Re: [Paddlewise] Stability

> Sea Kayaker placed the center of gravity of
> 150 pounds (representing the paddler) 10" above the seat bottom when
> measuring a kayaks stability (with a torque wrench). Perhaps the seat height
> was higher in the Chinook (Sea Kayaker didn't publish the seats height at
> that time). 


That is the problem with that early Sea Kayaker data. My challenge applies
to a case where the center of gravity above the bottom of the boat (or the
waterline if preferred) is the SAME.

If you measure from the top of the seat, then, of course, all bets are off
as it depends on the height of the seat. It turns out that very slight
changes in the height of the center of gravity make a big difference in the
curves. As Winters points out, this has to be held constant.*

I will stick with my contention that the width is paramount if the height of
the center of gravity is the same for the kayaks being compared.

Counter-examples where the height of the center of gravity is different or
"unknown" do not count.  :)


>Imagine a hollow diamond shaped water plane
>compared with a full rounded shape of the same length and width. Since
>longer length also increases the water plane, longer length increases the
>static stability of the kayak if width and other factors are held constant.

I agree that the water plane makes a difference. The hollow diamond shape
will be less stable for a given width. My contention is that the width is
more important. An inch of extra width will trump the water plane every
time.

I would concede to Matt that the length of the boat is going to make a
difference and I sort of glossed over this. Long boats, for a given width,
will tend to be more stable. If you are going to try and find a commercial
design that is an exception to the rule that wider (by 1 inch) is always
more stable it would be comparing a hollow diamond very short kayak with a
"full" shaped very long kayak. It would require a dramatic difference in
length however to sway the numbers.

___________________________________________________________

* Even now that Sea Kayak publishes the height of the seat, I have never
"liked" the approach of measuring from the height of the seat because
designers who put higher seats in are going to be "punished" in the sense of
having their boats look less stable. Another kayak with a very low seat will
look more stable although the seat may be so low that everyone who actually
buys that boat ends up installing a nice thick foam cushion to raise
themselves up a bit.
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