| Rolling in Wavetrains by Chris Joosse | ||
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Big waves can be big, big fun, but they present special challenges as well. There are a lot of great things to do with waves, such as rocket moves, wave-wheels, barrel-rolls, plain old surfing, you name it, we do it and what's more, it's some of the best fun around- but we all get flipped in big wave trains, and we've all blown rolls there- so for some of us, big waves represent a voodoo of a sort we can't quite approach with carefree abandon. In this article we'll discuss just what's going on in a big wavetrain, some of the things that can help or hinder a roll in this environment, and some strategies by which you can make your rolling efforts more efficient and more reliable in big waves. In this article we will discuss the specific challenges to rolling that are presented by wavetrains. We will not review how to roll. If you're interested in that, follow the link, read up on it, and work with a knowledgeable paddler or instructor who can provide you with feedback. Understanding Waves To begin with, it helps to understand what waves are doing- in a river, water is constantly accelerating forward into the trough, and decelerating as it approaches the next peak- that is, the mass of water flowing downstream is stretching, piling up, then stretching again, in addition to the more noticeable up-and-down movements we all seem to notice right away. This bit of information gives us the beginning of a perspective from which to consider the challenges we face when performing regular tasks, such as rolling or bracing, in this environment. First, the good news: In as dynamic and largely predictable an environment as this, there will be forces you can exploit in order to make your roll physically much easier than it is on flat water. The bad news, of course, is that in such a dynamic environment, you will face constraints in your timing- the same force that'll help you at one point in the wave is apt to reverse itself and resist you the next. First, a brief overview on what causes a wave: We've all seen a diagram of water flowing over the top of a boulder or other obstruction, but what happens then? The long and short of it is this- when water accelerates due to gravity, it changes shape- and when it slows down due to incompressibility and drag, it also changes shape. A wave, then... is an expression of pressure systems created by water (which is incompressible) speeding up and slowing down against itself and the riverbed that constrains it. So waves are what happen when a whole mass of water slows down and piles up, then speeds up and drops away. There will be 3 factors that will shape your strategy for rolling in wavetrains- Acceleration/deceleration forces, inertial 'gravity' fluctuations, and the grain of the wave. Your minimum-gravity moment occurs at the peak of each wave, your greatest paddle-purchase occurs in the trough of each wave. You'll experience more gravity as you go up the face of any given wave, and less of it as you go down the back face. The rest is timing and relies on the same roll you already know, with one extra step- we'll call it 'active setup'. Acceleration and deceleration- As you move down the face of a wave, you'll be in a field of water that is accelerating into the trough. Similarly, as you move up the face of the next wave, you'll be in a field of water that is slowing down. This is important to grasp because in a field where inertial acceleration and deceleration is occurring, your balance is going to be affected, and if you're trying to roll you'll want to understand what's going on with it. If you're standing in a bus as it accelerates, you must lean forwards or you'll fall over. Similarly, if the bus is decelerating, you need to lean back in order to remain balanced. In other words, 'up' isn't necessarily straight up when it comes to balancing. This is important because of the way we think about rolling- often we're tempted to think that it would make sense to roll in such a way that we come up on the 'high' side of a given wave's slope, but this actually isn't the case. Remember, water always seeks it's own level, right? Well, in the context of the acceleration and deceleration fields that shape the waves, nearly any surface of a non-breaking wave is more or less level, if you factor in the acceleration or deceleration that shaped it. * What this means is that if you're moving with the water, it doesn't matter if you roll on the side that faces 'down' into the trough or 'up' the side of the wave... and given some of the other dynamics of the wave, rolling on the 'up' side can be more difficult than the alternative.
Inertial 'gravity' fluctuations- As you go up and down, you experience a relative increase and decrease in the gravitational moment you express- at the bottom of the trough, as you go up the face of the next wave, you may feel 'heavier' than normal, while at the top of the wave, as you accelerate down the back face of it, you may experience a moment of 'lightness'. Of course, being heavy isn't all that bad unless your hip-snap (the part of your roll that does all of the mechanical lifting) is weak, largely because the mechanics of your roll rely on gravity to help you up. That is, once you've got the boat past halfway up, gravity is the force that helps keep the boat going in that direction. This is not to say that you can't use this 'low-gravity' moment to your advantage- if there's a moment in your roll (like, for example, getting from hip-snap to finish) that could use the help, it makes sense to time your roll to exploit it. Inside the wave- The wave is a structure shaped by pressure, gravity, and inertia, and it is from the inside of this structure that you will derive your traction- that is, it's what you'll be pushing/pulling against with your paddle, hands, etc. in order to accomplish your roll. Understanding the shape of a wave from the inside is obviously important, because without this understanding you won't be able to predict where and when your paddle will find purchase. Also important is the understanding that your paddle blade and you may span multiple phases of a wave- for example, it's not uncommon for you to be involved in the upstream half of a wave, moving upwards and decelerating, while your paddle (downstream of you) is involved in the downstream slab, which is moving downwards and accelerating away from you. In general, as the mass of flowing water is squeezed and stretched, it piles up and flows out of 'waves' in accord with the forces of inertia, gravity, and the pressure that is caused by both. Another important concept to understand is the idea of 'grain' as it applies to the wave in it's simplest form. By 'grain', we mean to express a tendency for a particular part of any given feature to push or pull you in a certain way. For example, an eddyline on river right tends to have a clockwise grain, whereas one on river left tends to rotate in the opposite direction, per the relationships of the two masses of water that are colliding. The same is true in a wave: as the water flowing downstream encounters pressure from the next wave, it piles up and as it does so, it introduces a certain grain as different parts of the water move at different rates and in different directions as a result. The result, as you may already be aware, is that during the course of a full cycle underwater in a wave, you will be pushed first one way, then the other as you, too, speed up and slow down. This grain will change in accord with the forces that created the wave. As the water flowing through the wave reaches the crest, the water near the surface that was moving rapidly upward will just as rapidly begin moving downward, while the water that was busy decelerating will begin to accelerate- essentially, then, as water flows through each transition phase of the wave, we see its grain effectively reverse itself as we flow through it. A non-breaking wave has two transition phases per cycle- the peak and the trough- meaning that in the course of a full wave cycle you'll be pushed first one way, then the other- and this is a useful pattern to be aware of, because it's the basis for getting that roll in big wavetrains up to 100% reliable. This 'push' will affect not just the way in which we can use the forces of the wave cycle to our advantage- it will also be a bit confusing at first, and it will affect the way in which we set up our rolls. As you might imagine, if you can't get your setup to work the way you like it, how ever will you get your roll to work? ...and if you can't figure out where you want your setup to be, how can you get it there? Active Setup- If you're used to waiting until you settle, then shoving your hands up and out of the water before attempting to roll, you'll want to get to know the Active Setup- that is, instead of letting yourself be pushed around until you're 'settled', you'll bring your paddle to the side of your boat as you would with any roll attempt, and begin a sweep away from the side of the boat with your power blade such that the blade climbs... and you can then reverse the angle of the active blade and sweep the other way, while still underwater, to scull yourself actively into a setup that's at or near the surface before engaging your hipsnap. Okay, so we've talked a lot about how waves work, and we've touched on actively setting up our rolls, but how do we actually USE all of this information? Here's the plan: If you're rolling towards the upstream side, roll just before the crest. You'll find that life will be easiest if you set up as close to the surface as you can manage, wait until you're on your way up the wave, and time your hipsnap to be completed before your paddle makes it to the crest of the wave. This way, your paddle gets to take advantage of all that water going up the front of the wave, while the rest of you begins falling and accelerating into the next trough. If you're rolling towards the downstream side, begin your roll just after the crest. You'll be taking advantage of a reduced feeling of gravity, and your paddle purchase will be solid, as your paddle will precede you into the solid, fast-moving water in the trough. If you're rolling side-to-side with respect to the waves, you can really roll any time you like, but you'll notice that the downdraft that occurs inside a wave on the downstream side provides very little succor. Use the time you spend going down the downstream side of a wave setting up, and time your roll such that when you need to use your paddle, it's involved in the updraft that occurs on the upstream side of a wave. breaking waves- the big exception: If you float upside down into a breaking wave, you can only roll in one direction- towards the downstream side. At this point, however, you're not rolling in waves... you're rolling in the hole, and I've written an entire article on that. Summary- With a reliable roll in the waves, the amount of fun to be had is limited only by your imagination and the laws of physics. Have fun! If you have questions or comments on this article, let me know about them. |