We are proud to show you the latest video portraying some aspects of “Surfing Medicine”.
Our gratitude to all supporters, contributors, partners, surf med pioneers worldwide, our crew, mother nature, the ocean and the whole surfing community. Keep the surfer healthy and safe!
“As the world’s largest and leading collective of medical professionals in surfing the European Association of Surfing Doctors (EASD) is actively contributing to and defining standards for surfer welfare. By connecting health professionals representing all medical specialties with a passion for surfing and the ocean, the EASD seeks to share knowledge, expertise, and experience with the global surf community. In a fast developing global surf community, the EASD’s quest is to “Keep the surfer healthy and safe” through numerous activities, such as: treatment in day-to-day practice, serving as contest medical personnel in both professional and amateur surfing arenas, delivering training courses for medical lays and health professionals alike (Surf Life Support™), conducting scientific research work and publication, defining evidence-based standards within the specialty and the sport at large, and convening the Annual Conference in Surfing Medicine where health professional from all over the world convene. Share the passion? See you on one of the various EASD events and in the water!”
We are proud to show you the latest video portraying the Advanced Surf Life Support™ course. Hit the play button and dive into this challenging, teaching and fun 7-day-course:
The Advanced Surf Life Support™ course features a wide array of topics, such as rescue techniques, drowning and hypothermia, diagnosis and treatment of wounds, rips and currents to name but a few aspects. Developed by the European Association of Surfing Doctors and refined over the years it is the original and leading course in surfing medicine specifically designed for health professionals. Participants will experience theoretical and practical training as-well as land and water based scenarios by experienced surfing doctors, wilderness medics, drowning specialists, and professional surf-lifeguard instructors. YOU can make a difference – are you ready?
In the never ending EASD quest for unique knowledge and experience in surfing medicine, we connect state of art sciences. This effort is a key step to the EASD product development program, based on medical and scientific knowledge.
The global surfing community has so many talented people. Right across this community we find unique characters, supporting the EASD. We call these special persons “The EASD Scouts”. They are neither MDs nor Allied Health Professionals (AHP), but they are professionals in other topics, like physics for instance.
It is our pleasure to present the second article from our fellow scientist, physicist, and author Chris Woodford, who has worked out an interesting article for scientific and non-scientific viewers explaining the energy and power in the waves we love to ride. In doing so he has touched a medical topic related to surfing, Trauma. Trauma will also be one of the topics at The EASD Conference 2015 in Anglet/Biarritz, leading to great discussion and knowledge exchange. The international scientific effort on surf trauma is progressing. We are excited to hear more state of the art knowledge on this topic from our vast community of Surfing Doctors at the coming Conference from the 29th Septembers until the 2nd of October 2015 in Pays Basque, France.
See you in the water,
O. Markovic
EASD Board Member | Outreach, Sponsorship, Education
Blame the Sun. When you fail to take off or painfully wipe out. When you wake up the day after a stunning surf, horribly aware of muscles you’ve not seen since med school. When (much less luckily) you strain your back or break your leg and have to spend gloomy days or weeks watching from the shore. Blame the Sun for all your surfing-related problems—because that giant nuclear fireball, 150 million km (93 million miles) away, is surely to blame.
Like almost everything else on Earth, surfing is solar-powered: the energy that shoots you over the sea comes indirectly from the Sun. And what a lot of energy beams our way: theoretically, up to 1000 watts of solar power per square metre of land.[1] But the interesting thing is not where this energy comes from, but where it goes. Earth’s lopsided tilt means the planet cooks unevenly in sunlight, like a spit-roasting joint we’ve stupidly propped at the wrong angle. The tropical bits can blacken and char to the point of forest fires while the polar caps (for now, at least) stay locked in ice. Because energy likes to even itself out, Earth has a turbulent atmosphere and an equally dynamic ocean. And where the howling winds meets the tumbling water, we get waves. Lots of waves.
Credit: Waves: Woodcut by Konen Uehara (1878-1940), courtesy of US Library of Congress, Japanese Prints and Drawings Collection (public domain).
What are waves anyway?
You know the answer to this question both in theory and in practice. In theory, because you can still remember flipping through the pages of your old school textbook: amplitude, wavelength, and frequency—those are officially the measure of waves. Now you’re older and a surfer, and you spend a significant part of your life bouncing up and down the sea surface, waves mean something different: breaking waves make your day. They’re no longer two-dimensional scientific abstractions—wiggly black lines drawn on white paper—but colourful, three-dimensional memories, vividly tied to places and times, burned in your memory till the day you die. Every science book explains waves the same way: as energy in motion, shooting from place to place while the medium (water, air, or whatever it might be) goes nowhere. But every surfer—even every beach-bound wave watcher—knows better than to reduce practical waves to a simple theory. Because, in glorious surfing reality, every wave is slightly different from every other wave that has ever broken in exactly the same place.
The waves surfers care about happen at the interface between the atmosphere and oceans, although they’re not the only waves you’ll find in either the air or the water. High above your head, there are waves shooting through the sky; that’s one of the reasons you’ll sometimes see cool, repetitive patterns formed in clouds (instead of the random lumpy cotton-wool you might be used to).[2] There are also waves that travel deep underwater, never breaking the surface, never kissing the board of a single surfer, but—intriguingly—often visible from high up in space.[3]
How do waves form?
We all know the simple answer is “when the wind blows across the sea”, so the energy that was in the air is systematically transferred to the water. But how does that transfer take place? Is it like slowly running a knife over butter, when that nasty, yellow, artery-clogging fat magically springs into a curl? Is it like stirring a cup of coffee, except with friction from the wind dragging the water surface and tugging it along? Or brushing leaves off a garden path, where you slowly heap the water into a pile? It’s not hard to think of all kinds of ways the wind might stir up the water—but what does the science say?
Credit: Wind makes waves, so it’s no surprise that the biggest waves are in the windiest places. This image of wave heights around the world was snapped from space by the TOPEX/Poseidon satellite in 1992. The red and yellow areas show that wave hotspots occur in places like the Roaring Forties where the winds are strongest. Photo courtesy of NASA Jet Propulsion Laboratory (public domain).
Imagine the surface of the ocean is flat and glassy with not a wave in sight. Peer close enough and the water-air interface you see is no different from the mirror surface of a pond, where cunning insects float and scamper on invisible skin. Water has surface tension, just like a drum, and if you deform it slightly, the pulling force between neighbouring water molecules will spring it rapidly back again. Closely related to capillary action (the power that pumps water up trees or blood through capillaries), this is the first key bit of science in a glorious sequence of events that builds the waves for surfing. Because as the wind starts to blow over water, it creates minuscule ripples called capillary waves, barely a millimeter high. The water’s own elasticity—surface tension—tries to destroy them immediately by tugging them back into place.
But with a steady wind blowing, it’s already too late: the water surface is roughening up. Now friction kicks in and the wind can get more of a grip, systematically building up the ripples to make wind chop and swell that will eventually clean itself up into perfectly formed surf in a voyage that could last hundreds or thousands of miles. Once waves grow beyond capillary size, surface tension can’t stop them. Now they’re at the mercy of the most persuasive long-range force in the Universe: gravity. Where surface tension does its best to rid the ocean of puny capillary waves, gravity is responsible for wrecking every surfer’s fun by cleaning away the bigger waves: it’s the force that determines the life and death of every ocean wave as it constantly tries to smooth out the sea.
Waves without wind
Ocean waves happen when there’s a big enough input of energy to deform the water surface. Water’s dense and heavy stuff, don’t forget: a mere litre weighs a kilogram. Lifting a wave’s worth of water a metre in the air, across the entire width of that wave requires a massive input of energy and force (we’ll do some simple calculations on that in a moment). Wind supplies the energy slowly and systematically and if you’ve got something like a hurricane to hand, feeding energy to the waves over days or weeks, you can certainly lift enough water and accelerate it fast enough to generate some spectacular swell.
Credit: Pacific nuclear tests were a particularly unnatural way of making waves without wind. In 1946, as part of Operation Crossroads, the Baker Test at Bikini Atoll detonated a nuclear bomb 27m (90ft) underwater, producing a giant water column powerful enough to sink the USS Arkansas. Watercolour by war artist Grant Powers courtesy of US Naval History and Heritage Command (public domain).
But that’s not the only way to make waves. Tsunamis, usually set in motion by underwater earthquakes, cause what used to be called tidal waves by adding vast amounts of energy to the ocean in a matter of seconds. The water surface is dramatically deformed; gravity tries to restore it—and that process gives an outward transport of energy we see in waves. Explosions at sea can make smaller tsunamis. In December 1917, an accidental detonation onboard an armaments ship in the harbour at Halifax, Nova Scotia thundered out what was then the world’s biggest explosion (3000 tons of TNT), rumbling 10m-high (30ft) waves out across the sea. The atomic bomb tests that happened in the Pacific, between the end of World War II and the early 1960s, were thousands of times more powerful (equivalent to megatons of TNT).[4]
The biggest waves ever recorded on Earth have been caused not by hurricanes, tsunamis, or nuclear bombs but by rocks impacting the sea. In 1957, a giant rock-fall at Lituya Bay, Alaska dumped an estimated 90 million tons of cliff into the sea, creating waves accurately measured (from marks left on the land) to be an astonishing 530m (1750ft) high. According to geologists, the biggest wave that’s ever happened on Earth was caused by a meteorite smashing into the ocean around 65 million years ago, producing the world’s most impossibly unsurfable wave, a staggering 914m (3000ft) high (over twice as tall as the Empire State Building). Try that for size, Kelly Slater! [5]
A swell party
If you’ve ever played at making surf in your bored, Sunday afternoon bath-tub, by flipping your hand back and forth in the water, you’ll have figured out that there are three ways to make bigger waves: you can flip your hand faster, further, or for longer. The wind in a storm zone works exactly the same way when it’s making waves. If it blows faster, longer, or over a greater distance (technically called the fetch), it creates bigger waves. Why? Because bigger waves need more energy to create them (you have to lift more water up against the force of gravity, for one thing) and a faster wind blowing for longer, or over a bigger area of sea, is the way to get that energy into the water. That’s one key reason why open coastlines are so much better for surfing. The best surfing in England happens on the exposed north coast of Cornwall and Devon, in places like Newquay and Croyde, because wind-borne waves arriving there have had an opportunity to build power and clean themselves up as they thunder across the Atlantic: the fetch is much greater. On the South Coast of England, the fetch is limited to the relatively puny distance between England and France so the waves are rarely so good. The simple rule is that it takes energy, time, and distance to make great surf. The 6m (20ft) waves that delighted southern California’s surfers in August 2014, courtesy of Hurricane Marie, had had 1300km (800 miles) to get their act together.[6]
That begs another interesting question: just how big can waves ever be? If a hurricane blew for weeks or months over a long enough fetch of open water, would we get ridiculously big waves? “Yes” is the simple answer, but there’s still a scientific limit to how much waves can grow. Like houses of cards, waves are unstable structures that gravity is determined to collapse, sooner or later—with the added complication that they’re moving in the turbulent interface between the atmosphere and the ocean. Seven decades of oceanographic research has determined that waves don’t build beyond a certain steepness: the ratio of their length (measured between one wave crest and the one following behind) to their height (measured from crest to trough, or maximum to minimum) can never be more than seven to one. Waves break on the shore when the rising slope of the beach (or reef) increases their steepness beyond that critical ratio; out in the open ocean, the same limit applies, and we get white horses (white caps) forming as gravity forces excessively steep waves into premature collapse.
In practice, when the wind blows across the water in a perfect-surf-creating storm, we reach an equilibrium. The wind keeps on adding more energy to the water, but the waves keep collapsing. At this point, we have what the oceanographers call a fully developed sea. The waves are as big as they’re ever going to get. All they have to do now is get themselves to the shore, where the surfers are waiting.
Artwork: Skill in the Surf, published in February 1945, was one of the world’s first surfing manuals—aimed at troops “surfing” to the shore in landing boats. You can read the fascinating document in its entirety courtesy of the The Naval History and Heritage Command (public domain). Most interesting to surfers is Chapter 1X, Where the Sea Meets Land, which describes the tactics of making a military landing through surf.
The birth of surf science
Surfing is essentially a 20th-century invention, and so is surf science. But who first had the idea to turn the wonder of waves into a scribble of maths—and why?
Just as the wetsuits I explored in our previous article were essentially a Navy invention, so surf science owed its birth to military manoeuvres. As Stephanie Pain recounts in a fascinating popular science book called Farmer Buckley’s Exploding Trousers: And Other Odd Events on the Way to Scientific Discovery,[7] the pioneers of surf forecasting, Norwegian oceanographer Harald Sverdrup (head of the famous Scripps Institution) and his young American student Walter Munk, figured out how to predict wave heights from the wind speed, fetch, and duration while working for the US military during World War II. Fortunately, they also had loads of data to test their theory and quickly honed their equations enough to make accurate predictions. Although no-one knew it at the time, this crucial work was used by the Allied forces to select the best days for the famous beach landings. It was first used to pick a calm day for an assault on North Africa on 8 November 1942 and, subsequently, for the D-Day landings in Europe in June 1944. Surfing science, in other words, changed history.
Sverdrup and Munk completed their work in 1943, but it remained classified until after the War, finally appearing in March 1947 as US Navy Hydrographic Office Publication Number 601, “Wind, Sea, and Swell: Theory of Relations for Forecasting”. Later refined and extended by Charles Bretschneider, the revised theory became known as the SMB (Sverdrup, Munk, Bretschneider) model. Though it’s only a basic explanation of how wind makes waves, it’s still widely referred to today, especially in simpler articles like this, but it’s now been superseded by decades of more detailed research. If you’re interested, check out the more detailed explanation in Tony Butt’s excellent Surf Science book (see Further Reading below).
How much energy is there in waves?
That’s a fascinating question with all sorts of answers, ranging from the dreamily poetic (like the Japanese woodcut that opens this article) to the studiously scientific. It’s worth quantifying the energy in waves for all kinds of practical reasons. From an environmental point of view, it tells us how feasible it is to build things like renewable wave-energy systems—and whether we can harvest more energy from the hidden heat in ocean water (the temperature difference between the ocean surface and its depths) than from its mechanical energy (the back-and-forth, up-and-down movement of water caused by tides and waves). From a surfing point of view, asking this question tells us exactly which waves are rideable and what you can do on them. Everyone knows you can’t catch a small wave on a surfboard (or even a boogie board)—and the simple scientific reason for that is that a rideable wave needs to contain a minimum amount of energy to lift your body against the force of gravity and accelerate you to its own speed.
It’s also interesting to ask the question from a medical-physics point of view: the force that breaks a surfer’s bones or mashes her muscles comes from the energy hidden in a wave. Is there really enough energy in a typical wave to do that much damage?
Go figure
Let’s try to guess-timate how much energy there is in a medium-sized wave crashing down on top of us as we stand in the surf. I must emphasize that this is “back-of-the-envelope” physics and not in any sense rigorous or correct oceanography. It’s what’s technically referred to as “just a bit of fun”! I’m not going to attempt to use the complex equations that are really needed to do this properly, but if you want to have a go, I’ve given some pointers in the references down below.[8] For now, let’s see how far we can get with the kind of basic science we learn at school.
We know the total energy is the sum of the wave’s kinetic energy (because the water is moving) and potential energy (because the crest is lifted up above the mean water level). Let’s not get too bogged down, though: let’s simplify everything as much as we can to the point of basic, school-level physics.
Suppose we have a 1m width of a wave that closes out completely, with the water coming to an impossible, screeching halt (so effectively it loses all its kinetic and potential energy when it breaks). According to Willard Bascom (one of the founding fathers of surf science), the speed of a decent surfing wave is about 40 km/h (25mph or 11 m/s).[9] For easy sums, let’s assume the wavelength (the distance between one wave peak and the next one) is 2m and the amplitude (the height of the wave) is also 2m, so the volume of water above the mean sea level that we’re interested in (the dark grey bit in the figure I’ve drawn here) is roughly 1 x 1 x 0.6 = 0.6m3 = 600 litres, which weighs about 600kg. Simplifying very greatly indeed (I know, I know… but bear with me), that gives us potential energy of mgh = 600 x 10 x 1 = 6000 joules and kinetic energy of ½mv2 = 300 x 11 x 11 = 37,000 joules, making a grand total of about 43,000 joules—or call it 50 kilojoules to keep things simple. This is a rough estimate of how much useful (non-heat) energy there is per metre of a simple breaking wave—and the actual value is likely to be less than this because of all the simplifications I made (a real wave isn’t this steep; it doesn’t stop completely when it breaks; it has an ever-changing, irregular volume; its total mass is not all concentrated at exactly the same height; and so on—this is back-of-envelope, guerilla physics!). Remember that this is the energy in a single meter width of water—so a stupendous wave shattering into sand across 1km (0.6 miles) of a bay could theoretically deliver 1000 times more energy than that: a wave like that breaking each second could theoretically make 50 megawatts of power (equal to about 25 very large wind turbines).
How accurate is my guesstimate? I’ve seen a few textbook estimates of the energy in waves that run between 10–100 megawatts per kilometre of shoreline [10], so even if my assumptions and calculations are extremely rough and ready, my final figure isn’t too bad. Shore-mounted wave energy harvesting devices (which work by using the wave’s energy to push a column of air back and forth past a turbine, making what’s called an oscillating water column or OWC) also quote figures roughly in this ballpark. The LIMPET wave energy harvester in Islay, Scotland can make a maximum of 500 kilowatts; a similar water column generator that operated in Toftestallen, Norway in the late 1980s managed 1 megawatt for three years until storm waves smashed it to pieces.[11]
Credit: Except for the energy you provide with your own muscles, everything you can do on a wave is determined by the energy that wave picked up on its way across the ocean. Photo of the Red Bull Rivals International Surf Competition, 2014, by Sgt. Derrick K. Irions courtesy of US Marine Corps (public domain).
Catching waves
Do the numbers tell us anything useful? Suppose you weigh 70kg (not including the weight of your board). If you want to travel at 40km/h (11m/s), you need kinetic energy of ½mv2 = 35 x 11 x 11 = 4235 joules. To ride a meter above the ocean surface, you’ll also need potential energy of mgh = 70 x 10 x 1 = 700 joules, so you’ll need about 5000 joules of energy altogether. Let’s say it takes you 5 seconds to catch the wave. The power your muscles and the wave need to supply for you to start surfing is the total energy needed divided by the time it takes, so that makes an average power of about 1000 watts to reach 5000 joules in 5 seconds—as much as a typical clothes washing machine. Could you get that from a 1m wave? Maybe yes, maybe no. My estimate of about 50 kilojoules was for the total energy in 1m width of a wave, which sounds like it’s 10 times more than enough—but, remember, you wouldn’t get all that energy from the wave (it keeps moving and doesn’t break) and you’re not tapping into a 1m width of water (maybe only the width of your board).
Kids, lucky things, can catch smaller waves than adults because they weigh about half as much and they can accelerate faster. The potential and kinetic energy of a surfer are both linearly related to body mass, so if you have less mass, you need correspondingly less energy—making it more likely the wave will sweep you along. By the same token, if a wave is big enough, you can (theoretically) surf it in or on whatever you like. Willard Bascom’s classic book Waves and Beaches has an amazing photo of him surfing a 4m (12ft) plunging breaker behind the wheel of an amphibious Dukw truck weighing around 5.5 tonnes (6 short tons).
How exactly does paddling help? If you’re paddling as you catch a wave, you’ve already given your body a certain amount of kinetic energy and momentum, so any oncoming wave has to provide you with less of the total energy you need to get moving: paddling, put very simply, gives you a head-start in terms of kinetic energy and momentum. It doesn’t help you with potential energy: unless you’re lying prone on a bodyboard, you’ve still got to get upright!
What about medicine? Does the physics tells us anything useful about that? From the viewpoint of materials science, bone is a material like any other: it has its limits, and it will fracture when you subject it to a certain amount of force (powered by a certain amount of energy). I’ve seen various estimates of the kind of force required to break bones—and it obviously varies according to which bones you’re talking about, the age of the person involved, the nature of the impact, and how inconvenient a trip to hospital would be right at that moment. But let’s do some more school-level, back-of-the-envelope scribbling and see what happens. Isaac Newton’s famous second law of motion (the one that says soccer balls accelerate when you kick them) tells us the force a breaking wave delivers is equal to the rate at which its momentum changes (so, mathematically, F=ma or F=mv/t). If we return to the same breaking wave we looked at a moment ago, we know m (600kg) and v (11m/s) so let’s guess that the wave breaks in 1 second (for super-easy sums). That tells us the force involved is about 600 x 11 /1 ~7000 newtons. Enough for a fracture? Certainly. A quick bit of online searching suggests a ballpark estimate for the force needed to break a bone might be several thousand newtons.[12]
But different waves deliver very different force even if they contain the same amount of energy. Why? Think of sudden-impact car crashes, which hurt you much more than slower ones: cars are designed to crumple to slow down the impact, so your body feels less force and the chance of life-threatening injury is dramatically reduced. In exactly the same way, waves that break faster produce more force, which is why a plunging wave that closes out in a shore-dump is more dangerous than a wave that peels gradually across its width. Simple physics tells us why: if two waves contain exactly the same amount of energy but one breaks five times faster than the other, it can (theoretically) deliver five times the force (because F=mv/t and if t is five times smaller, f is five times greater).
In the last article, we looked at the heat energy in the oceans and why you need to wear a wetsuit. This time we’ve looked at the energy in waves. In the next article, I’ll be looking at how waves travel over the ocean and form themselves into perfect surf.
Surf Science by Tony Butt and Paul Russell. Honolulu, Hawaii: University of Hawaii Press, 2002. The most accessible introduction to surf science you’ll find. Very clearly illustrated and with a minimum of maths, this is the perfect starting place for surfers who love a bit of science.
Waves and Beaches: The Dynamics of the Ocean Surface (Revised edition) by Willard Bascom. Anchor, 1979. A classic introduction to the physics of moving water, this book covers the basics of how waves form and move, though topics like ocean energy and coastal defence also get a mention. Again, there’s very little maths here to bog you down.
Wind Waves: Their Generation and Propagation on the Ocean Surface by Blair Kinsman. Dover, 1984. This one’s for experts only. It’s somewhat dated, but well worth browsing, if only to convince yourself just how complicated wave science really is. You can browse quite a lot of it for free via Google Books (follow the link and click on the book cover).
Notes
[1]: Unfortunately, that doesn’t mean every square metre gets 1000 watts all the time: obviously, you have to be facing the sun! For a good discussion, see “Chapter 6: Solar” in Sustainable Energy Without the Hot Air by David MacKay. Cambridge: UIT Press, 2009, p.38.
[2] Kelvin-Helmholtz clouds offer the most obvious visual comparison between sky and ocean. Check out this great photograph at The Cloud Appreciation Society.
[3] Just as waves form at the interface between the atmosphere and the ocean, so they can occur at the boundaries between different layers of water deep beneath the surface. Check out this article and photo from the NASA Earth Observatory, which shows underwater waves spotted from the International Space Station!
[4] For a history of the world’s biggest waves, see The Sea: Tsunamis by Eddie Bernard and Allan Robinson (eds). Cambridge, MA: Harvard University Press, 2009.
[5] My accounts of the rockfall in Alaska and the giant Cretaceous tsunami were researched using “Chapter 8: Waves and Water Dynamics” in Essentials of Oceanography (Sixth Edition) by Harold Thurman and Alan Trujillo. New Jersey: Prentice Hall, 1999, p.244-245.
[6] Huge California waves attract US surfers. BBC News, 29 August 2014.
[7] “Chapter 8: War and Peace” in New Scientist: Farmer Buckley’s Exploding Trousers: And Other Odd Events on the Way to Scientific Discovery by Stephanie Pain. London: Profile, 2013.
[8] You can find a fairly basic—though typically unclear—introduction in the Wikipedia article on Wave power. That gives an estimate of 36kW per meter for a deep water wave well away from the shore. To see how complex this subject really gets, check out one of the classic books, Blair Kinsman’s Wind Waves: Their Generation and Propagation on the Ocean Surface, especially “Chapter 11 Energy considerations” (p.516).
[9] Waves and Beaches: The Dynamics of the Ocean Surface (Revised edition) by Willard Bascom. Anchor, 1980, p.241.
[10] Thurman and Trujillo (see note 5), figure 8–25 on p.270 gives a diagram of likely wave energy potential for different coasts around the world. Values range from about 10 kilowatts per metre (in sheltered areas) to over 60 kilowatts per metre for super windy parts of the southern continents (the south coast of Australia, South America, and South Africa) where wave heights routinely exceed 3m (10ft). That gives a broad range of 10–100 megawatts per kilometre.
[11] Renewable Energy: Sustainable Energy Concepts for the Energy Change by Roland Wengenmayr and Thomas Bührke. Weinheim: John Wiley, 2013, p.103. For a quick review of how LIMPET turns wave power into electricity, see Bath University’s Wave Power: LIMPET page.
[12] See for example Brute Force: Humans Can Sure Take a Punch by Charles Q. Choi, Live Science, 3 February 2010, which estimates 4000 newtons for the force needed to crack a rib.
“Rip Currents … What Every Water User Needs to Know” by Tim Jones
Rips are, to most of us, a fantastic aid to our surfing when understood. They help us pass out through waves to the takeoff area and often they define the “peak” and create a better breaking wave.
So what are rips? A definition from the US Coast Guard …
RIP CURRENTS ARE POWERFUL CHANNELS OF WATER FLOWING QUICKLY AWAY FROM SHORE … WHICH OCCUR MOST OFTEN AT LOW SPOTS OR BREAKS IN THE SANDBAR AND IN THE VICINITY OF ROCKS AND STRUCTURES SUCH AS GROINS, JETTIES AND PIERS
However, they can also be a source of danger especially to those who are unaware of their existence. So here are a few interesting facts and basic statistics.
Annually, in the US, there are on average 100+ deaths from rips. In the UK, two in every three (2/3) water rescues are because of rips. Rips in the UK account for more deaths than bicycle accidents!
In Australia (2004‚ 2012), deaths per year attributable to Rips = 21; Cyclones = 7.5; Bush fires = 5.9; Floods = 4.3; and Sharks = 1. So when many beach goers in some parts of the world fear a shark attack, they would be far better served to understand and spot rips and respect the dangers they represent.
So how do we change the stats?
We, as surfers, can pass on this basic knowledge to others, surfers, or not. Remembering the US Coast Guard definition above, and observing the simple diagram of how rips work below, we can understand a few key principles.
There are a few different types of rip and these are:
Permanent or Topographic
Fixed
Flash
Travelling or Side Rip. Not long shore drift.
The Permanent or Topographic Rip
Let’s look at how each is defined. Firstly, the Permanent or Topographic rip uses physical features at the beach such as: rocks, piers, groins, sea walls and the water (rip), running out along these features. To help you find it, just look at how next to the feature there seems to be an area of calm water with little or no waves. In this picture below you can see the rip passing along the beach towards the cliffs. This is our Travelling or Side Rip. Then you can clearly see where it passes along the rocks and heads out to sea causing a clear path in the water. Look for the dark blue line with the white water each side. You can clearly see its path along the rocks and out to sea. Check how, as it moves away from the rocks, it loses it power and dissipates.
In this picture from Australia, the lifeguards have placed a coloured dye in the water to define the Permanent or Topographic rip.
The Fixed Rip
It’s quite a misleading name, “Fixed”, as these are rips that stay in one general area of a beach, but can move even up to 100m from one side to another. This is due to the change in density of the sand by wave action and the general topography of the beach. The picture on the right shows the gap in the surf line and the travelling rip which is coming from the left hand side of the beach (looking out to sea) and feeding into the rip.
Of course, we may get more than one type, or even all types, of rips occurring on a beach. Here is a particularly illustrative example. At the top of the picture we see a Permanent or Topographic rip running out by the rocks and road (note the absence of surf) and then below is our fixed rip causing a break in the surf line yet again.
Flash Rips
These often occur when a sand bar on a beach breaks down by wave and tidal action or as the tide moves past an outcrop of rocks. The diagram below illustrates typically how such a rip can arise. As the name suggests, they occur suddenly and can often be a great danger to swimmers who often do not know what to do if caught unawares in them.
How wide are rip currents, how fast can they flow, and where do they go?
On average, rips are typically about 9.5m or 31ft wide, but this is a real average as they can be less or more, and particularly the flash rips ‘begin’ by being very narrow. However, it’s a good rule-of-thumb to remember that they are normally about “as wide as a bus is long”!
They move on average at approximately 6.6kph or 4.1mph. That’s some speed, about the same pace as Olympic 400m Gold Medallist, Sun Yang’s average pace. Little chance then of out swimming or out paddling the rip.
Rips flow out to sea to a distance really depending on the volume of water that’s flowing into the beach. They go to an area we call the Head. So on a small day of surf the rip may stop and form the Head only a few hundred metres out to sea. On a big day of surf you may find it flowing kilometres out to sea. Below is a classic example of a beach break rip leading to a head, but of course heads can be found on reef set ups as well. The famous Sunset Beach in Hawaii is a great example. Lost boards there are often never found again!
Caught in the rip?
Now let’s hope that this advice is not needed if you’re a regular surfer. But do pass it on to others new to the sport or those who are just happy water users anyway. Firstly, prevention, don’t let the situation happen in the first place. Get advice about the beach and the surf you’re using and be able to spot the rips before entry, but more of that later. If someone is stuck in a rip, the first rule is don’t panic, and don’t whatever you do try to paddle or swim against it. Remember how fast it is going and just go sideways and towards the breaking waves that can help you. The picture below is simple and a good example of the action to take.
NOTE: Emerging evidence suggests that simply threading water and waiting for the rip to dissipate may be a prudent approach when caught in a rip. Currently, the approach described previously and illustrated above, i.e. swimming parallel to the shoreline/at right angles to the direction of the rip, is advocated by most surf lifesaving institutions and lifeguard professionals. Further research is required to definitively determine the safest strategy. For further information, check out this insightful article New Scientist article on research conducted at the Naval Postgraduate School (NPS) in Monterey, California, USA.
Know the Emergency Signal
It’s worth keeping in mind that people often want help even if they know what to do in a rip or when they see others caught in a rip. It’s a simple one arm in the air and waved from side-to-side to attract attention. This is like a 112 or 999 call of the sea and should be known by all and passed onto others. Just knowing this could save someone’s life and perhaps your own.
Many beaches now carry signs to remind us as shown here. Of course, just getting advice from locals and particularly lifeguards at beaches is number one. Remember, prevention is always better than cure.
So, we need to be aware of the dangers of rips, but also we may be experienced enough to want to use them to access the best surf.
So how do we spot them?
Here are some simple indicators:
1. A gap in the waves or where waves break then “back-off” (die out) and then reform again. The water moving out either stops the waves, creates a channel, or just stops the wave from breaking.
2. The surface of the water has ripples on it even if there is no wind at all. If there is wind, it seems more wind affected. Again, this is the outward movement of water creating the surface affect.
3. The rip will carry sand, seaweed, derbies and pollution. This is often a very clear indicator of a rip.
Line-ups
In order to help us use rips correctly, or to keep others away from them, we need to develop the skill of using line-ups. These are markers on the beach that help keep position in the best surf zone, and thus getting the best waves.
Also, choosing line-ups keeps others safe. Lifeguards do this all the time, setting safe swimming areas marked by flags. If you check the photo below you could choose many line ups from houses, trees, etc. But never choose objects that may move like an umbrella on the beach or a parked car for example.
So rips, although dangerous to those who are unaware of them, are often our best friends in surfing. Take time to observe the ocean before entering and never be afraid to ask questions. Be aware that some rips will take us out to surf we just can’t and don’t want to handle, and other rips will take us out to the best waves of our lives. The main reason for this article is to get you to transmit this basic knowledge to others so we can all enjoy the ocean in a much safer way. Thanks. Stay safe in the water.
The author carving a roundhouse cutback!
Tim Jones is an EASD Scout, International Surfing Association (ISA)/Surfing Great Britain (Surfing GB) certified Surf Instructor and Coach. He is¬†Director of Surf School Lanzarote. Tim has a long and active history with Surfing GB, beginning the first special needs initiative for surfing in the UK, and continues to contribute to the development of coaching skills within the organisation. The current women’s Welsh Junior and Senior Champion, Emily Williams is coached by Tim, as have past champions in Europe such as Mark Vaughen and Nathan Phillips.
The European Association of Surfing Doctors wishes you and yours a very Merry Christmas and Happy New Year!
Gastrointestinal symptoms in surfer populations (during the Christmas season!)
Don’t swim immediately after eating. Picture Credit: Irish Water Safety.
OK, it’s that time of year again and Christmas is creeping up on us fast. Before you know it, you’ll be loosening the top button – Homer Simpson style – after a festive turkey feast!
For those of us graced with waves this Christmas, we may be tempted into the water despite the seasonal chill. It seems quite intuitive; indeed, prudent public-information notices, such as that shown here by Irish Water Safety, remind us not to enter the water immediately after eating. But when the surf is pumping … well, you know, it can be difficult to sit on the beach.
I recently came out of the water to be greeted by the not-so-pleasant retching of an overzealous grommet. When I approached him, asking if he was all right. He replied:
“I was starving, wolfed down my lunch before getting in … wicked heartburn!”
Long story cut short, he lived. But the episode brought to mind a distant Friday Facebook Fact (FFF) about a study looking at Gastrointestinal (GI) symptoms in surfer populations.
Paddling (Prone) at Conference 2014
Back in 2009, that’s exactly what Norisue et al. examined. Their study compared the prevalence (i.e. how common an occurrence) of GastroEsophageal Reflux Disease (GERD) in surfers versus non-surfers who participate in other sports.
How did they do that?
Their hypothesis was based the fact that paddling in the prone position, i.e. lying on your stomach, on hard surfboard surfaces leads to raised pressure within the abdomen and hence GERD. The authors used a modified version of a validated questionnaire survey called the Gastrointestinal Symptom Rating Scale and obtained their data from 185 surfers and 178 non-surfer athletes on the Hawaiian Island of Oahu. They also collected information on risk factors (things that increase your likelihood of developing a given condition) for GERD, type of surfboard ridden, frequency of surfing, and duration of surfing experience.
What did they find out?
The prevalence of GERD was significantly higher in shortboard riders than in non-surfers with an odds ratio of 4.6 (28% versus 7%, P<0.001) after adjustment for demographic variables using the multivariate regression model. GERD was more prevalent in shortboarders than longboarders (28% and 12%, respectively). Furthermore, the more frequently you surfed, and the longer your surfing history, GERD increased significantly (P<0.001).
The bottom line …
Norisue and his colleagues concluded that surfing, especially shortboard riding, is strongly associated with gastroesophageal reflux disease (GERD).
Reference:
Norisue Y, Onopa J, Kaneshiro M, Tokuda Y. Surfing as a Risk Factor for Gastroesophageal Reflux Disease. Clin J Sport Med 2009;19:388–393.
Papa-he-nalu, planches de surf, surfbretter, サーフボード, tablas de surf; call them what you will, it really doesn’t matter: WE LOVE SURFBOARDS. What’s more, wave riding is our passion. So, no matter whether it’s on a mat, your belly, or with a hand plane, keep on doing it!
That’s why we have invited the very best in Irish surfboard shaping and design to the Shapers Forum at the Surfer’s Academy on Saturday 13th September 2014 in The Glasshouse.
Fergal Smith at the Moy Hill Community Garden (2014).
The first time I met Fergal I was pleasantly surprised by how affable, unassuming, and down-to-earth he was. We talked about common interests; no, not surfing especially (although it may have been discussed), but trees. Fergal and his brother, Kevin, had only recently begun posting their Growing Series online. It was through this medium that I became aware of the full extent of his horticultural endeavours and, perhaps lesser acknowledged (in media circles at least), passion. Fergal and a motley-crew of locals, nomad surfers, and on any given day, warmly-welcomed volunteers, are staging a silent revolution at the Moy Hill Community Garden.
That same initial meeting, at the Shore Shots Irish Surf Film Festival, occurred shortly after watching the excellent documentary Unchartered Waters by Craig Griffin about Wayne Lynch. In the fullness of time, I can’t help but smile when I reflect on the uncanny coincidence, or rather resonance of both surfers’ journeys; the parallel, or blurred, lines if you will.
Wayne Lynch: The surfer who took wave riding out of the horizontal and into the vertical (2013).
Both goofy-footers, both prodigiously talented – Fergal will deny this, attributing his prowess to hard-graft – surfers at an early age, both seemingly ‘dropped off’ the radar at the peak of their success.
Lynch, once described by Reno Abellira as “…the Future of Surfing Incarnate”, shied away from publicity saying that he wanted to be “just a surfer, not a star”. Later it emerged he spent close on three turbulent years on the run from conscription and Vietnam! For many, Jack McCoy’s 1978 film, A Day in the Life of Wayne Lynch, defined what we’ve come to know as the ‘Soul Surfer’.
SURFER Magazine (2012). Telling the world what Irish surfers already knew.
In many ways, Smith’s trajectory is not dissimilar. Thankfully, no military-service or conflicts to mention; sponsor courtship, fanfare wildcard invitations to spots like Cloudbreak and Teahupoo: All heady stuff for a young surfer! Gone (partially) are the cover pages (see SURFER Magazine cover) and fewer sponsors remain. Nonetheless, Smith carries on regardless. Paddling heavy waves is what matters. For him, this is where the heart runs deepest in surfing.
Most of the breaks that he, and a core group of surfers based in West Clare, ride are relatively virgin waves in the Irish surfing historical timeline. The rulebook is quite literally being rewritten with each substantial swell. The unprecedented swells of last Winter are case(s)-in-point, making for limit-testing feats and pioneering wave riding on these shores.
Feel from sponsorship agendas and the distraction of ‘Surfing Industry’ concerns, Fergal can now dedicate himself wholeheartedly to the pursuit of waves of consequence on his own terms. The reality of the opportunity afforded him by past sponsorship is not lost on Smith. Yet, central to his decision to change tack was Health and Well-being. Stepping aside from the corporate surfing world has enabled focusing on his other great interest in life: Growing Your Own. Easily understood in the context of his upbringing, Fergal grew up on an organic vegetable farm outside of Westport, Co. Mayo. Now based in Clare, he is the talisman of a community-supported renaissance in growing wholesome nutritious food. ¡Viva la Revolución!
Fergal Smith will speak about his personal journey at the Surfer’s Academy – Chasing Dreams, Charging Waves, & Coming Home to Ground.
Why not check out the Surfer’s Academy Trailer Series – Four Boards and A Piano by Kevin Smith, featuring Fergal’s masterly wave riding, will be shown during the Surfer’s Academy at The Glasshouse on Saturday 13th September 2014. Tickets cost €25/person.
“I paddled fast to my left, angling toward the next wave, stroked and stood and felt the board accelerate and pumped once and into my bottom turn, and then the world vanished. There was no self, no other. For an instant, I didn’t know where I ended and the wave began. This was an instant beyond the redemption I had hoped to find.”
The Eternal Present: In-The-Green-Room
Excerpt from West of Jesus: Surfing, Science, and the Origins of Belief by Steven Kotler (1).
Kotler goes on to describe surfing as “a game of such [transitory] instants”. Transitory in that those moments are both “staggeringly impactful and simultaneously vanishing”. The Glide, In-the-Green-Room; familiar terms which attempt to capture our experience, but “truthfully refers to the feeling of being utterly, finally, fleetingly, awake”.
The Concept of Flow
Getzels and Csikszentmihalyi (2) looked at the creative process artist during the 1960s. They found that when work on a piece was going well the artist persisted without distraction, ignoring tiredness, hunger, and discomfort. Further research by Csikszentmihalyi (3) went on to examine the subjective phenomenology of intrinsically-rewarding activities in groups such as rock climbers, dancers, and chess players. They found remarkable concordance across work and play settings. The general conditions of flow included:
Being engaged in an activity that ‘stretches’ one’s existing skill-set at an appropriate level commensurate with capability
Clear proximal goals and instantaneous feedback regarding progress made
Greenough: Surely the foremost proponent of Flow in every meaning of the word
Nakamura and Csikszentmihalyi reported that being “in flow”, and under such conditions, our experience “seamlessly unfolds from moment to moment” (4). They described the subjective/experiential state one enters as having the characteristics listed below. It’s worth noting the undeniable corollary to Mindfulness.
Intense focus and concentration in the PRESENT moment
The moment, awareness, and the action (i.e. doing) become one, with a loss of self-reflection (i.e. ‘external observer-like awareness’ of oneself as a social actor)
A sense that one can respond to, perhaps even anticipate, imminent events
Temporal distortion (e.g. ‘time slows down in the barrel’, or perhaps speeds up)
The activity and experience of same is intrinsically rewarding to the extent, perhaps, that the end goal simply becomes an excuse for the process – Sounds familiar?
The latter recalls the Pezman–Leary (5) interview referenced in our previous post Drop-in Turn-on Tune-out: Commitment, Death, and Anxiety. Leary, in response to the author’s statement that surfers are discovering that “surfing is pretty much a head game in a fluid medium”, offered his understanding of the surfing experience:
“…a merging of your own body neuromusculature, or brain body, with the power/energy/rhythm of nature. That’s what’s so jewel-like precise about mind/body/sea energy interfacing together. One thing I like about surfing is that it is all out. You can’t be half-hearted, or you can’t be thinking about something else. You’ve got to give up all the land, social, cultural, moral, political whatevers … you’ve got to be totally there.”
Far out dude; perhaps, yet there’s no denying the underlying grain of truth. Pezman went further, making a keen observation, when he said:
“It’s also interesting to note that surfing is non-productive…non-depletive, almost a nonentity. Your wake disappears from the ride, the wave dissipates on the beach. The surfer leaves at the end of the day, and there’s no trace. And yet you get hooked on doing this thing.”
Well, you can say that again!
Boris Bornemann
Cool, I’d like to know more about Flow States and Mindfulness
Boris Bornemann, Dipl.-Psych./Master Sc., PhD Student at the Max Planck Institute for Human Cognitive and Brain Sciences, Department of Social Neuroscience, Leipzig, Germany, will explore Flow and Flow States in Surfing at the Surfer’s Academy on Saturday 13th September 2014.
Dr. Tony Bates, Clinical Psychologist and Founder of Headstrong will discuss Resilience, Living Mindfully, and Mental Health at the Surfer’s Academy.
All attendees must REGISTER Online. Under sixteen (16) year-olds go free. Ticket Cost: €25.00/person.
References:
1. Kotler S. West of Jesus: Surfing, Science, and the Origins of Belief. Bloomsbury, New York, USA. 2007
2. Getzels JW, Csikszentmihalyi M. The Creative Vision: A Longitudinal Study of Problem Finding in Art. John Wiley & Sons, New York, USA. 1976
3. Csikszentmihalyi M. Beyond Boredom and Anxiety. Jossey-Bass, San Francisco, USA. 2000
4. Nakamura J, Csikszentmihalyi M. The Concept of Flow. Snyder CR & Lopez SJ, Handbook of Positive Psychology, pp89-105. Oxford University Press, New York, USA. 2001
5. Pezman S. Dr. Timothy Leary, The Evolutionary Surfer. SURFER Magazine. Jan 1978, Volume 20 Number 8
Note: Featured Image on front page that accompanies this post is ‘Tales from the Tube’ (1971) by Rick Griffin.
“Surfing gives you very elemental illustrations of broader truths by serving as a microcosm that we can grasp”
“Turn On Tune In Drop Out”: Timothy Leary, captured by Art Brewer, in existential chat mode, 1978.
– Steve Pezman, surfing sage, The Surfer’s Journal Publisher, and then SURFER Magazine Editor in conversation with countercultural icon, Timothy Leary, in 1978 (1,2).
Just one articulation of why surfing means so much to us. There are many lessons in surfing that we take ashore for life after the ride.
How to balance the fearsome view of a story-high barreling wave and the urge to ride it?
Bated-Breath: Brock Little during the Eddie Aikau, Waimea Bay, 1990. Can we learn from this? Photo Credit: Erik Aeder
Life is inconsistently peppered with critical moments, crossroads, dilemmas that test our confidence, courage, and resolve: illness, trauma, loss. Often, we find ways to avoid these moments. Dropping-in serves as a model for confronting anxiety. A thorough understanding of the psychology of dropping-in can lead to a more engaged and contented life.
Dr. Greg Dillon is a psychiatrist and dynamic psychotherapist with a special interest in the uses of experiential therapy, particularly surfing, as a visceral and metamorphic point of access to intra-psychic processes. He has written and lectured on his theories for Psychology Today, and is working on a book and seminar series called Surf-Head, exploring the lessons of surf and sea towards a better self understanding (3).
Dr. Greg Dillon (USA)
How can I learn more about this topic?
Dr. Greg Dillon will lead the workshop The Surfers Head at Conference 2014 and explore the Psychology of Dropping-in during the Country Soul section of the Surfer’s Academy on Saturday 13th September 2014.
The Surfer’s Academy marks the beginning of the EASD’s Outreach Program – translating our vision of “Keeping the Surfer Healthy and Safe”.
It is a full-day Health and Well-being Symposium for Surfers about the issues that affect them in and out of the water.
John “Doc” Ball
Surfing and doctors … what’s with that?
We’ve always been there in the line-up. So we figure it’s time to drop-in and give something back. The Surfer’s Academy, the first event of its kind anywhere, will see you surfing safe and staying healthy into your twilight years. Surfing and Medicine have always been close; from John “Doc” Ball – pioneering surf photographer and Coast Guard Dentist – to the free-spirited, Dr. Dorian Paskowitz, still stoked at 93! And let’s not forget big wave forerunner Dr. Mark Renneker who has been silently charging the Californian coast and beyond for years.
OK, Cool … So who will be there?
Join leading Experts in: Eye, Ear, Mind, Nutrition, Shoulder/Major-Joints, Lifeguarding, Big Wave Rescue – you name it, we’ve got them lined-up – let them take you through what you need to know, how to stay healthy, and improve your surfing experience!
EASD Ambassador, Peter Conroy
Irish Big Wave Legend, Peter Conroy will share his experience of Big Wave Surfing and Rescue. Miguel Moreira, Professor in Human Kinetics/Surf Science and Technical Adviser to the Portuguese Surfing Association will speak on Training and Performance in Surfing. Psychiatrist, Greg Dillon, from New York City, will take you through the psychology of dropping-in and how this relates to the challenges in life and how we overcome them.
Arguably Ireland’s most talented surfer in a generation, Fergal Smith will retrace his personal journey from pioneering Irish slabs, to ‘wild card’ billings at spots like Teahupoo and Cloudbreaks, to finding his balance closer to the natural world back home in Co.Clare. Tony Bates, Clinical Psychologist and Founder of Headstrong will discuss resilience, living mindfully, mental health and well-being. Australian Strandhill-local surfing Physiotherapist, Derek Parle will talk about shoulder injury, rehabilitation, and the principles of prevention. Too much to mention … so check out the programme for further details.
What else will be happening?
We’re stoked to team up with a range of pro-active national and local organisations to bring you an outstanding event!
Clean Coasts Ireland will speak about community-based Coastal Guardianship; involvement in the ‘Beat the Microbead’ initiative, and bathing water quality. There will also be a Surfer’s Academy Beach Clean organised by Clean Coasts Ireland and supported by the European Association of Surfing Doctors and Surfrider Foundation Europe the next day (Sunday, 14th September 2014), followed by a visit to Strandhill People’s Market to enjoy the best in local artisan food and crafts. Come along … get involved … protect what you love!
As well as spot-prizes, world-class photography (including prints by hotly-tipped Irish surf photographer, Christian Mcleod, recently listed by ‘Inertia’ as one of ten ‘Up-&-Coming Photographers’ to watch in surfing!) and David Olsthoorn, a retrospective of the Surf Art of Barry Britton: 40 Years of Irish Surfing History, a “Shapers Forum” showcasing the best of Irish Surfboard Shaping and Design by the likes of DH Surfboards, AOR Surfboards and others, the list is endless …
Of course, apart from an amazing symposium, the West Coast breaks need no introduction. Just another great reason to organise your surf trip!
And the best thing is … those under 16 years of age go free (See Note 1).
ALL attendees MUST REGISTER ONLINE to attend this event.
Ticket price for the Surfer’s Academy is 25 Euro.
#surfersacademy #easdireland2014
Note 1: For insurance reasons under 16 year-old attendees must be accompanied by an adult.
*At the Surfer’s Academy on the 13th September all medical conference attendees are welcome to join, but as our aim for this day is to translate our vision of “Keeping the Surfer Healthy and Safe” into a reality, surfers (i.e. non-medically trained, non-conference attendees) that register will be given priority seating in the conference room. We will arrange TV screens with live broadcast (in the same building) and seating outside of the conference room should the capacity of the venue be exceeded.
Suppose we have a 1m width of a wave that closes out completely, with the water coming to an impossible, screeching halt (so effectively it loses all its kinetic and potential energy when it breaks). According to Willard Bascom (one of the founding fathers of surf science), the speed of a decent surfing wave is about 40 km/h (25mph or 11 m/s).[9] For easy sums, let’s assume the wavelength (the distance between one wave peak and the next one) is 2m and the amplitude (the height of the wave) is also 2m, so the volume of water above the mean sea level that we’re interested in (the dark grey bit in the figure I’ve drawn here) is roughly 1 x 1 x 0.6 = 0.6m3 = 600 litres, which weighs about 600kg. Simplifying very greatly indeed (I know, I know… but bear with me), that gives us potential energy of mgh = 600 x 10 x 1 = 6000 joules and kinetic energy of ½mv2 = 300 x 11 x 11 = 37,000 joules, making a grand total of about 43,000 joules—or call it 50 kilojoules to keep things simple. This is a rough estimate of how much useful (non-heat) energy there is per metre of a simple breaking wave—and the actual value is likely to be less than this because of all the simplifications I made (a real wave isn’t this steep; it doesn’t stop completely when it breaks; it has an ever-changing, irregular volume; its total mass is not all concentrated at exactly the same height; and so on—this is back-of-envelope, guerilla physics!). Remember that this is the energy in a single meter width of water—so a stupendous wave shattering into sand across 1km (0.6 miles) of a bay could theoretically deliver 1000 times more energy than that: a wave like that breaking each second could theoretically make 50 megawatts of power (equal to about 25 very large wind turbines).
