Introduction

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Page 47

The sport of surf-riding is only made possible by the characteristic behaviour of waves upon gently sloping beaches.
I hope that those who have enjoyed this activity, and can perhaps practice it with the skill shown on Plate 50, will not think me
too prosaic if I describe some of the scientific principles on which it is based.
For a successful surf-ride up a beach it is essential that the board should travel at the same speed as the advancing wave, and also be kept stable so that it resists the tendency to broach to.
The first of these requirements is met by choosing a wave that is just beginning to break, so that the forward movement of the water particles in the crest is almost as great as the speed of the wave itself.
The balance of speed is made up by movement of the board through the water, this being due to the fact that it is perpetually sliding 'downhill'.
The second requirement must be provided by the surf-rider.
As we have seen, the water particles in the crest are advancing

Page 48

more rapidly than in any other part of the wave.
Therefore the velocity of the front edge of the surf-board is higher relative to the water than the velocity of the back.
This means that the slightest deviation in the direction of the board must cause it to slew round parallel to the advancing crest. It is the surf-rider's job to counteract any such tendency by moving the weight of his body to left or right as required.
Surf-riding is thus seen to be a beautiful example of a most delicately balanced interplay of forces, relying for its main motive power on the tremendous vitality of the sea itself.

Facing page 48 5a. Surf-riding at Bondi Beach, Sydney, Australia. The sport demonstrates a principle of wave mechanics (see p. 47)

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Carrington, Richard: A Biography of the Sea; The story of the world ocean, its animal and plant populations, and its influence on human history... Basic Books, New York, 1960. Hathi Trust https://hdl.handle.net/2027/uc1.31822013446349

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