Kayak Stability

I know nothing about kayak design....I just enjoy building and paddling them. I have a question on kayak stability. I have 2 identical CH16's. A friend and I paddled them yesterday in some confused water with 4 - 5 foot chop in a stiff northeast wind. I'm 5'8" - 140lbs. My friend is a touch over 6' and probably 50lbs heavier than I am but very fit. He has more paddling experience/training than I have. Upon launching he immediately commented on feeling unstable in the chop as the waves were hitting us broadside as we tracked to our destination. He also commented on how stable I looked as the waves rolled under me. I was completely comfortable (surprising as I suffer greatly from motion sickness) and I experienced no instability at all.

20 minutes into our trip he capsized in a trough. We made it to shore safely and never felt that we were in any real danger. Neither kayak is outfitted with hip or knee braces.

I know the paddler's size/weight affects the stability of a kayak but how does all this work in the conditions that we experienced yesterday combined with the kayak's design? Something I'd like to consider before choosing my next build.


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RE: Kayak Stability

Well, for starters, taller heavier guys carry their weight higher than shorter lighter ones, so they're center of gravity is higher. A low CG is more stable than a high one, so that's probably the biggest factor here.

The taller folks also have more "sail" area up higher, so their center of effort is higher. Again, a low CE is more stable than a high one, so your poor friend was doubly disadvantaged.

A third possible problem is the period of the waves. Every kayak/paddler/cargo combination has a characteristic bouncing frequency. This is caused by the weight of the boat/paddler pushing the hull down and water pushing it back up. If the frequency of the waves matches the frequency of the boat, mechanical resonance can amplify the motion and take the boat beyond its stability points, especially if the motion on one axis couples dynamically with another (easy to do in pitching, rolling waves).

Finally, paddlers who feel these sensations may try to correct for them and misjudge, making the situation worse. This can be caused by loss of coordination caused by seasickness, unfamiliarity or fear.

Kayaks & their paddlers are a dynamic system interacting with the marine environment. Stability is a complex interaction between all the components. if one gets too far out of whack - splash.



RE: Kayak Stability

Thanks Laszlo.  It all makes sense….but how do taller/heavier paddlers best compensate for their higher CG/CE especially when paddling less stable models like say a Petrel in choppy waters?  Is it just practice and skill?  Are they less efficient paddlers?  I would have thought that a heavier paddler would have a ballast advantage in choppy waters but your CE explanation clears that up.   Your comments on wave action are interesting too.  I kayak on Lake St. Clair which is a good size but very shallow.  When a northeast wind blows beyond 10 knots it really messes up the water on the Canadian side with high waves in quick succession – almost like surf but in the middle of the lake. So many things to consider when choosing a design…. Thanks again. Chris

RE: Kayak Stability

The feeling of stability comes from the righting moment that the kayak exhibits when it's in a heeled position.  The higher the righting moment, the more stable the kayak will feel.  The righting moment tends to be higher for lighter paddlers, and that is partly due to the lower CG as Laszlo mentioned.  There is an excellent discussion of kayak stability at http://www.guillemot-kayaks.com/guillemot/KayakStability

This graph shows the righting moment for different angles of heel, and you can see that the lighter paddler has the advantage with respect to stability.  You can download my design program if you want to play around with how changes in hull shape and paddler weight impacts the stability curves.  You can get it from this page: http://blueheronkayaks.com/kayak/software/software.htm


Stability Curves

RE: Kayak Stability

When an otherwise stable kayak seems unstable...it is the paddler.

You have to relax and flex at the waist, maintain a center of balance, using the paddle, no matter what the conditions are throwing at you. Hence the real reason you were ok and your friend was not ok in identical kayak's in the same conditions at the same time.


RE: Kayak Stability

Your friend might be a bit big for that boat. I am the same height and a little lighter than him.  When discussing my needs with John one time at a demo, he steered me away from the C-16 to a C-17. He indicated that for my size and weight, the 16 would be very tender.


RE: Kayak Stability

perhaps a more important question is what does your friend usually paddle is it more stable? jumping in a different boat takes a little getting used to also getting everything[foot pegs , back band seat position ]adjusted just right takes some time also most factory made boats have a soft chine while s&g boats are hard chined  when tipping they reach the point of n oreturn aka splash a bit more suddenly

RE: Kayak Stability

I am relatively new to kayaking. I paddle a C16 and have not yet rolled over.  It feels safe and stable even in a fair swell.  My question is am I paddling in a fools paradise unaware of impending  roll over or does one sense instability before this occurs?



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