initial stability: again....


well just when you think we’ve beat these old stability questions to death, someone has to go and bring it up again…

so the question is: is there a down side to good initial stability in a sea kayak? is the relationship between secondary and primary inverse? such that if primary is high, secondary is low and vise versa? (i know that some of you will say secondary stability is a myth and i think i am growing to appreciate this line of reason).

here is my own experience and why i ask. my Formula Cadence, known by a different name to some of you, has very good initial stability. the boat is also an all around great handling machine. whenever i paddle an NDK Explorer, i notice how much less initial stability it has in comparison. and as we have recently learned here on Pnet, that has something to do with the increased deadrise on that boat. again, makes sense. but is there an advantage to this? from what i can sense, the Explorer is faster edge to edge, which takes some getting used to, it is ‘twitchy’ compared to the Cadence, and most kayaks i have paddled. this edge to edge quality may offer a handling advantage providing a skilled paddler, a more precise and nimble ride. MAY, is the qualifier here. one may get this quality in other boats, which don’t feel as ‘twitchy’ as an Explorer does to me. since i haven’t paddled all the boats in the world, my experience is limited and leaves me wanting.

so, dear pnetters, and pnutters, please expound on this topic and help me get some further insight so as to these important questions of the universe.

your insight and wisdom is appreciated.

No such thing as secondary? Think I’ll just let that go and suggest you consider the idea of static and dynamic stability instead of initial and secondary.

Static (initial) stability is about the boat staying flat to the water (static). In waves - if the kayak is flat to the face of the wave you are tipping over! Yes you can have too much of that.

You want to stay upright on tilted water. That’s where dynamic (secondary) stability is more important. The ability of the boat to be leaned and edged dynamically. To be controllable at various angles to the water (heel) so you can remain upright and your center of gravity over the center of buoyancy - which is easier to do in a dynamically stable (good secondary) hull than one that is statically stable. You have to be able to work this though.

All boats are some sort of compromise/blend of the two.

Greyak Is Right, (hum again)
I am still in the learning stages and in fact have picked up several pointers from Greyak along the way.

Initial stability is the measure of a boats resistance to tipping from a resting position. Paddling a kayak is differant as compared to other boats. In a kayak when paddling in what paddlers call textured water, water with waves, you want the kayak to float over the wave and pivot around your waist. You will be vertical and the yak will follow the surface of the water. The boats ability to do this depends on some level of initial stability, or in-stability. As you progress into using the position of the yak to assit in making turns and handling more textured water you and your yak will use the intial stability. Secondary stability becomes important as the boat will resist capsizing once leaned over to carve a turn or flex over a wave.

Happy paddling,


Relationship between
"Is the relationship between secondary and primary inverse? "

Though someone, somewhere may have come up with a boat that has both very strong primary and very strong secondary stability, as far as I know the boats that are available will have more of one and less of the other. And in waves or any other dimensional surface, as Greyak has explained very well, the thing that will keep you up is the secondary. The bumpier things get, the less time your boat is spending in any position where primary stability will serve you.

When Sea Kayaker reviews a boat, they are recording what we talk about as secondary stability when they measure degrees of heel. Anyone who thinks that secondary is a myth should review that material - or talk to anyone who owns a sailboat designed to run at 45 degrees of heel.

As to your boats… I have an Explorer LV and have what may be bad news for you. As far as I know, the Explorer has about the highest primary stability relative to its secondary of any full length sea kayak out there. And it has darned impressive secondary - so you may want to get accustomed to that boat before trying out any really dicey ones.

Until you are an advanced paddler

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you cannot know what would give advantage to one.

One day I will be an advanced paddler. Those who say secondary is a myth should edge a surfboard on calm water.

This is the last time I will write this. As a young child I used to ride my bike on a 40 degree slanted curb. since the bike essentially has no primary stability, once you have made the adjustment to riding on a slanted surface you have no problem continuing, If the bike had training wheels (massive primary stability) you would have to get up out of the saddle and off on one side to ride that curb. That would be inefficient and impossible to do for any distance.

Paddling in Beam seas is analogous to riding the bike along that slanted curb.

The kayak and paddler are a system. Look at the boat by itself doesn’t tell the whole story.

For example, I’d never consider an Explorer to be “twitchy”. For me it’s a very comfortable, relaxing boat.

definitions not required thanks.
i have worked as a manager and trainer for years with canoes and kayaks, have paddled them for many more. if you read my post, i am not unclear about the definitions regarding these concepts. and by the by, nice dig Peter.

have paddled many squirrley boats Celia, from many OC1’s and C1’s, to skinny stich and glues, and given my size, the std Explorer does not exhibit the stability curve that you describe in my experience. certainly not in comparison to the Cadence- the direct comparison drawn in my example.

"The kayak and paddler are a system."
Angsrom is right. The Sea Kayaker stability curves are given at various loads. A look at any one of these charts makes the variance according to load obvious.

I find the NDK Explorer to have astoundingly high primary stability. I find it kind of leaden (boring) on flat water. Indeed, in my experience the Explorer and Romany have about the highest primary stability of any boats with such high secondary.

I like active hulls, hence my choice of an Aquanaut as my primary boat. Yet, I find a Silhouette a bit unnerving (I believe, and Nigel Foster agreed, that I am too big for the boat.)

Explorer Stabilities

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Agreed, any boat's stabilities are tested assuming certain weight ranges. In my case, since the LV is still the original Explorer hull and I am not a 180 pound guy, I have to load up weight to make it hold an edge without muscle work on my part. So for any skills work where I need to hold an edge for a time period, I have to load at least 40 pounds into the boat to give my thighs a rest.

If someone were over the expected weight or size, things would go in the opposite direction. Though, you'd have to be a pretty good-sized person to overweight the Explorer.

Maybe a question that I should have asked - I am (obviously) relatively unfamilar with the other boats you mention, but it just occurred to me that talking about just stability may not really be it. One thing that I found to be very different and somewhat unnerving when I first got the LV was its behavior in following seas or confused conditions. My prior boat had a lot less rocker and ran real straight, so responded pretty stffly to that stuff and tended to bob up and down more than slide around the side of waves. So the tendency of the LV to want to turn around seemingly at the drop of a hat took some getting used to. I wasn't concerned about flipping over, but getting comfy with the LV's loose bow and willingness to change direction in conditions took a little time. It was just a real different way of handling snotty conditions than I was accustomed to.

Why all the hubub?
Of course secondary stability is real. I can see where it would not be of any concern to flat water paddlers, but should be very real to the rest of us…even flat water paddlers that edge to turn. Hull designs tend to work roughly on land as they do on water as Peter pointed out. Anyway, here’s a few “extreme” hull shapes to show how secondary stability really does exist:

Circle: Equally stable on any point of its axis. If primary and secondary didn’t exist, we’d all be paddling barrels and torpedoes.

Square: Great stability on its bottom or sides, like a canoe with lots of tumblehome. Of course, an oval might be more fitting here.

Rectangle: Much greater stability on its bottom than its sides, like a recreational canoe or kayak.

Triangle, point up: Great stability on its bottom, ok stability on its sides with a definite “flop” effect over its chines, like a surf kayak.

Triangle, point down: Low stability on its bottom, great stability on its sides, like a Baidarka or Greenland style kayak.

Plaining hull whitewater canoes and kayaks are probably most like pentagrams with one point up, but now it’s getting complicated.

There will always be exceptions to rules of course. For instance, a pane of glass should have great initial stability lying flat on water. However, there is no buoyancy through any of it. So it has relative neutral stability in any orientation. Also, hull shapes can and do react differently depending on where the center of balance is.


OK, what type of stabilty is needed…
… for trolling!

Hey jbv why ask the question if you

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know the answer? Any one who has a basic understanding of primary stability (like,... can read the descriptions in sea kayaker) would know that the upside to is is the ability to relax n calmer water and that the downside to it is that the same righting force becomes tipping force in a beam sea. This is published near ever stability chart in sea kayaker magazine!

Was the dig the thing about the surfboard? The argument that secondary is a myth seems to suffer in the light of that example. I did not see you advancing that argument though I did see you slipping toward the slope of that pit of unreason.

If it was my remark about wanting to be an advanced paddler one day; hey that's true. Got a problem with the fact that I capsize all the time and that my forward stroke needs work? OK have a problem. (I don't often take the time to read profiles, but now that I've read yours; Yes I do wonder how an advanced paddler can ask this question: "is there a down side to good initial stability in a sea kayak?"

It seems to be the fashion to ask a basic question, (like is there a down side to good initial stability in a sea kayak, or why a $1000 drysuit and then totally diss those who answer. Hope you are enjoying yourself.

Here's more answer for you.

Round bottom hulls are (in general faster than hulls which offer more primary stability. Of course you have to allow for the fact that a fair amount of energy will be spent balancing and bracing a round hulled boat. As a design moves away from round hulls it should become more stable. If the roundness became a shallow arch then there will be a great increase in primary. If the roundness became a razor V instead the secondary will increase. So we see an inverse relationship between speed and stability. This is another dowmnside to higher initail stability

I find the explorer to have less primary stability than, say, the aquanaut. I weigh 220. I would much rather be in my explorer than in my old caribou in rough water though the caribou has much more initial stability. I weigh 230 with short legs a log torso and a lot of weight in the shoulders. If I weighed 170 I would never have sold the caribou.

Everyone knows the answer
about primary stability and waves, but I’m with jbv in being a little skeptical about whether that answer is right, or at least whether it’s meaningful within the range of kayak beams (say 17-30 inches or so). Even a very wide kayak hull (e.g. my barge-like OK Cabo tandem) is narrow enough to be perfectly manageable in active water, and it’s a whole lot easier to stay on in that stuff than a very narrow, highly responsive hull (e.g. Mako Millenium).

What does make a huge difference is how the hull responds as it starts to lean. It’s certainly true that wide, flat-bottomed, square-sided boats are nasty in waves, but IMHO that’s because the flat bottom and square sides create a really ugly transition between squarely right side up and squarely upside down, not because of excessive primary stability per se.

good point
My objection to the boats I’ve tried with “too much” primary is that I can’t get them on edge when I want to, and if I can edge them I have no idea what they’ll do next. A smooth transition and good manners on edge would be a big help.

Some of it’s just a matter of taste – if the boat is too stable I feel more like a passenger than a participant. Must be all those hours sailing a Sunfish as a kid…

I’m not trying to pick a fight here or anything, it’s just slowly grown on me over time that the conventional explanation of why sea kayaks behave better than rec boats in waves is a little off, and that comparing the hull shapes of rec boats with some SOTs (with beams in the rec boat range but hull shapes closer in some ways to sea kayaks) offers some clues as to where it’s off.

squarely right side up…
…, or squarely upside down, pretty much defines initial stability.

The transitions and flip point is key though for how much is too much or too little of either - and what we actually deal with. Varies by paddler and conditions too.

My Tarpon was pretty hard to flip - but when it did it went fast. Stayed upside down well too! My SINK offers a lot more variety of angles it’s happy at, giving me more options.

Can’t speak for the technical
Can’t speak for the technical aspects but I bought an Explorer HV three years ago. My previous boat was a Necky Tesla which is 25" wide with lots of primary stability. Too much, I found out because this was my first boat.

The Explorer felt twitchy when I got it but now it doesn’t. Less primary stability is easier to paddle in waves, and easier to put on edge. It has great secondary as well, so it stays on edge very well. You’ll get used to it.

aren’t about how much primary stability is too much, but about how a hull design that maximizes primary stability for a given beam is likely to have little or no secondary stability and an ugly transition from right side up to swimming.

I’m not trying to sell anyone on high primary stability. I agree that lower primary stability is often part of an attractive set of handling characteristics. Where my comments are coming from is my own thought process of trying to reconcile the conventional wisdom that wide beam and high primary stability are bad in waves with my own experience in wide-beamed, stable SOTs that are very easy to paddle in waves (the Scupper especially, but even the Cabo; my old Cobra Expedition was more the flat-bottomed, square-sided shape with an abrupt transition to upside down). I think that conventional wisdom comes from comparing rec boat hulls to sea kayak hulls, and I think it’s a bit off for the reasons I’ve stated.

I Just Know What I Like
I prefer a low-in-the-water, stable feel. I know some of the “twitchy” feel is related to volume. In a Tempest 170 I bob around 'cause I only weigh 165 pounds and carry minimal gear (Day Tripper yeah) In a Tempest 165 the bobber feel goes away. Much more stable, initially.

I thought I would experience the same thing with the QCC boats. I didn’t. I felt nearly as “twitchy” in a QCC600 as in a 700. I guess hull shape is more of a factor here than just volume?

600 feels twitchier to me to. Sort of oppostive of your 165/170 thing. I may sink the 600 a bit deeper - but that doesn’t make it steadier. The extra length on the 700 = more stability for me.

Funny how impression of twitichy changes over time too. I’d consider both to be pretty rock solid now. I can be very lazy/relaxed in them.

The Nordkapp with padded up foam seat I tried Sunday had less initial, but I couldn’t even really call it tippy either. Definitely more “active” and took more effort - also felt like it needed a lot more weight, and I’m not light, and would be happier loaded to the gills an in rougher water. 170 I tried was crazy stable. Both seem short to me. The bob around a lot compared to the 700 with it’s long waterline.