I own a perception avatar and a cd sirocco. The sirocco feels pretty unstable. While the avatar feels pretty stable. They both turn about the same. The avatar feels a little faster. So what I want to know is why you would chose an low stability kayak over something pretty stable if all else were equal. I'm a newbie so I keep telling myself that one day I will understand the sirocco's design. Maybe even be glad I bought it. I know! I should of paddled before I bought.What kind of stability
This is something that, until you start doing more off balance stuff like rolling, or go out into waves, is not very clear. But there are two kinds of stability, and in a boat like the Sirrocco you can’t talk about just one because it is intended to be a boat for waves and such conditions. I am not familiar with the Avatar.
Primary stability is how wiggly the boat gets when it is sitting in flat water. Secondary stability is how well the boat tends to return to an upright position once it tipped over a bit onto its side.
Since waves make a boat roll up and down side to side, a boat like the Sirrocco is designed to have stronger secondary stability. That means it’ll get to a certain point tipped over on its side and try to return to an upright position rather than go all the way over.
In waves, primary stability is of at best limited value because the boat is spending most of its time tipped to one side or the other. When you want to stop and take a photo of birds in a calmer situation however, you probably want a boat with high primary stability that’ll stay put while you dig the camera out of your day hatch and focus the shot.
As far as I know, no one has figured out how to design a hull that has both the primary stability of something like a rec or what they call a touring boat these days and the secondary stability of a good sea kayak. So all boats are a compromise between the two, with rec boats being all primary and sea kayaks tending towards more secondary than primary.
If you have a boat designed for dimensional water, it’ll have lighter primary stability and so will wiggle more on flat water. But it is not at all any more likely to actually go over, because it’ll hit its secondary stability and return as long as the paddler doesn’t stiffen up or get into very dicey conditions.
It maybe wouldn’t be desirable anyway, because for rolling and other off balance moves you want a boat that moves somewhat smoothly thru its secondary stability. That heavy duty primary stability and light secondary is part of what can make it difficult to roll a rec boat (as well as the huge cockpits, high decks and poor contact) - it just takes more effort and technical correctness.
That said, the WW boats that are all primary can be super easy to roll - I got into a friends last week and could do all kinds of things that I can’t do in my long boat. But they are quite low decked - you are essentially managing a plastic pancake for many. So they are a real different animal from many of the rec and touring boats in their cockpit fit and height.
Actually, no
– Last Updated: Apr-13-06 7:50 PM EST –
There is only one stability curve for a boat.
Primary stability is the term used to identify the portion of the curve where the righting moment increases as angle of heel increases.
Secondary stability is the term used to identify the portion of the curve where the righting moment decreases as angle of heal increases.
An excellent explaination of stability may be found here:
http://www.guillemot-kayaks.com/guillemot/KayakStability
All very quasi-scientific, but secondary
stability is traditionally taken to mean the degree of resistance to marked heel. I can’t tell from the article for which you provided a link whether they do or do not adhere to the accepted definition of secondary stability. All I can say is that “good” secondary stability refers to a boat that has a marked resistance to further tipping after it has been tipped quite a bit. I have some boats like that. They feel tender when tipped only a little, but provide generous and reassuring support when tipped markedly. My Necky Looksha Sport behaves like that. I have boats with both firm primary and excellent secondary stability (Dagger Zealot slalom c-1), and I have one boat with little primary and little secondary stability. Surprisingly, the latter combination works once you get used to it. You just have to assume active responsibility for the degree of edging in the boat.
A very complicated subject . .
. . and one often poorly understood even by “experienced” paddlers.
mintjulep,
Agreed, there is only one stability curve but the nature of the paddler-boat system means that any static-weight stability curve only tells a small portion of the stability story. Your definition of Initial and Secondary stability do not match the information at Nick’s site nor my own understanding of the definitions as used in the paddling community.
g2d,
In general I agree with your description of the differences between initial and secondary. But remember that our individual impressions of stability are based on personal perceptions and comfort levels relative to edging. Each boat feels different to each different person.
Nick Schade is not prone to fuzzy-math or quasi-science. If memory servers he is trained as a naval architect. Nick’s description of this complicated concept is probably the best I have ever seen published. Half-way down the page he does indeed spell out / explain the classic definition of initial vs secondary stability which is paraphrased below:
Initial stability is normally defined as the stability characteristics (slope of the stability curve) between 0° and 10° of heel.
Secondary stability is normally defined as the stability characteristics (slope of the stability curve) between 10° and the heel angle at the apex of the stability curve.
Newer and even-keel style paddlers tend to prefer higher initial stability profiles. More adventurous paddlers / rough-water paddlers tend to prefer higher secondary stability profiles. Designers build boats with stability curves designed to service the loosely defined preferences of their target market. This often means that boats intended for casual paddling are designed with higher initial stability while those designed for more intensive situations are designed with a preference for secondary stability.
Humm
Jed,
You are right, my definition is not the same as that in Nick’s article. I need to go back and see where I picked my concept from.
I looked in my copy of the naval architecture book used by the US Naval Acadamy, and noted that they do not use the terms “primary” and “secondary” at all in the chapter on stability. The do discuss “initial” stability, as follows:
“The initial slope of the intact statical stability curve indicates the rate at which a righting arm is developed as the ship is heeled over. If the initial slope is large, the righting arm develops rapidly as the ship is heeled over and the ship is said to be “stiff”. A stiff ship will have a short period of roll and react very strongly to external heeling moments. The ship will try to upright itself very quickly and forcefully. If the ship is too stiff, violent accelerations can damage ship structures and be harmful to personnel. If the initial slope is small, the righting arm develops slowly as the ship is heeled over and the ship is said to be “tender”. A tender ship will have a long period of roll and react sluggishly to external heeling moments. Too tender of a ship can compromise stability and leave too little margin for capsizing.”
I agree, the static stability curve only provides a picture of how a boat responds. Response can be very differnent when yo start moving the CG around, as we do when edging. It is difficult to put a good correllation between the quantitative science in the curve and the qualitative “feel” of a boat.
Now throw in Circular wave energy!
And if the definition of stability isn’t complicated enough now throw in the differences in how boats deal with circular wave energy.
It has been written that there is a correlation between boats that have more initial stability (along with wider and flatter hull shapes) being more subject to capsizing in big waves and surf than boats that more secondary (but narrower hulls and less flat hulls).
Thus the situation many group leaders find themselves in when folks buy boats that have great intial stability but then don’t understand that their boat may be quite unstable in big waves.
What I was trying to convey…
Yeah - stability is pictured as a single curve often. And then there is all the other stuff mentioned above.
But… the bottom line that I was trying to get to here was how it would feel, not what is on a chart. This seems to be a paddler who hasn’t had explored or is not yet comfortable with a boat like the Sirocco that will feel more solid in dimensional water than wiggling around on flat stuff. In fact the one thing I didn’t mention that I realized later is exactly what someone else said, that the Sirocco has plenty of stability in the conditions for which it was designed.
That’s the most important thing - that these replies lead to some exploration of edging and a better sense of how solid the boat is, rather than not being able to fully enjoy the boat because of concerns about stability.
what about loading
Correct me if I am wrong, but S and A are different class boats.
The bigger Avatar is under 16 feet, 22.75 beam, with max load of 136kg. Dry storage is listed as 123 liters.
Scirocco is 16’10, 23.5 beam, shallow V, total load volume 375 litres ( that would be eq. to ~375 kg of load). Dry storage 185.
Given the same weight paddler they will feel and behave different, and they do - I am ~150, empty Scirocco felt like a barge.
Why would you ride a motorcycle
when you could drive a car?
When I’m going out to play, I like being able to easily put my boat on edge. Boats that want to be flat feel unresponsive.
As your skills develope
you will probably enjoy a more playful kayak that has lower stability. Learning bracing and rolling skills will open up a whole different world of kayaking challenges. I look at it like riding a bike. When you first started to ride a bike the training wheels feel great and give you the confidense to develope the new skills that it takes to ride a bike. Then come a time when you are ready to take them off and that opens a whole new experience of riding the bike. Once you’ve developed the skills to ride the bike without the training wheels there is no way you would ever ride a bike with training wheels again.
In kayaking a less stable kayak handles very good in rough conditions when the paddler has the right skills. It takes time and persistance to get to this level and it has great rewards.
Too complicated
How I like to think of it and explain it to my students is that primary or initial stability is how a boat feels “initially”. So a boat with strong initial stability will feel very stable. For example, a boat like the CD GTS has a really strong initial stability, but almost no secondary. It feel stable, but doesn’t respond to leaned turns very well and when you put it on it’s edge, it wants to go over. A boat like the NDK Explorer has a weak initial stability and a strong secondary. It wants to pick a side but once it’s one that side it’s like a rock. One reason it’s easier to learn to scull and brace in boats with higher secondary stability.
These explanations are most likely wrong. I don’t care. It is a really easy way to visualize how a boat is actually going to feel and perform. I find it’s easier for beginners to understand the basic concepts when starting out and not bring in discussion of waves vs. calm water and righting curve heel manschweiz cam angles.
no such thing as two stabilties
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Good boat designers do not use the terms primary and secondary stability because they simply don't believe in the concept. Only kayakers seem to want to employ these mystical terms and they spend a lot of time trying to explain to each other what exactly they mean. It's hogwash. It seems to have more to do with feelings than it does with physics. Some boats are more stable than others. Period.
I have two kayaks; a QCC700 and a Pygmy Arctic Tern. The QCC is narrow, long and tender but it is efficient (fast). I leave it at home when the wind is over 15 MPH and usually prefer the more stable Tern. The difference in speed between the two kayaks is much less than the difference in stability and I just get tired of constantly balancing the QCC and looking over my shoulder for those unexpected big rollers. It always depends on what you want to do. If you like to get wet and roll and move as efficiently as you can when yoe ARE upright, get the less stable, narrow kayak. If you like to feel comfy in bigger water, take pictures, surf with more confidence, fish or just plain not focus so much on staying upright, get the more stable boat.
Keyaker…thanks
I agree with your thinking. People get way too anal about terms which are rather unique to sea kayaking. In the end it’s semantics, and however people organize what their feeling into verbage. It’s all jargon, but it works for some, and it really doesn’t matter.
One common belief that I disagree with (one of several) is that tippy boats = expert boats for rough conditions, and that they do better in the rough. I find that incorrect. An expert boater will use the stability in a fuller Chined hull to throw against. For example A Pintail, Romany, Avocet, CH-16, T-165 etc. have enough stability to really throw em on edge and free the ends for fast maneuvering, surfing etc. This becomes harder in a narrower hull with a more rounded cross-section / chine profile. That hull does better in straight-ahead less drag paddling. I think about my old Nordkapp Vs any of the boats mentioned above. The Nordy was great at lond distance high wind heavy sea paddling, but not as maneuverable or fun in Rock gardens, surf etc. Boat geometry has more to do with said boats intended use.
Complicated subject, huh?
I really liked some of the comments in this thread.
To the original poster: What this really shows, I think, is that there is no such things as “if all else were equal” when talking about hull designs which are very different in character. This thread also does a good job of illustrating why lots of folks own a number of different boats, so they can have something close to the “right” boat for a variety of uses.
Now if …
I could get her to read this thread I could buy some more boats!
NIce of you to speak for all good
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boat designers. I am sure they are greatful, every one!
Why did you buy both?
I assume you are using the Avatar as your learning kayak and plan to use the Scirocco more later on? Or was it vice versa?
You said you are new to the sport, and you already have both. I would keep both of them until you have enough butt time to decide that one or both is/are unsuitable for your purposes.
And don’t get hung up on the labels. Just go paddle them!
labels
are tossed around in this forum not so much as an aid to understanding but many times more as a bullhorn to announce someone’s accomplishments. There seems to be a lot of bragging and swaggering and demeaning here. I am sure you know not to let any of that crap bother you. If you can’t roll, or surf or paddle 35 miles a day, so what? Choose the kayak that suits you and your way of enjoying the water and your mood for the day. If the boats are very different, one may be used more than the other. That is my case but I am still glad to have the other less used one.
I can go with that, although WW paddlers
probably use a wider angle for their impression of primary stability. As a heavy person who is very tall above the hip sockets, I can probably tip a boat more easily than most.
C-1 WW paddlers like more primary stability than k-1 WW paddlers… certainly I do… but if a c-1 has plenty of secondary stability, I can adapt to relative absence of primary stability.