i have always wondered how to interpret the seakayakermag test data.

I kind of understand the speed data (ie the less resistance at a given speed the easier to attain that speed) but the stability data sometimes baffles me.

why is the heavier paddler seemingly less stable?

and how does one determine what the secondary stability is from that data?

SK makes the simplifying

assumption (perhaps too simplifying) that the paddler will tilt with the boat. So a heavier paddler puts the center of gravity of the boat/paddler combo higher above the water, thus it tilts further out past the center of bouyancy. This is true unless the heavy paddler carries all their extra weight in lead bars embedded in their backside, anyway.

If the paddler is able to keep their torso vertical while the boat is tipping, it could well change things around. The heavier paddler puts the boat deeper in the water, such that the beam at the waterline is greater. Many variables start to come into play so SK doesn't even go there.

Secondary stability is meant to be represented by the highest part of the graph, but, again, it may not represent real-world performance, it's just a rough indicator. And it's not just the height, but the steepness of the slope leading to it, as well as where it falls along the horizontal line, that all have a bearing on the subjective impression of secondary stability.

SK has a PDF explaining their testing, available on their website.

Mike

found it.

thanks. here’s the link if anyone’s interested.

http://seakayakermag.com/PDFs/Kayak_Reviews_Info.pdf

this sort of clarifies things.

$.02

heavier paddler carries more weight higher up,so the kayak may sit lower in the water but the lever of the paddlers weight against the beam is still greater,heavier paddler = tippier paddler. As the graph shows if you put some extra weight on the floor of the kayak it becomes more stable.

The question about “secondary” is a bit more elusive because it’s really an apples and oranges comparison. Stability is obvious, it’s how high the curve on the graph goes, ‘secondary’ can be interpreted a couple ways by a paddler but it’s not a number describing a resisting force to capsize. A paddlers description of “secondary” could be how controllable the kayak is before OR at the point of capsize. In the case of the kayaks it’s how gentle the top of the curve is and how far the kayak can be taken before capsize . So some kayaks are quite tippy,and can be rolled up and over easily but not exactly what you’d call ‘great secondary!’ Some can be leaned to an edge and brought back easily but aren’t exactly going to dive over in a second. Some could be stable and stiff but go over quickly once the edge is crossed. It’s not something you can see on the graph easily although if you paddle x kayak and y kayak where one feels like it’s ‘got good secondary’ and the other doesn’t the one with “good secondary” will probably have a broader curve. What can’t be shown on a curve is what feels comfortable to you.

very interesting

that the article talks about both the height of the curve (measuerd on the y axis), the distance to the apex (as measured onthe x axis), and the broadness of the top as all influencing secondary stability and the feedback one recieves before capsizing.

comfort

Lee is right that the curve cannot show what is comfortable for an individual.

Maximum heel before instability (indicated on graph) does seem to be an aspect of the secondary/final stability.

In the case of the three boats I mentioned on the thread that gave birth to this thread (Aquanaut, Explorer, Nordkapp), I paddled each before the respective review in Sea Kayaker appeared. I found that the Sea Kayaker observations and stats seemed to be pretty consistent with my experience of each boat.

As a 180lb, 6’, intermediate paddler, my experience of a boat might be closer to the mean to which SK reviews are aimed. Others experience will vary.