The mathematics of wind

From the Fall 2010 issue of Coast&Kayak Magazine. Read the entire magazine online.

By Alex Matthews

When kayakers talk about “conditions,” our primary concern is usually wind. Because more often than not, it is wind that will dictate when and where we can paddle and when we must stay ashore. And sometimes the most pertinent question is not “can we paddle in this wind?” but rather “how long can we paddle before exhaustion sets in?”

Wind has a profound effect on kayaks. Obviously, a tailwind is going to help push a kayak on its way, while a headwind is going to slow it down. Chart A to the right offers rough estimates of the effects that wind will have on the forward progress of a sea kayak.

Just as we’ve always suspected, a headwind slows us down more that a tailwind pushes us forward. Some things just aren’t fair! But bear in mind that a tailwind will generally also generate waves that will allow an experienced paddler to pick up surf rides, speeding him or her faster on their way than the push from the wind alone could generate.

Different paddlers counsel different strategies for dealing with a headwind. One old chestnut is to slow down and “conserve energy” for what will be a long arduous slog. Let’s do a little math and see what numbers we get.

If you look at Chart B, you can see slowing down a mere ½ knot to “conserve energy” will slow us down quite a bit. With 15 knots of headwind, if we slow down from three knots to 2.5 knots, our actual speed across the water (or “speed made good”) will be approximately one nautical mile per hour. That means that to cover six miles, it will take six hours. Conversely, if we paddle at 3.5 knots, speeding up a half knot from three, we’ll achieve a speed made good closer to two knots. This will put us in camp in three hours, or exactly half the time it took paddling at 2.5 knots.

So the question posed is: who has conserved more energy? One paddler will poke along for six hours. The other will paddle aggressively for three, put up a tent, have a meal, and maybe even take a little nap before the first paddler even arrives.

You decide – plug in different numbers to the table and see what kind of times will be generated by putting in different distances, winds and cruising speeds. You’ll find that when the wind blows in your face, it is almost always better to respond by paddling aggressively, rather than slowing down. The same is true for currents, or any other conditions that may slow your progress.

Clearly, you don’t want to exhaust yourself, but an increase, or decrease in speed of a mere half knot will make a very big difference to the overall time you spend on the water. So sometimes you’ll want to work harder in order to save energy in the long term. Other times, a little math may quickly convince you that avoiding strong headwinds altogether (in favour of staying ashore or modifying your planned route) is by far your best option.

Finally, in my experience, kayakers are very inaccurate when estimating wind speed. We almost always guess that the wind speed is far higher than what it actually is. Get into the habit of looking up wind speed after a day on the water. The internet is great for this. It’s often easy to consult several automated lighthouse reports, so you can get a good “real world” idea of what wind speed you actually encountered. By doing this post-paddling research on a regular basis, you’ll start to have a far better idea of true wind speeds and their effects on the water. I’ve recently acquired a hand-held anemometer and the ability to record wind speeds in my exact location, and in real time, has greatly improved my accuracy in gauging the power of the wind.

Adapted from “Sea Kayaking Rough Waters” by Alex Matthews available at www.helipress.com.