Re: [Paddlewise] stability of folding vs. hardshells

Leander wrote:
> 
> At 11:44 AM 09-04-99 -0700, Philip Torrens wrote:
> >
> >Okay, I can't express this in formal technical terms, but I think Ralph
> may be
> right (upright?) in feeling that a sponsoned folding boat could be more stable
> and self-righting than a hardshell of equal chine and beam. (I mostly use hard
> shells so I'm not biased in favour of folding boats.)
> >The displacement of a hardshell is essentially static, changing only as the
> entire boat moves. The sponsons of a folder, in contrast, are squeezed at the
> bottom as they are pushed deeper into the water, and therefore expand into
> greater width and stability in the higher parts.  ...snipped...
> 
> I long ago read an article on this very subject, complete with formulas,
> but it
> basically said what you so eloquently and succinctly described. Though the
> reference is long since lost, perhaps the design experts on the list, such as
> John or Nick, know of it.

Philip's and Leander's comments remind me of something interesting about
the way a sponsoned folding kayak behaves when it has taken on a lot of
water.  If you turn that folding kayak on its side, it will rise on the
sponson on that side and spill a lot of the water out, up to about the
inside level of the sponson.  (It is a neat way to begin partial
emptying of a folding kayak that most people don't know about.  The
phenomenon is even more pronounced if you also have flotation bags fore
and aft as you alway should in any folding kayak or non-bulheaded
kayak.)

If there were no different in the displacement effect between a
hardshell and a folding kayak with sponsons, then this float-up
phenomenon would also happen with a hardshell laid on its side.  To my
knowledge, the hardshell would not at all rise that way to spill out the
water, only the sponsoned kayak would.  That column of compressed air in
the sponson is fighting its way to the surface.  In a corollary way, it
also resists being submerged.  Philip's idea of a dynamic as opposed to
static displacement certainly has a ring to it that shows itself in real
life.

There are so many ways of skinning a cat in the kayaking world.  Some
corners of this realm offer some unique advantages that some people
don't seem to want to hear about or want to put outside the kingdom's
gate as not worthy.  For example, the earlier sit-on-top kayak
discussion that I engendered that drew some flak.   But let's face it,
there ain't nothing easier to empty than an SOT nor much easier to get
back into without pumps, paddle floats, re-enter and roll and all that. 
Also the middle range of SOTs are every bit as fast as the middle range
of beamier hardshells made of polyethylene and are considerably stable. 
Performance kayaks require performance paddlers and a lot of people
getting into kayaking are simply not going to work at getting and
keeping the skills.  Wouldn't these paddlers be better off with kayaks
that are less skill reliant?

ralph diaz  
-- 
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Ralph Diaz . . . Folding Kayaker newsletter
PO Box 0754, New York, NY 10024
Tel: 212-724-5069; E-mail: rdiaz_at_ix.netcom.com
"Where's your sea kayak?"----"It's in the bag."
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