SURF - IT'S ALL ABOUT POWER !

Been surfing for long and you'll find there are days when you go to a beach and the waves just seem to have more power....... ever wondered why? Well of course there are a number of contributing factors, but we'll focus on a couple of the key components. They are - the shape of the wave before it gets to the beach, and the topography of the seabed. Both are critical to making the wave break nicely.... or nastily....

So first of all - we need to understand a bit about breaking waves. Oceanographers call breaking waves by different terms depending on how they break. When the white water just creeps down from the top of the wave to the bottom - these are called 'spilling' breakers. They can be small or large, and you can surf them nicely - but they just won't feel very powerful. These tend to occur on beaches which are very wide and very flat. The next class of wave is the 'plunging' breaker. This term is used when the white water goes straight from the top of the wave to the bottom of the wave. This class of wave includes the classic tubing waves that you may - or may not - be looking for!. Plunging breakers are generally formed on steeper beaches, or by steeply shelving reefs under the sea. Basically what's happening is that as the wave gets into shallower water, it is forced to slow down. The wave breaks when it reaches some critically shallow depth - with bigger waves breaking in deeper water. The water particles in the top of the wave find out about this after the ones at the bottom, so they essentially over-turn the wave. So if you present a fast moving wave with a steeper reef, it'll throw out a bigger lip..... Anyhow - if you want power in your waves, plunging breakers are the ones to seek out....

A particularly important factor comes in to play before the wave even gets to the beach. It is the wavelength of the wave - that is - the distance between two successive wave crests. Now you're thinking -how do I find out what that is? Well - help is at hand ! - On the swell-charts on the web (see below), you may have noticed the 'wave period' next to the 'wave height' charts.

Try these : http://152.80.49.210/PUBLIC/ or http://152.80.49.210/PUBLIC/WAM/

The period is simply the time interval between successive wave crests. Far offshore, the wave period is related directly to the wavelength - larger wavelength waves have greater wave periods. Why is this important ? Well - waves with longer periods tend to plunge rather than spill - and so feel like they have more power when you surf them! So - choosing a time when the waves have a larger wave period is particularly important when looking for good surf ! (Hot tip - I generally find wave periods greater than about 9 seconds on the wave charts indicate a good swell, provided the height is sufficient. Typically you'll get some excellent surf if the height is up at around 5 feet, when combined with a 9 second period...)

The next key component for the surf to be any good for riding is the angle that the waves approach the break. Why is this important ? Well we've all heard of 'close outs' and 'making sections' - well the key thing that's being talked about here is how fast the white water appears to travel along the wave. If the whole wave crest is parallel to the beach, it'll all break at once, and there wont be a shoulder to ride. However - if a wave approaches at a slight angle to the beach, then one end breaks first, because it hits the beach first. You, the surfer, can then travel along the wave, using it's power to propel yourself from one end of the beach to the other...... or that's the theory....

Of course - this works well on reef breaks on annoyingly picturesque reefs in blue oceans.... The reef sits at an angle to the swell, and perfect shoulders are formed for sun bronzed idols to effortlessly glide along...... Back here in good old Blighty we generally have to cope with sandy beaches and beach breaks. But the theory is the same. You'll generally find that there'll be a spot on the beach where the waves are peaking up nicely - and you can bet there'll be a sand bar underneath this point. Just along the beach, you'll normally also find a channel and a rip. The waves break first on the seaward most point of the bar, and the shoulder travels alongshore, towards the channel or rip, until the whole wave is broken. So creating a feature just perfect for you to ride on! Sand bars that tend to lie more parallel to the coast force their waves to break along their length in a shorter time - so produce a shoulder which travels along the wave more quickly. Sandbars that have flanks that slope at an angle to the beach produce slower shoulders. You choose your spot depending on what craft you have, and how fast it goes! Unlike the reefs, sandbars have a habit of moving - thereby complicating the issue, but that's another story.

So there you have it - enough wave talk to keep you entertained next time you are having a good old rinse around in the surf - whether it's powerful or not.

Any questions, or anything specific you'd like to read about? Email - will@goatboater.com

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