Hollow and mellow wave

Wave Calculator reprise- Hollow vs Mellow

Calculation is Fun!

Last week I showed how to use the Wave Calculator to calculate the volume of water that moves between the wave trough and the crest. Actually it can do a bit more: the Surf Wave Calculator, can help for understanding breaking wave dynamics. I want to make an estimation of the wave breaking at Popoyo given a swell of 2m@18sec.

Let’s go through the calculation. Open the Wave Calculator and go to the Surf Wave Calculator; enter the following parameters: 2m height, 18 sec period and 100 m depth. Plus, enter 20° as angle of incidence and select “Gravel” as Sediment type, which simulates a reef break.

2m@18sec breaking on gravel bottom

As you can seey you will get a breaking wave height of 2.87 m. The wave breaking type is “Plunging” (which means “barreling”), in this case the energy of the wave is released in very short time. The wave will break at a depth of 3.56m, which can be considered “safe” to avoid hitting the bottom, in case of wipe out.

Let’s see what happens leaving everything unchanged but the period and sediment type: enter 9 sec and “Coarse Sand” as Sediment type. This could be the case of a wave breaking on a mediterranean beach break:

2m@9sec breaking on a coarse sand bottom

You can see that the breaking wave height reduces to only 2.05 m. Moreover, the breaking type is different: the 18 sec wave will produce a plunging breaking that is much more intense than the spilling breaking of the 9 sec wave. The wave will break at a depth of 3.12m, which can be considered still a safe value. The estimation of how much water you get on your head is fairly difficult to determine though.

To get a more scientific approach about the topic I recommend to read one of our old posts: Why do waves break?


Most of experienced surfers can tell the power of a breaking wave just watching from the shore. Even though some waves can hide tracherous threats, like heavy hold downs or unexpected rocks lying below the surface. That’s why become so important the knowledge of the spot. Many beginners challenge themselves on conditions that are out of their abilities because they are unaware of the surroundings. Being ignorant about the rips, undertow, rocks, tide and other variables can turn a good surfing session into a dramatic experience or worse.

Mellow vs Hollow

Hollow Wave

Rider: Jeffrey Ault charging somewhere in Mexico – Photo credits: Delfim Anjos

Personally I have a passion for hollow waves, not only because they give me strong feeling and beatings.. I also prefer the wipe out on a hollow wave rather being washed by a spilling wave. The plunging wave exhausts its energy quicker, so, how to say, the beating is stronger and also shorter. Normally the hazard of wipe out is related with hitting the bottom with all consequences that can follow (breaking bones, twisting limbs, bruises, shoulders dislocation, cuts etc.). The safest area of a hollow wave is inside its pocket, in the barrell. The most dangerous is the impact zone of the lip falling down on flat water. On a large barrelling wave that area is extremely dangerous: an heavy lip closing down can make serious damage to human body and easily snap any board.

mellow wave

Rider: Jeffrey Ault Photo credits: Chris Schmitt

Spilling wave are normally easier to surf. However when the size starts to matter I experienced a couple of bad hold downs that made me rethink about mellow waves. A large mellow wave indeed can be able to drag the surfer much longer than a hollow wave, because it exhausts its energy little by little while moving from the breaking zone to the shoreline. The good news is that when the wave lets you go, you are normally far from the breaking zone. The next wave coming on you will have much less energy and you can easily back up to the beach.

I wanted to express my opinion about mellow/hollow waves. I didn’t want absolutely to say that one kind is more fun than another one. The best wave on planet is the one that gives you more satisfaction, able to evoke great memories and epic sessions. So there are a lot of great waves around. Wish you to enjoy your favorite wave this week. See you in 7 days, cheers!


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