Re: [Paddlewise] Stability

> How true. If one states that shape has no effect then it must have no
> effect. If it can bge shwn that it does have an effect then you have a
> different ball game and need to restate the theory. Maybe to, " Of the
> factors affecting initia stability CG and beam have the greatest effect and
> waterplane area and underwater shape have lesser effects.


As I understand stability curves, PRIMARY stability is almost entirely a
function of the waterplane (one of which parameters is its width) assuming
the center of gravity above the water surface is held constant.

The other factor is perhaps the flare of the sides of the kayak at the
waterline. If there is a substantial angle, it makes a difference in the
calculation of primary stability. (Basically the equations compare the
waterplane at 0 degrees of tilt with the waterplane at very small delta
degrees of tilt.)

Most commercial boats (when loaded) have fairly vertical sides at the
waterline. So the calculations would have to be for a loaded boat to prove
my point. 

Some 30lb boat with a V bottom might have a substantial angle at the
waterline if it was unloaded (just perched on the water) but the commercial
boats that I see do not have much angle at the waterline when loaded. I
could design a cross-section that had a major flare right at the loaded
waterline but I do not see such boats "out there". Any major flare tends to
greatly increase the seam width.

I would say that the cross-section that is under the water and stays
underwater when the boat is heeled a fraction of a degree has no effect on
the PRIMARY stability. The equations do not "care" whether that is a square
shape or a round shape or a V shape or some bizarre shape. I thought that
was Nick's message and I would agree with him.

So I would continue to maintain that the underwater shape (that stays
underwater as the kayak heels a fraction of a degree) has no influence on
the primary stability. It just does not show up in the equations.

(But, to reiterate, I think that it can have an influence on initial
stability as perceived by the paddler -- roll resistance or whatever you
want to call it.)
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