Buying a Boat
Bottom LinesFlat, Round, or In-Between?
What shape is your bottom? No, I'm not getting personal. If you own a canoe or kayak, you'll probably know the answer to this question already, but if you're in the market for your first boat, you'll need to learn the language. Not all bottoms are alike. Some are flat. Some are more or less round. And some look like the letter "V."
Why is this important? As I've noted elsewhere, when stripped to its essential elements, a canoe or kayak is just a device for displacing water. How it displaces that water will affect its performance and handling qualities. Take a flat-bottomed boat, for example. It makes a uniform hole in the water. Viewed in cross-section, no one point on the bottom will be deeper than any other. From keel (mid-line) to chine (the point where the bottom joins the side), every square inch of surface carries the largest possible share of the total weight. The result? A flat-bottomed boat draws less water for a given load than any other type of comparable size. It also feels very stable.
Now consider round-bottomed craft. Few canoe or kayak hulls are truly round, of course. Most are best described as rounded (or "shallow-arch"), instead. If you've ever tried log-rolling, you'll know why. A true round-bottomed boat wouldn't be very stable. You'd have to work mighty hard to keep it upright. On the other hand, even gently-rounded hulls have less immersed surface area for a given volume than any other type. And since surface area generates drag when moving through the water, round-bottomed boats are faster than others.
Many boats are neither round nor flat. Their bottoms come to a point, instead, and their cross-sections resemble a shallow vee. This "point" serves the same purpose as the fin keel that you can still find on some aluminum boats. It helps you go straight. Since most paddlers want to go straight most of the time, this is a good thing. (You won't find a keel on a whitewater playboat, however! Not everyone wants to go straight.) The vee has another advantage, too. When leaned to either side, a vee-bottomed boat settles down on a flat surface. It starts to resemble a flat-bottomed boat, in other words, and it exhibits some of the same comforting stability.
The bottom line? All other things being equal, flat-bottomed boats are slow but stable, round-bottom boats are fast but tippy, and vee-bottomed boats come in somewhere in-betweenthey feel a bit tippy at first, but they become more stable, or "stiffen up," when leaned. Of course most of us serious paddlers would be embarrassed to use words like "tippy." If we're old salts, we may say that such boats are "tender," but if we want to go the whole hog, we'll say that they "display a high degree of primary stability." By contrast, any boat which stiffens up when leaned is said to exhibit "good secondary stability."
One more thing. In looking at kayaks, it's important to remember that kayakers sometimes hang around in their boats when they're upside down. This is essential in performing the so-called "Eskimo roll," a useful technique for righting a capsized kayak without bailing out. When a kayak's upside down, though, its deck becomes its hull. You don't want your kayak to be too stable when it's inverted. So take a close look at the deck on any touring boat you're thinking of buying. Uniformly flat decks won't help you roll, and they don't do much for your carrying capacity, either.
Confused? Don't be. All these differences are pretty subtle, and you won't be able to tell much if you only look at a boat's bottom. The best way to find out whether a canoe or kayak is tender or stiff isyou guessed itto take her out for a spin. It's a lot more fun, too. 'Nuff said.
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