The Magic of Wave Power

You often hear surfers talking about waves sometimes feeling more ‘powerful’. Is this really true? Absolutely. It all has to do with basic wave physics. There are three basic points to understand about ocean waves. First, it’s important to know that the movement of energy and water in a wave is different. In deep water, water particles move back and forth underneath waves in orbital motions, but the water doesn’t really go anywhere. Water only starts moving towards the beach once waves enter shallow water, slow down and then break. What gives waves their shape is the energy moving through the water, just like the motion of sound or light (or Mexican) waves through the air. Second, there is an exponential relationship between the height of the wave and the amount of energy that waves have. So at any given point on the ocean, bigger waves have more energy and even bigger waves have a lot more energy. Third, the speed that waves are travelling is related to the wave period – the time it takes for two wave crests to pass the same point. The longer the wave period, the faster the waves travel.

Wave power is the rate that wave energy is moving and is basically equal to the energy of the wave multiplied by the wave speed. This means that bigger waves will have more power, but so will longer waves that are not necessarily that big. Typical swell wave periods on our coast are between 8 to 10 seconds, but sometimes we can get a clean ground swell that has travelled from a very distant source that has periods of 12 to 14 seconds. This is similar to what you get in Hawai’i, which is renowned for its powerful waves.

The Hawaiian islands sit in the middle of the Pacific. Pretty much every swell wave that reaches Hawai’i has travelled a long distance and has a long wave period – and therefore more power. I remember the first time I bodysurfed in Hawai’i (Slaughterhouse Beach in Maui). The waves didn’t look any different in height to a fairly typical day here, but the second I caught the wave, my eyes almost popped out of their sockets in surprise, because it was like riding a rocket. I could not believe how fast and heavy it was. It was the same deal several years later when I went boogie boarding on the Banzai Pipeline on Oahu’s North Shore. It was summer there and the waves were only about 1 foot, but they still packed a wallop. So wave power is definitely real, especially when wave periods start getting longer than 12 seconds. Give it a go to feel the power yourself!

Beautiful lines of long period swell at Byron Bay, NSW, Australia (Photo R. Brander)