Great Kayaks "Insider" - Volume 4/2010

Weight, Drag, Tracking and Performance

This discussion may prove more helpful to long-distance kayakers who would like to maximize efficiency and minimize wasted effort. It should also be of interest to novice expeditioners concerned about how the weight of the vessel plus cargo will affect their kayak's performance.

Assumptions about Weight
Given the popularity of modern ultralight travel philosophies, we've all been exposed

Heavy loaded kayak

to the view that increased weight results in decreased performance. For the sports which pioneered these philosophies (hiking, biking, and canoeing), this view generally holds true. A lighter load in your pack, your bike, or your canoe can dramatically increase your comfort by reducing fatigue and improving performance.

With a lighter load, you can walk, bike, or portage further, maneuver better, and avoid unnecessary strain. The longer you stay at it, the more these benefits add up. Given such positive examples, it seems perfectly natural to assume that the same ultralight thinking applies to the performance of a kayak. Think again! It may come as some surprise, then, to hear that it does not!
That's right, "modern ultralight thinking does not directly apply to a kayak." This may sound unorthodox to those who devote themselves to shaving ounces, but it's the truth. Sometimes, under very specific conditions, a lighter load may yield better performance, but in the case of long-distance touring, a kayak often performs noticeably better under a heavier load, getting you from point A to point B faster, straighter, and with less wasted effort.

Let's consider why. The Partial Truth: Weight is a Drag
Admittedly, there is good reason to believe that an increase in weight will decrease the speed and efficiency of a kayak.

Consider the facts:
Friction ("drag") does reduce a kayak's efficiency. Adding weight does increase the drag a kayak experiences. And, all other things being equal, a kayak which experiences greater drag will paddle slower and less efficiently than a kayak which experiences less drag.
But let's stop to qualify our terms: When we say that a heavier kayak paddles "slower" and "less efficiently," we're talking about actual speed and actual effort at any isolated moment in time. In other words, if we measure "actual speed" and "actual effort" at any particular moment in time, we will almost certainly find that the heavier kayak is technically moving "slower" and requiring "more effort" per stroke. The differences would be small, of course (perhaps 0.1 - 0.3 knots difference in speed) but over an extended period of time, they would undoubtedly add up.
Based on this information, isn't it logical to conclude that the lighter kayak (moving "faster, with less effort") will arrive at its destination sooner? Well, in a word: No. It seems logical, but only because we're ignoring other important variables in the performance equation-the most significant being tracking (how accurately the kayak maintains a straight course).

The Rest of the Story: Heavy Benefits
It sounds counter-intuitive (perhaps that's why you rarely hear anyone admit it), but a heavier kayak often paddles significantly better on an expedition than a lighter kayak, getting you to your destination sooner, with less fatigue. In fact, in all my years of kayaking (regardless of which kayak I've paddled), adding 10 to 20 kilos of expedition gear to my hull has consistently improved my actual progress toward my destination by at least 0.25 knots per hour (as measured by GPS), saving me approximately 30 to 60 minutes over the course of a single 8- to 10-hour paddling day!

How is this possible? Well, to understand it, we have to keep sight of the bigger picture. Yes, it technically takes more effort to accelerate a heavier kayak up to speed. Yes, it technically requires more effort to keep the kayak moving at that speed. Yes, the kayak is technically less efficient when it's loaded with gear. But drag is not the only factor which is affected by weight. There are many other, subtler factors which need to be considered before we can understand how weight affects expedition performance. The first two are interrelated: (1) the nature of kayak propulsion, and (2) the role of momentum.

Kayak Propulsion: A Steady Source of Change

The Tortoise & the Hare Race

If we were talking about a boat with a constant source of propulsion (a motor or sail, for example), and ignoring variables like directional stability (how well the boat maintains a straight course under different loads), we could safely assume that our boat would always travel slower when we add weight to it. Why? Because the extra weight produces extra drag, the extra drag requires more effort to keep in motion, and the loss in effort causes a reduction to actual speed. But kayaks are different.
For one thing, kayaks are propelled by a human paddler. Unlike a motor or sail, a paddler is only an intermittent source of propulsion. When the paddle is moving through the water, it is propelling (accelerating) the kayak just like a motor or sail would do, but between strokes, in that brief moment when one paddle blade is exiting the water and the opposite blade is preparing to enter it, the kayak is no longer being propelled. In fact, the kayak is slowing down (however unnoticeable) because its propulsion has stopped while the surface friction of the water is still hard at work. To exaggerate the image, think of a kayak like a fishing boat with an unreliable motor that keeps racing, then sputtering, racing, then sputtering. The source of propulsion is intermittent; it starts and stops, rather than remaining constant. Even an extremely well-tuned paddling technique (which virtually eliminates the lag time between strokes) is subject to this fact. For the sake of discussion, then, let's say that the paddler is constantly cycling back and forth between two distinct phases: the"propelling phase" (the time the paddle blades are actually moving through the water, propelling the kayak) and the "halting phase" (the time between strokes, when the kayak is slowing down).

Why does this matter?
Because it has a direct bearing on how we understand the role of weight. Although extra weight may offer a consistent disadvantage to a watercraft with a constant source of propulsion, it can actually become a partial advantage for an intermittently propelled craft like a kayak. The secret has to do with momentum. When we say that it takes more effort to accelerate a heavier kayak than it does to accelerate a lighter one, we are talking about inertia: the amount of effort required to put a static (unmoving) load into motion. The heavier the load, the greater its inertia (i.e., resistance to being moved) and subsequently, the more effort it takes to put it into motion. During the "propelling phase" of a paddler's stroke, you must exert greater effort to keep a heavier load in motion. In this regard, it takes "more effort" to propel a heavier kayak. But the story changes dramatically during the "halting phase" of the same paddle stroke. During the "halting phase," the kayak is slowing down because (as I said above) it has momentarily lost its propulsion while friction is still hard at work. At this point, weight can offer an advantage thanks to the power of momentum.

Momentum: The Unstoppable Virtue
Momentum is the opposite of inertia. It's the stored up kinetic energy which tries to keep an object in motion even after it is no longer being propelled. Imagine throwing a heavy bowling ball, but not letting go of the finger holes. What happens? You guessed it: You go tumbling down the bowling lane or get your arm jerked out of its socket! That's momentum! Heavier objects have greater momentum and consequently, a much greater ability to overcome friction. For this reason, a heavier kayak tends to glide further (or slow less) during the "halting phase" of a paddler's stroke. (It also tends to glide straighter.) This is a crucial point because it makes all the difference in the world to how we understand the effects of friction or drag in relation to weight. It proves that the "extra effort" you expend to put the kayak into motion during the "propelling phase" is not necessarily "wasted"; instead, it's stored and released in the form of greater momentum during the "halting phase" of your stroke. Although you expend more effort to propel a heavier load, some of that effort is gained back between strokes when the weight may actually help to keep the kayak moving. It's a small difference, perhaps, but the advantage often increases once you inject typical real-world variables like wind or wave action, which generally do less to slow a heavier kayak (thanks to higher momentum) than they do to slow a lighter one.

The assumption encouraged by modern ultralight philosophies-that "more weight equals a slower, less efficient boat"-fails to recognize this bigger picture. It ignores the many, many other factors which feed into the performance equation and which, in the real world, effectively disprove the claim that a lighter boat will always get you to your destination "faster," with "less effort." True, the heavier boat may cruise a bit slower or require a bit more effort to paddle, but it also maintains a more constant speed, with less fluctuation between strokes.
It's like the old fairy tale about the race between the tortoise and the hare. The overconfident hare keeps stopping, while the tortoise chugs steadily along to win. What was the moral again? Oh yes: "Slow and steady wins the race." In this case, the hare (the lighter kayak) is only slightly faster than the tortoise (the heavier kayak), and the tortoise loses less effort to slowing down and re accelerating. Already, then, the performance gap between them is beginning to close thanks to the realities of intermittent propulsion and momentum. Let's look at just a couple more factors to see why the tortoise very often wins over the long run.

Tracking and Lateral Resistance: The Friction Advantage
Another problem with the assumption that "extra weight is always a drag" is that it

Tracking grooves on the Bamba running the length of the vessel

fails to consider the ways in which friction itself can prove useful. Think about it: Friction does much more than slow you down. It also makes it possible to accelerate (friction provides the resistance against the paddle blades to propel you forward). It also makes it possible to maneuver (friction turns you as you drag your paddle blade or lean your hull to one side). And perhaps most importantly, it makes it possible to paddle in a straight direction (lateral friction converts your off-centered paddling strokes into straight-forward energy). This last kind of friction-the kind that helps you go straight-is what determines a kayak's "tracking ability." Tracking is extremely important, especially during a long-distance paddle. The better a kayak "tracks," the straighter it travels, and consequently, the sooner it arrives at its destination. (Remember, the shortest distance between two points is a straight line.) How well a kayak tracks is largely governed by the length of its waterline. A longer waterline generates greater lateral friction (sideways pressure to keep the kayak from turning or slipping off course), which in turn yields better tracking performance and converts more of the energy in your stroke into straight-forward motion. If lateral friction didn't exist, a paddler's stroke would simply spin the kayak on its own center like a top.

When you add weight to a kayak, the kayak settles increasingly deeper into the water. Lateral friction increases and its waterline grows (how much it grows depends on variables like the amount of taper at the bow and stern, the volume of the kayak, the amount of weight added, and so on). This, in turn, improves tracking. Sometimes the difference is slight, but often it can be quite remarkable. As I said, it depends on many variables. Nonetheless, it is generally true that the tracking ability of virtually any kayak will improve (to greater or lesser extent) when it is loaded with 10, 15, or 20 extra kilos of gear (perhaps even more in the case of a "high volume" kayak). This is assuming, of course, that you do not load the kayak beyond its maximum design capacity, in which case performance might suffer severely.

Now consider the reality that the vast majority of commercially-available touring kayaks are designed to accommodate significantly more weight than that of a typical 6-foot-tall, 75 kg male or (even more dramatically) 5-foot-tall, 55 kg female. Because of this fact, very few paddlers will achieve maximum tracking performance in an empty (unloaded) kayak. Their body weight alone is simply not sufficient to sink the kayak down to its optimal "design water line" (DWL). In fact, I know a number of smaller-framed paddlers whom have to load their kayaks with containers of water to offset weather cocking(the tendency of kayaks to turn upwind because the center of the boat's mass does not match the center of its wind resistance) on windy days. The difference the added weight makes is quite noticeable even to an external observer! Admittedly, in some cases, problems like these are caused by poor buying decisions (the person buys a kayak that simply doesn't "fit"), but in others, they stem from the reality that commercially available kayaks are designed to appeal to a broad audience (which generally means they won't be tailored toward smaller paddlers) or to carry a certain amount of cargo.

The result is that their optimal capacity can be well above that afforded by body weight alone. Why am I telling you this? Because it refutes the simplistic assumption that adding weight to a kayak always degrades its performance or slows its progress. It shows that, in many cases, adding weight to a kayak can improve its long-distance performance by positively affecting other factors which are particularly beneficial during a long-distance trip. Certainly, a lighter kayak will technically be "faster" and require "less effort" to paddle. Certainly, in a short sprint race, a lighter kayak will win almost every time over a heavier one. But thanks to the nature of lateral friction and its effect on tracking, a heavier kayak often performs markedly better across long distances, over longer periods of time. By traveling straighter, the heavier kayak frequently gets you to your destination faster, with less effort. A heavier kayak has a better footprint in the water and, in laymen s terms, it is like "cruising better with an easy paddle"

Taking Advantage of Weight
Despite the complexity of the preceding discussion, the simple fact is that every kayak has an optimal weight range at which it will perform best for a specific paddler, using a specific paddle, with a specific paddling technique. For kayaks designed for long-distance expedition use, this weight range is often much higher than the average paddler's body weight, and possibly even higher than the total weight of gear he (or she) may choose to pack along. Rather than try to master the dense scientific explanation behind this reality, it is much easier (and far more useful) to simply experiment with the way that weight affects your kayak. Try adding and subtracting weight/cargo until you find the ideal weight range that feels best to you. Eventually, you'll discover a winning combination.

fat man

Ironically enough, given the nature of subjective preference, the weight range you prefer may not actually be the weight range which technically yields the "best" performance. (Some people may prefer a boost to initial stability over a boost to efficiency, for example.) Whatever the case, it's important not to lose sight of the big picture (actual progress toward your destination),and to resist the myth that better performance requires you to shed kilos. There's no use laboring to find ways to shave ounces if it turns out your kayak paddles notably better with a heavier load.

If you're truly a die-hard long range paddler, sizing your kayak to your cargo may be the best way to maximize your performance. (Just don't go gaining 10 kilos pounds before your next trip!) For the rest of you, a little careful experimentation with different loads should suffice to help you optimize the performance of the kayak you already own.