Weight, Drag, and Performance
by Wes Kisting
In my editorial The Weight of Myth, I considered how myth and misinformation can cause poor or dangerous advice to circulate in the online kayaking community. To demonstrate the nature and magnitude of the problem, I analyzed an article entitled "The Lightweight Secret" and dissected the author's problematic claims about the relationship between weight and performance. What began as an "example" quickly grew into a detailed discussion of weight in relation to drag, momentum, and tracking.
This discussion may prove 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 cargo will affect their kayak's performance. The article that follows is very similar to the original discussion of weight which appeared in The Weight of Myth, but revised to reflect a more specific focus on the practical effects of weight.
Heavy Assumptions about Weight
Given the immense popularity of modern ultralight travel philosophies, we've all been exposed 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. It may come as some surprise, then, to hear that it does not.
That's right, I said "modern ultralight thinking does not directly apply to a kayak." This may sound like heresy 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:
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 equationthe most signficant 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 20 to 40 pounds 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
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 unnoticeably) 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 philosophiesthat "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 reaccelerating. 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 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 frictionthe kind that helps you go straightis what determines a kayak's "tracking ability." Tracking is extremely important, especially during a long-distance expedition. The better that 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 20, 30, or 40 extra pounds 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 (and, in fact, a good number of the kits and plans available to home kayak builders) are designed to accommodate significantly more weight than that of a typical 6-foot-tall, 170-pound male or (even more dramatically) 5-foot-tall, 125-pound 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 two smaller-framed paddlers (both female) who have to load their low-volume kayaks with gallon-jugs of water to offset weathercocking 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 long periods of time. By traveling straighter, the heavier kayak frequently gets you to your destination faster, with less effort.
Let's consider how a tracking penalty of just a single degree would affect a hypothetical paddler who paddles non-stop, at a constant rate of speed, for 8 hours (480 minutes). In the figure shown below (not drawn to scale), Kayak One (blue) travels straight from point A to point B, whereas Kayak Two (red) deviates off-course by just one degree, and then turns straight toward its destination at the end (x = time lost to course deviation). All other factors being equal, Kayak Two will lose 8 minutes and 23 seconds to course corrections by the end of 8 hours!
Even with a GPS, the paddler of Kayak Two would probably never notice he has deviated off course. It's hard enough to see the difference in trajectory on paper (when the one-degree angle is drawn to scale), let alone in practice, when the kayak isn't erring conveniently in one direction. (A real paddler would "zig-zag" imperceptibly toward his destination.) Nonetheless, the tiny penalty to tracking adds up to an extra 8 minutes and 23 seconds on the water! Now consider the reality that an empty or lightly-loaded kayak might easily suffer a two-, three-, or four-degree penalty to tracking (still barely perceptible even on GPS). Over an eight hour period, the lighter kayak will lose approximately 17 to 25 minutes (possibly more) to course-correcting efforts. Add in real-world variables like wind and waves (which typically exert a greater disruptive influence on a lighter kayak) and the advantage of weight should increase still further.
Regardless, the point is clear: The extra effort required to propel a heavier kayak is often (though not always) more than compensated for by a reduced tendency to deviate off-course, a higher resistance to the effects of wind and waves, a less frequent need for corrective strokes, and a shorter (because straighter) distance traveled from point A to point B.
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 cargo until you find the ideal weight range that feels best to you. Eventually, you'll discover a winning combination.
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 pounds. There's no use laboring to find ways to shave ounces if it turns out your kayak paddles notably better with a heavier load.
Having said that, there is one way in which you can cut weight and maximize performance: By sizing your kayak to fit the particular weight range you expect to carry. Here's how it's done:
Based on the sample numbers provided, the ideal kayak would have a "design waterline" calculated to carry approximately 265 pounds: 180 lbs. paddler + 10 lbs. of gear + 30 lbs. "wiggle room" + 45 lbs. for the weight of the kayak itself = 265 pounds.) By choosing a kayak designed to carry an ideal capacity close to this number, you should be able to exploit the advantages of reduced weight (less "drag") without suffering the penalties to directional stability which favor a heavier kayak. (Realize, however, that this performance advantage may come at the cost of a much wetter ride in heavy seas compared to a kayak with more reserve buoyancy.)
If you're truly a die-hard expeditioner, sizing your kayak to your cargo may be the best way to maximize your performance. (Just don't go gaining 20 pounds before your next trip!) For the rest of you, a little careful experimentation with different loads should suffice to help you optimize the long-distance performance of the kayak you already own.
Check the Facts
© 2006, Wesley Kisting