Re: [Paddlewise] Secondary stability... another way to think about it

Nick wrote:

(SNIP)

> I am also seeking a definition that does not depend on the paddler's
> skills. With practice, a skilled paddler can keep just about anything
> upright. A novice paddler may have trouble keeping a bath tub
> upright. Stability curves are determined assuming a rigid hunk of
> meat in the cockpit. This has the advantage of being skill
> independent, any idiot can by a rigid hunk of meat.
>
> My suggestion of looking at the inflection point is an attempt to
> quantify the feel in some boats that they get harder to lean at some
> point. Maybe this feeling should be called something else: "reserve"
> stability or something.

What about the rate at which stability changes. It seems that a boat that
has a rapid change of stability would fit what some paddler's call "notchy".
What could you add to the inflection point location information  that would
reveal this?

I think the slope in combination with the area under the curve has the
potential to tell us this. Finding some kind of "number" might prove
difficult, however.  I recall that the U.S. Navy has a method by which they
determine "safe" stability at high (above initial stability) heels. I don't
know how that will apply but maybe in some modified form it will.

One thought. Suppose you normalize the stability curve (i.e. make it non
dimensional by dividing the righting moment at every heel by the maximum)
and then compare the curves. It would seem that the boat with the greater
area under the curve beyond  the initial stability realm would feel like it
had the highest stability. One could easily check this if you had access to
a lot of paddlers and differing boats. In this way you might see relative
rather than absolute values and paddlers seem to like "relative".

John Winters
Waveform Plastics Technologies Ltd.
15 Ena Ave.
South River, Ontario
P0A 1X0



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