Buying a Boat
Bottom Lines—Flat, Round, or In-Between?
By
Farwell Forrest
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-between—they 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
is—you guessed it—to take her out for a spin. It's a lot
more fun, too. 'Nuff said.
Copyright © 2001 by Verloren Hoop Productions. All
rights reserved.