Subject: Re: [baidarka] Tandem Dimensions
From: wolfgang brinck (nativewater@yahoo.com)
Date: Thu Feb 19 2004 - 12:18:45 EST
--- Harvey Golden <harveydgolden@yahoo.com> wrote:
The bifurcated bow and
> the truncated stern are in my opinion mostly quaint
> aesthetic touches on any kayak that isn't made to be
> flexible. When you see the bow of your baidarka 'hop'
> over a small wave before you even feel it in the
> cockpit-- you know it is working. A stiff-keeled
> kayak would not 'hop' so readily if at all; it simply
> has so much more weight to lift. The general feel of
> a 'loose' baidarka in seas is a very fluid sensation.
I generally agree with your analysis but the segmented keelson
continues to baffle me even though I have used it on all my baidarkas
in the past, trusting the wisdom of the original builders.
The problem is that if you take a long piece of wood and divide it up
into three segments, each segment by itself is stiffer than if they
were part of a larger piece of wood. Now if the three segments were
loosely jointed together, most of the flexing of the three part
system would be concentrated at the joints with little movement
elsewhere. But the joints on traditional boats aren't loose. They
are rather tightly bound. In the up and down direction the keelson
behaves pretty much as one piece. Where it does have some freedom of
motion is in the horizontal plane.
Another aspect of the keelson is that it provides only part of the
total longitudinal stiffness of the baidarka. Any tendency of the
keelson to flex at the joints will be counteracted by the ribs
gunwales and stringers.
There is one other possible use for the three part keel, and that is
that it might allow some stretch of the keelson. When the kayak is in
the trough of a wave, the two ends of the baidarka are pushed up. If
the keelson has no stretch, then it will tend to flatten out the ribs
or as John Heath had suggested, it will want to lay over on its side.
However, a three part keelson will have some ability to stretch
within the limits of the lashing material and may thereby avoid rib
flattening.
The baidarka frame at UC Berkeley uses heavy string wrapped around
the keelson joints but uses what looks like baleen to pull the keel
sections on either side of the joint toward each other. I don't know
if the baleen is at all elastic or if it was simply used for its
strength.
Finally, on the question of bones in joints, if I remember correctly,
the keelson segments had a kind of ball and socket arrangement built
into them with the balls being kind of almond shaped. Not sure
whether they would either encourage or discourage stretching of the
keelson or simply protect the wood from abrasion.
Wolfgang
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