velocity? Does the face slope/angle have to be steep enough for gravitational acceleration to overcome the upward movement of water (affected by board size, rider mass, paddling velocity)?
In the flats, which has greater impact? Horizontal surface velocity and momentum of the surfer/surfboard or the intitiation/start of upward water motion in the wave face? When and where does this motion start?
Does the velocity of the water moving up the wave face have greater effect than gravitational acceleration or the centripetal accleration produced by a bottom turn/cutback? Is greater centripetal acceleration required for a cutback at the top/crest vs. the trough – turning into vs. with the updraft?
In the horizontal plane, is water flowing over the bottom and rails of the board. Or are the board surfaces moving over and through the water? Relativity and frames of reference?
What causes the wave amplitude to increase in shallow water and the crest to fall? What causes the crest to de-stabilize? Does the wavelength decrease? Is wave motion linear or non-linear? How does this affect kinetic energy?
What you need to consider now is how the velocities of the particles change relative to each other as the wave breaks, and the circular pattern distorts.
First, I am glad you are beginning to consider the correct motion, your musings will become less contradictory as you come to terms with the reality of the way the water moves.
A few things…
- At certain breaks there is significant backward movement of water at the trough. At others much less. Your bottom turn statement is false.
- The circular patten changes when the wave starts to break, and the forward motion of the water can become significant. The circular path is broken.
- When the rider is in trim, the water is mostly moving up. Trim is a state of balance where the riders weight is countered by the force of the moving water acting upon the fins and hull, and their interaction. (I know this third point doesn’t directly relate to your statements here, just others previously).
