It’s an imaginary line in the face of the wave that corresponds to the ideal trajectory for a surfer wishing to exploit the wave’s kinetic potential: this spot under the lip at the level of the wave’s upper third enables the surfer to maintain maximum speed, with no need for any motor action other than a minimum of weight on the front leg. This is the point of the wave that offers the most velocity.
It’s also the trajectory of a surfer in the tube, or of a longboarder on the front of his board (hang five).
It is around this invisible line that the surfer will constantly evolve, executing descents and ascents in the trough of the wave.
So a surfer who stays in the lower third of the wave will invariably end up slowing down and being caught by the breaker, thus losing the wave. Unless it’s a deliberate braking manoeuvre to get into the tube.
On the contrary, the surfer who stays on this line will succeed in surfing a regular wave along the whole length of his breaker, from the bottom to the edge.
