[Paddlewise] Stability

Nick wrote;

>  Primary stability has almost nothing to do with the cross sectional
> shape of a boat. Chines, no chines, makes no difference. It is the
> shape of the water plane and the height of the center of gravity that
> will determine initial stability.

Hmmm. Out of curiosity I drew two boats with the same displacement, same CG 
and same waterline area and shape. One had a "V" bottom and one a flat 
bottom. The flat bottom boat had a righting arm at 5 degrees 38% greater 
than the "V" bottom boat. That seems like a lot of effect. Granted this is 
an extreme example.

Maybe what Nick means is that, given two similarly shaped boats,  having a 
chine or no chine does not produce a significant difference. Am I reading 
you wrong on this, Nick?


Robert Livingston wrote;


> The fact is that secondary stability does not have a universally agreed 
> upon
> definition.

Certainly not among paddlers -  possibly because so much of the boat's 
stability depends upon the paddler and her skills. It seems to me that one's 
individual perception of stability  has a lot to do with the shape of the 
static stability curve and the range of stability (the range of inclination 
through which the boat is statically stable with a fixed CG).

Slow, creaky people like me seem to prefer a wide range of stability and a 
stability curve that has a slow rate of change throughout the range because 
we can't shift our weight so well anymore. Athletic types seem to get along 
fine with boats that have less static stability at all angles of heel, a 
smaller range and more rapid changes in stability with heel (as revealed by 
the slope of the stability curve) .

> We have stability curves for hundreds of kayaks. I have seen many of them.
> Secondary stability can not be identified as something on those curves or 
> at
> least there is no agreement on what that something is.

Once you have found a boat with a stability curve shape and magnitude that 
you like would not other boats with the same or similar curves "Feel" good 
to you? It seems to me that this suggests that the curve can tell you 
something.

 > So secondary stability is something mystical that cannot be "measured"
> objectively by a stability curve or anything else for that matter.
>
> Basically is  a subjective "impression" and thus cannot really be refuted.

If you can measure the stability and relate it to your preferences have you 
not accomplished something useful and possibly important? In short, the 
quantities may have no menaing to some one else but they would have meaning 
to the paddler.

I agree that to say a boat has "good" secondary stability is rather 
meaningless but to say I "like" (or don't like) the secondary stability of a 
boat has a lot of meaning.

Cheers

John Winters
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