Understanding Waves

The ocean is always changing and there are various factors that give shape to waves. Great waves are miracles of nature as there are so many different factors that need to be just perfect for excellent waves to form.

Every surf spot is different, and generalising is difficult, but there are four main factors that you’ll always have to consider at every surf spot.

Swell, Wind, Tides and the Contour of the Ocean Floor / Shape of the Shoreline

As winds blow over the surface of the ocean, friction between air and water transfers energy from the wind into the ocean. This is how swell is generated.

To visualise this, take a deep breath exhale over a flat surface of water in a small container. Ripples will form. These ripples are the origin of all swell.

Generally speaking if a wind blows at a speed of 100 km/h, over a distance of 100 km, without changing direction, the swell generated would be one meter high. It is not only the strength (speed) of the wind but also its consistency that matters. In order to form swell, a wind cannot change direction erratically. If it does, the energy transferred into the ocean will be moving in different directions and there will be no continuous swell build-up.

Big swells are generated by strong winds, usually storm systems, far out in the open ocean. Sometimes thousands of kilometres from the shore. This type of swell is called ground-swell. Because the swell is bigger and formed further away, it has spent more time interacting with the ocean floor. Hence the name ‘ground’ swell.

Swell can also be formed by winds closer to shore. This type of swell is called wind-swell and it’s usually smaller and less consistent.

The names should not cause confusion, as all swell, both ground-swell and wind-swell, is ultimately formed by wind.

Swell Direction

Swell direction is vitally important because a certain spot will always produce the best waves with a certain swell direction. Some spots work on different swell directions, but there will always be an optimal scenario that is almost guaranteed to produce good waves.

As with wind, swell is named for its point of origin. An easterly swell originates from the east. To surf the best waves possible you need to know how different swell directions impact upon a particular surf spot. But there’s no formula to calculate this with. Experience and local knowledge is the only way of knowing which swell direction works best for a particular spot.

When you surf good waves, find out what kind of swell produced those waves and make a mental note. Observe the spot over time and speak to the locals.

Swell Height & Period

It’s good to know how big the waves are going to be. Some surf spots become un-surfable above a certain size while other spots need a minimum size to start producing waves.

Swell height is either measured in feet or metres and swell period in seconds. Swell height measures the height of one swell, from top to bottom, (trough to crest) while the period of a swell is the amount of time that passes between consecutive swells. These measurements come from offshore buoys and are usually given as averages.

Both these numbers are important when judging the eventual quality of waves at any particular surf spot. Swell size is relatively straight forward. A bigger swell means bigger waves.

Swell period is a little more complex.

Simply put, swell with a longer period has travelled further to reach shore. Not only that, but as swells travel through the ocean they line up. Meaning that swell with a longer period will come in long straight lines. Such organised swells travelling together in straight lines usually mean better waves.

As always, experience is key. Observe a spot over time and speak to the locals. This way you will learn to judge the eventual size of the waves based upon a simple forecast.

As explained earlier swell is generated by wind. But this happens far from shore.

A good swell however does not always guarantee good waves. Good waves require favourable local winds, the wind blowing at the surf spot where the swells break to form surfing waves.

Here a sharp distinction is made between offshore and onshore winds.

If you are standing on the beach, facing the ocean, and the wind is blowing into your face, it is an onshore wind. The wind is blowing from the ocean onto the shore. An onshore wind is almost always bad for waves. It makes the waves choppy and messy. Instead of breaking cleanly, breaking swells begin to crumble and become flat. Onshore winds blow from behind the oncoming swell thereby pushing them down.

Onshore winds aren’t too bad if you’re still learning, but for advanced surfers onshore wind is almost never favourable.

What you want is ‘clean’ surf. Clean waves are fanned by light offshore wind, or no wind at all. Offshore wind blow from the shore onto the ocean.

When the wind is offshore, or there is no wind at all, waves are smooth and without any bumps or chop, which makes for a good smooth ride. Light offshore winds, winds that blow into the oncoming waves, groom waves by lightly holding them up before they break. Light offshore winds are great for surfing!

Strong offshore winds can also easily spoil waves. Certain spots, and big strong swell, can handle a lot of offshore wind, while other spots, and small swell, cannot handle any wind at all.

Also some spots are sheltered from certain local winds, which is good if the wind would otherwise spoil the waves.

Winds that aren’t directly off- or onshore are usually referred to as cross-shore winds. This can be great for windsurfing or kite surfing, but only rarely does a cross-shore wind increase the quality of the waves for surfing. If a cross-shore wind is anything more than a light breeze, chances are it will spoil the waves somewhat.

Tides are an important factor in the perfect wave equation. The quality, speed, size and very existence of a wave will sometimes depend entirely on local tides. For this reason it is important to factor in the tide cycle to predict good waves at any particular surf spot.

Some spots work better on high tide and others on low tide. Some spots work better on a pushing tide while others work better while the tide is going out. Some spots only work on a spring low or spring high, when the moon is full or new.

It all depends on the interaction between the tidal cycle and the bottom contours of the shoreline. Again local knowledge and observation is absolutely crucial! At some spots good waves will completely disappear with a certain tide.

Basically tides affect the depth of the water. This will either hide or expose the ocean floor, and ultimately it is the ocean floor’s contours that make swells break into ridable waves.

Swells break to form ridable waves when the water through which the swell is travelling becomes too shallow to accommodate the energy of the swell.

Swells rise above the surface of the water once their energy is pushed up by the ocean floor in shallower water. Only when swells ‘break’ are ridable surfing waves formed.

As the energy of a swell is pushed further and further above the surface of the water a ‘water-structure’ is formed. These are usually visible as an unbroken swell lines travelling towards the shore. As the water gets shallower, the swell line becomes more visible as the water structure is pushed higher above the surface.

Tension starts building.

Swells ‘break’ when the built up tension becomes too much for the water structure to handle. At that moment the water structure of the swell will collapse in on itself, forming a breaking wave.

Generally swells break to form waves when they reach a depth of one-and-a-half times their own size. A two-metre swell will start breaking in three metres of water.

The shape of a wave, and the way it breaks, is largely dependent upon the contour of the ocean floor. If the water changes depth suddenly, waves will break suddenly, causing a very hollow and sometimes dangerous wave.

If the water changes depth gradually, waves will break gradually and gently. These are usually the best spots for beginners. As you gain experience you will be able to tell a lot about the ocean floor by simply looking at the waves.

The contour of the ocean floor also determines whether a wave will break left, right or all at once, which is a close-out. Swell direction can also impact this, but for the most part, if the water depth does not change at an angle, relative to the incoming swell, a wave will close-out, meaning that the entire swell will break all at the same time. This is not ideal for surfing.

To properly surf a wave down the line you need a wave that breaks a little bit a time. This will either happen from left to right or vice versa, from right to left.

Depending upon the composition of the ocean floor and the shoreline in general, surf spots can be broken down into three broad categories.

Beach Breaks

These waves break over a sandy bottom, generally within about 100 meters or less from the shoreline.

Waves at beach breaks can change overnight. It all depends on the shifting sand banks. Currents, storms, tidal effects and even man-made structures can affect sand-banks.

Beach breaks can sometimes be very fickle and inconsistent. Waves will not always break in the same place, day in and day out, because sand moves around easily. However, beach breaks are generally the safest for beginners because there are no rocks and waves break closer to shore.

That being said there are some spots where sand-banks are very consistent and capable of producing world-class waves suitable only for advanced surfers.

Reef Breaks

The ocean floor at reef breaks consist of coral reef or rock. These waves can break close to shore or very far out to sea. Whenever a reef is exposed to open ocean you have the potential for a breaking wave. Reef breaks can produce very high quality consistent waves because reefs do not move around as sand does.

Reef breaks often produce waves that are only suitable for more advanced surfers and only rarely are reef breaks good for learning.

Point Breaks

The defining characteristic of a point break is typically a headland where the coastline comes to a point. Man-made jetties can have a similar effect. Waves at point breaks break either right or left, while reef breaks and beach breaks can sometimes break in both directions. Point breaks can produce incredibly long rides.

Swells at a point break will enter into shallow water at an angle, allowing the swell to break at the point and then ‘peel-off’ towards deeper water, thus continuously breaking along the shore. On good days these waves unravel like spokes on a wheel and it can seem endless.

Point breaks can be either sand bottomed or rock bottomed, as the point break refers more to the shape of the shoreline than the composition of the ocean floor.