Where's the keel?

May 28, 2005 5:34 AM

I've almost always toured in an aluminum canoe. I don't like the noise (or the weight) but I like the tracking and stability afforded by the keel, especially in a big wind on a big lake. Why don't kevlar/royalex/etc. touring canoes have keels?
posted by bricoleur to sports, hobbies, & recreation (14 comments total)

Pedantic answer:

They do actually have keels-- the keel is the line of symmetry for the canoe whether there's a raised seam or not.

Answer in the spirit of your question:

Because they don't need one. That raised keel is there because it's covering the point where two pieces of aluminum are riveted together-- partially for aesthetics but mostly to protect that seam from rocks etc. It's not there to aid stability and it doesn't do that to any measurable extent. If a raised keel was an actual benefit, royalex touring canoes would have one molded in. Royalex/kevlar canoes don't have a keel because they're molded from a single piece and therefore don't need one. Mixed use canoes still wouldn't because it would add to the displacement.

I find aluminum canoes much harder to control than royalex ones. You find them easier. You say that you mostly have used aluminum. I have mostly used royalex. We know they handle differently because we both have a preference. I'm betting that this has nothing to do with a keel-- you get better tracking and stability from what you're used to!

Neat question. We need more canoe talk here.
posted by Mayor Curley at 7:11 AM on May 28, 2005

maybe the stability comes from the weight?
posted by andrew cooke at 8:00 AM on May 28, 2005

Mayor Curley:

Pedantic response to pedantic answer: The line of symmetry to which you refer is the "keel line." A keel is an actual structural member, and I've never seen one in either a kevlar or a royalex. True, a keel does not necessarily extend below the hull, but the word "keel" is commonly used to mean just that, e.g., "A projection below the hull running from stern to bow, which helps the craft maintain straight movement."

Response in the spirit of your answer:

It's not there to aid stability and it doesn't do that to any measurable extent.

If it were only there to protect the center seam, it could just as easily be flat. Next time you see an aluminum canoe, have a look. The keel is actually a "T" in cross-section, and is clearly designed to make the canoe track better on open water. It also makes the canoe less susceptible to rolling when lightly loaded.

No doubt I could practice and get more adjusted to the handling of a keel-less canoe, but I'm wondering why I can't have my cake and eat it too.

andrew cooke:

There's not enough difference in weight between an aluminum canoe and a royalex canoe to affect the handling. The weight is only an issue with respect to portaging. When you're carrying your gear over a rocky, swampy half-mile to the next lake, 20 lbs. can make a big difference. So it's a trade-off: Skittish on the water, but light on the portage; or stable on the water, but heavy on the portage.
posted by bricoleur at 8:19 AM on May 28, 2005

The aluminum keel is likely not helping your boat track straighter, but it is certainly slowing you down.

Here's an article on Canoe design from a Nautical Engineer. (From my the only canoe manufacturer I know that uses computational fluid dynamics to design their boats.) Excerpt on course stability:

For most paddlers, simply maintaining a straight course is challenge enough and any canoe that does so with minimal effort is a blessing. The following are general guidelines in improving course stability;

Course stability improves with:
A lower block coefficient (CB)
Increased L/B ratio (Length to Beam -PE)
Stern-down trim (Moving weight to the back -PE)
Increased hull profile aft (A boat with a deeper draft at the stern -PE)
Increased L/H ratio (Length to draft)

Course stability is slightly affected by:
Location of LCB (The point of widest beam I think -PE)
Mid-section shape.
Waterline shape
CP within normal limits. (The center of pressure. By within normal limits, I think he means fairly close to the center of gravity, or CG -PE)
Since turning is the result of moments acting about the CG, controlling these moments is the method by which course stability is achieved. This control is a function of hull shape, how it is presented to the water flow, weight movement, and paddle actions. Because a canoe is so easily trimmed fore and aft and athwartships, trim is a valuable tool in improving controllability. Altering the hull shape with heel, trim of both can offset the turning moments caused by off-center power application, wind or waves.

Mayor Curly: Neat question. We need more canoe talk here.
hear hear.
posted by Popular Ethics at 8:45 AM on May 28, 2005

"Skittish on the water, but light on the portage; It has been many years since I went canoeing but we always went for the lightest canoe and carried two small bits of rope and a small hatchet and built a light outrigger for stability.
posted by arse_hat at 8:56 AM on May 28, 2005

Most kevlar and plastic canoes are constructed with a gently v-shaped hull, which essentially acts like a keel to keep the canoe moving in more of a straight line.

A lot of the lighter canoes are actually built for quicker and easier maneuverability. If you're paddling down a twisty river or through some dodgy rapids, you want the canoe to be able to turn easily and at a moments notice.

If you're planning to sit and fish, and not planning to portage, then by all means get the heaviest canoe you can find. In fact, skip the canoe altogether and go for a small aluminum boat. They're made for exactly that kind of thing, and will be much more stable and less likely to drift around than any canoe.

I've tried all different kinds of canoes and the kevlar canoes are far and away the best for all kinds of travel, especially for strong paddlers with good steering skills. In high wind conditions, a kevlar canoe's lower profile keeps it from getting blown around a lot more than some aluminum behemoth that rides much higher in the water.

Of course Kevlar canoes cost five times as much as aluminum ones. That's how it goes with high-end technology in any field, though. Imagine you've been driving a schoolbus all your life and you get a chance to try out a ferrari. It's like that.
posted by bonheur at 9:24 AM on May 28, 2005

You are doing a j-stroke (or variant), yes?
posted by docgonzo at 11:34 AM on May 28, 2005

OK, guys. Good input, and I thank you. And yes, by all means, more paddling talk!

But...you're not answering my question. You're trying to convince me I don't need a keel, and that I'd be happier in a kevlar canoe without one. My question was why, if I'm convinced I want a keel, can't I get a kevlar canoe with one?

For the record, I've tripped in aluminum, royalex, and kevlar canoes. As I've said, I still prefer the aluminum, in spite of its weight, noise, and flashiness, because dammit, it tracks straighter. Try paddling across a big bay, in a big wind, in a well-trimmed kevlar canoe. Yes, you have a lower profile—which means water coming in over the gunwales. And you are constantly correcting your course. Now try it in the same conditions, in a well-trimmed aluminum canoe. You can spend your energy creating forward motion. A smooth hull is great for river running, because it will turn on a dime. That's a liability on a lake.

Frankly, I'm beginning to suspect that none of you have actually paddled an aluminum canoe.

And yes, for heaven's sake, I use a j-stroke—when appropriate.
posted by bricoleur at 2:23 PM on May 28, 2005

Bricoleur-- I suspect another reason that Kevlar canoes don't have keels is that most people purchasing one want the absolute lightest canoe possible. Anything additional adds weight, and those canoes have been engineered to be as lightweight as possible. That said, if you want a Kevlar canoe with a keel talk to Mad River or another manufacturer about getting one added aftermarket. I'm sure it's possible, for a price. I think you'll still find that because of the lighter weight and lower profile, the kevlar canoe won't behave EXACTLY like an aluminum canoe on the water. It sounds like aluminum meets your needs pretty well, you're used to it, you're attached to it, and you're not willing to make any concessions. Why not just stick with what you've got?
posted by bonheur at 2:41 PM on May 28, 2005

P.S. I understand the feeling of wanting to expend your energy on creating forward motion and not working to keep a straight course, but it's been my (extensive) experience that kevlar canoes (my experience is limited to the Mad River explorer, Wenonah MN II, and various solo canoes) travel significantly faster than either Royalex or aluminum. Stage a race and see for yourself. Anyhow, it's okay to prefer paddling an aluminum canoe. Lots of people do.
posted by bonheur at 2:45 PM on May 28, 2005

In the past I spent many years racing canoes professionally and also building them. I know what you're saying about noisy aluminum boats. We call them boominum canoes.

Curley is correct. The keel on aluminum canoes is there for structural purposes, not directional stability. Without the keel piece serving as an I-beam, the bottom would oil-can and cave in. Composite canoes do not require a keel for stiffness. Directional stability in a canoe is achieved by having an absolutely straight hull line from bow to stern -- the ends do not curve up. This is known as rocker. If you set a whitewater canoe on the ground, you can rock it end for end like a rocking chair. This rocker allows it to maneuver and turn easily. A cruiser on the other hand will touch the ground from stem to stern.

This lack of rocker, not a keel, is what gives a canoe tracking stability. The longer and less rocker in the hull line, the straighter (and faster) the boat will go. The worst condition for a canoe is a strong cross wind. A canoe tracks just like driving a car in reverse at high speed. If you try to do that you will find that the fixed wheels try to go straight, but the steering wheels swerve back and forth. In a canoe, the bow tries to go straight, but the stern tends to slide around and that is why the sternman does the steering. In a cross wind, this means that the wind has little effect on the bow, but the stern slides away from the wind. This causes the canoe to weathercock and point into the wind. The person in the stern has to work very hard to push the stern back to the windward side in order to maintain a cross wind course.

Rocker should not be confused with the shape of the cross-section which is at right angles to the length. Most aluminum canoes have a very flat cross-section. A flat bottom provides good lateral stability in calm water and makes a good platform for fishing. However a flat bottom is very unstable in rough water. If a wave comes from the side, the flat bottom will tilt to match the steepness of the wave and easily overturn the boat. A canoe with a more rounded bottom, on the other hand, will remain vertical. The bottom does not tilt on the face of the wave. The other advantage of a rounded bottom is speed. A round shape has less surface area and therefore less drag than a flat, boxy shape.

You should get over the idea that a keel is required for directional stability. That little bit of keel in an aluminum boat has little effect (other than psychological) on going straight. Length of the canoe and the amount of rocker control directional stability. You should try a composite canoe that has zero rocker and is at least 18 feet long. You may have had a bad experience with a composite boat with too much rocker that is meant more for whitewater maneuverability than for cruising.

One thing that aluminum keel is good for is catching rocks. This is very dangerous in whitewater and can easily flip a boat. At one time Grumman used to offer what they called a shoe keel for whitewater. All they did was take the keel and put it on the inside of the canoe since it was still required for stiffness but there was less on the outside to catch rocks
posted by JackFlash at 3:27 PM on May 28, 2005

OK, maybe I am an old fart.

I'm going to try kevlar again, making sure it's rockerless (thanks JackFlash). And every time it feels like it's scooting out from under me, I'll just tell myself that's how it should feel.

'Cause carrying even a lightweight aluminum is getting to be a bit much, and the sound of a metal stringer in the floor of a Grumman at five o'clock in the morning just sets my teeth on edge.

Thanks for the education, guys! (And my apologies for doubting you, Mayor Curley.)
posted by bricoleur at 2:48 AM on May 29, 2005

Why don't you get in a kayak already?
posted by atchafalaya at 9:02 PM on May 29, 2005

Why don't you get in a kayak already?

I've got nothing against kayaks, but they don't seem too practical for lake-chain tripping. From what I've seen, the guy in the kayak will get to the portage ahead of the guy in the canoe, but then the canoe guy just grabs his stuff and goes, while the kayak guy spends the rest of the day taking his gear out of little compartments, schlepping all those little packages over the portage, and then putting everything back in those little compartments... I don't have that kind of patience.
posted by bricoleur at 9:37 AM on May 30, 2005