Subject: Re: baidarka stability...
From: Douglas Ingram (redcanoe@pangea.ca)
Date: Tue Dec 12 2000 - 15:27:58 EST
Peter wrote:
"> 1. The term secondary stability is unique to the kayaking community, it
> appears in no other navel architecture or watercraft usage"
and I add:
Except canoes!
> speculate this is because only in a kayak does it have relevance since you
> control the kayak with weight shift and body movements, this allows the
> "captain" to control the craft (which really becomes an extension of
> his/her body) through rough conditions in a way not possible with other
> water craft.
>
> 2. It has no precise definition and therefore really can not be measured
> or rated other than subjective feel of the kayaker. Some have tried to
> show correlation with the stability curves though others pointed out (me
> included) there was no consistent measurable quantity that can be
> determined from the curves. In other words, by looking at the curves
alone
> you could not say which kayak would have good secondary stability and
which
> would not, it is too subjective.
>
> I personally think a measure could be developed but it would take a lot of
> different kayaks, a lot of different paddlers, and a lot of testing and
> cross correlation between different measurable qualities, not just the
> quasi-static righting moment curves you see in SK magazine.
>
> I suspect however that the higher heel or roll angle that one feels secure
> or comfortable with in a kayak, the more most people would identify as
> having good secondary stability. The perception of the angle of heel is
> the important issue, if you can roll a kayak on it's edge and comfortably
> hold it there, it feels like it has good secondary stability. OTOH, even
> if a kayak is rock steady at low angles of heel but you find you can not
> hold it on it's edge, most would say it has high initial stability and low
> secondary stability.
>
> There are similar terms used in Naval Architecture called initial and
> overall stability, which do have definitions but are not quite the same
> thing. Most text books define initial stability at heel angles less than
> 10 degrees, and overall stability as the maximum righting moment achieved
> by the hull design beyond this 10 degrees. Of course in just about
> everyother water craft, and certainly virtually all commercial vessels,
you
> can not apply a righting force as you can with weight shift and bracing in
> a kayak. So the term overall stability likely has another meaning in the
> mind of a hull designer I would guess, than secondary stability does to a
> kayaker.
>
>
> Peter
>
>
>
>
>
>
> On Monday, December 11, 2000 7:06 AM, Chuck
> [SMTP:Sparky@thewizardworks.com] wrote:
> > Hello all...
> >
> > I'm a bit confused as to the differences between initial and secondary
> > stability. Might someone clear this up for me?
> >
> > Thanks!
> >
> > Chuck
> >
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