Width and Stability (good article)

[road_warrior64]

Here's a good article about canoe/kayak stability. It makes me think of the Octane models and their reputation for being stable. [url][/http://www.kudzucraft.com/articles/widt ... ity.phpurl]

JC

http://www.kudzucraft.com/articles/width-stablity.php" onclick="window.open(this.href);return false;

[Peter K.]

Actually, looking at the schematics, wider is more stable -- if the width continues the length of the boat. But if one only has a spec sheet with one measurement. .. . .

[ezwater]

I can't tell if your analysis is correct. Which means, for me, it is not useful, and can best be replaced by analysis of the behavior of the boats I actually own.

And, isn't stability mostly a "sissy" issue? A floating rutabaga is as stable as you ought every to require.

[ezwater]

So, where's the highly intelligent Steve Skilling formula? I have a Bluewater, plus several narrower c-1 and k-1 boats.

I have never been able to see what a beginner's impression of stability has to do with eventual success.

[ezwater]

And have you noticed that this is is not a kayaking site, but rather a c-1 and OC-1 site?

Might this suggest to you that perceived "stability" problems for c-1 and OC-1 are not so affected by neurosis as are those for newbie kayakers?

I paddle c-1, OC-1, and kayak, including some markedly "unstable" kayaks like my storied Noah Magma. I just don't see the issue. Just paddle the darned thing.

[JimW]

Hmm, I detect some animosity....

I'm not convinced it's a good article, but I agree with the underlying principle that stability is about more than width (or breadth).

One problem I often see with stability is this:
A wide squared off hullform - say a dumb barge or even a catamaran has huge initial stability, GM is really high, you can move quite large weights around without affecting the heel very much.
But, the range of stability is very low, if you have a heavy load, or perhaps a wave, that tips it to say 20 degrees, it will capsize.
If you have a more ship shaped hull form, rounded bilges flared or tumbled home sides, the initial GM is a lot lower and if you move weights around you really feel the difference, but the rsange of stability is much larger, commonly 60 degrees or more before it will capsize.
Take something like a monohull offshore sailing yacht with a watertight superstructure, GM may be a bit better than a ship because of the ballast in the keel, but having watertight superstructure gives you buoyancy well above deck and it might be possible to heel well past 90 degrees and still have the yacht return to upright, indeed things like lifeboats are designed to be unstable upside down so that a little wave action will tend to make them right themselves.

Now when clients come to me and say "can you tell me how much stability my boat has?" I never quite know where to start......

You can't really quantify stability in an easy way, yes we can calculate areas under righting lever curves but how much should we be looking for? Well it depends on the type of vessel - look into IMO A749, there are some general criteria to apply to ships, but then various different types of vessel have quite different criteria decided by committee to be more suitable for the specific needs of that type of vessel. So for a ship we might be interested in the area under the righting curve between 30 deg and 40 deg or the flooding angle, but for a dumb barge that criterion can never be passed, instead we look at stuff like the ratio of the area under the righting curve to the area under the heeling curve (wind load on deck cargo and barge), or the range of positive stability.

What does any of this have to do with canoes?
Specifically, nothing.
As part of an overall understanding of things, quite a lot.
Depending on the characteristics you want in a canoe you might want different kinds of stability.

For long distance tripping you might want something you move around in without turning it over, so look for something with a flat bottom, squareish sides and generous breadth, but realize that if a wave tips that boat, you have to be dam quick to move to the high side to stop it flipping. For hard whitewater where waves are constantly trying to tip the boat, you might prefer a more rounded and narrow vessel which feels tippier initially but which you can hold upright by merely adjusting the pressure on each knee, and if it does get knocked over really far, which won't put up too much resistance against your low brace recovery....

[pblanc]

I have a very simple definition of stability as it applies to canoes.

Every canoe I have paddled has been "stable".

Until I fall out of it, whereupon it becomes "unstable".

[Bob P]

I have a very simple definition of stability as it applies to canoes.

Every canoe I have paddled has been "stable".

Until I fall out of it, whereupon it becomes "unstable".

Judging by the way my empty canoe runs rapids better without me than with me, I beg to differ.

[chuck naill]

Seems like I used to hear talk of secondary stability. Some of my favorite hulls have smooth tumblehome and lots of rocker.

[ezwater]

Stability is often best understood through comparison of familiar examples, rather than through formulas.

Still, I wish the OP would cough up his Steve Killing formula.

[RobertM]

http://bearmountainboats.com/2012BACKUP ... hnical.htm" onclick="window.open(this.href);return false;

At the bottom of this page is a blurb from Steve Killing describing how the numerical values are generated, and offering some touchy/feely sense of how certain ranges of values feel.

The critical, non-trivial thing here is the metacentric height calculation. https://en.wikipedia.org/wiki/Metacentric_height" onclick="window.open(this.href);return false;

To do a decent job of figuring metacentric height for any complex hull shape is a serious exercise in number crunching involving mathematically taking multiple cross sections of the hull perpendicualr to it's length, and calculating each sections contribution to the overall metacentric height.

If the hull shape can be well enough described, a righting moment as a function of heel angle curve can be generated, which gives some sense of how the transition from upright to heeled over will feel. The math isn't that complicated, but there is a lot of it, and for any of it to be valid, the mathematical descriptionof the hull form has to be right. If it isn't then whatever answer you get is worthless.

There is also an entire secondary argument to be made about whether a high primary stability hull is really a good idea. High primary stability boats don't actually want to stay upright, they want to stay perpendicular to the surface of the water. In large waves this can present a unique set of problems.

[kx250guy]

Stability is overwhelming governed by the physical size
And weight distribution of the paddler.
A 5'6" , 150 lb paddler will feel completely differently in
A certain c1 compared to a 6'1" 230 lb paddler
Who is in the same c1. Especially if he is large
Chested / weight higher , where his power is generated from.
As far as the "sissy" comment goes, why don't
You go work on your technique, and stop making
Infantile remarks.
" Lengthen your on line instead
Of trying to shortening others." Bruce Lee

[ian123]

I don't think the comment was meant to hurt your feelings.

[ezwater]

Yeah, it was. And given my great height, considerable weight, and narrow boat (slalom), I "wrote the book" on everyday practicalities of stability. I'm the unstable one, not you.

The OP needs to put up, now that he hasn't shut up. I would be glad to hear some real ideas.


RobertM--- thanks for adding some real substance.

Showing how a tiny elph can be unstable.......


slowboat by ezwater, on Flickr

[milkman]

When I was first starting out in solo whitewater canoeing, I liked stable canoes like the Dagger Ovation because I didn't have good balance in a canoe or fast, natural counter-reactions to currents affecting a canoe. As I became a more experienced paddler with good balance, I didn't need those training wheels any longer and instead wanted more responsive hulls--canoes that could respond quickly to my every tilt. Thus, based on my experiences, I think initial stability is a great thing for helping beginning canoeists feel comfortable and develop their boat balance with a fewer number of swims. Once they have that balance, boats with little primary stability, but good secondary are the next natural step. To help beginning canoeists develop boat balance and learning to use tilt, I encourage them to do lots of surfing on progressively bigger or more bucky waves.