Re: [Paddlewise] How a Kayak Turns (was: Mind Experiments ...)

From: Dave Kruger <kdruger_at_pacifier.com>
Date: Mon, 22 Jan 2007 13:10:24 -0800
Craig Jungers wrote:

> The mechanics of edging a kayak to make it turn faster are simple: basically
> you convert the hull from an essentially flat surface with little rise from
> end to end into a curved surface with rocker. The more you edge the more
> rocker you get and the faster the boat will respond to the turning moment
> imparted by your paddle blade. 

That's part of it; the other turn-inducing feature is that the hull is now 
asymmetric:  the "down" edge is curved in the direction of the turn; the 
"up" edge is curved in the direction opposite the turn (really, it is a 
portion of the hull you have rolled upward a bit) but has much _less_ 
curvature.  This difference, side-to-side, generates a turning force, also, 
which aids the paddle.  You can see how much this amounts to by starting a 
turn, edged, and then coasting, with no more paddling.  The boat should 
keep on turning, albeit not as tightly as when you were sweeping to help out.

> But there are situations in which you might want to do exactly the opposite.

> Another situation is when you are on the face of a wave surfing down and
> want to turn back up the wave and off the face. You'd edge towards the
> direction of the turn (and into the wave-face) while using your paddle to
> rudder your stern around. This would probably be really interesting in a
> round-bottomed sea kayak and your "edge" might turn out to be more of a
> side-slip. Remember that the water particles are move in a circular pattern:
> up the back of a wave and down the face of a wave so that you would not just
> be fighting gravity as you move across that wave-face.

Aren't the water particles moving _up_ on the _face_ of the wave and down 
on the backside?  If they were moving down on the face of the wave, 
wouldn't the water level on the face be falling instead of rising?

> Skiers talk about "carving" turns as they move down the face of the slope
> and so do white-water kayakers.

And edging on skis with heavy sidecut is an entirely different game than 
edging a kayak (WW or other wise) because sidecut generates a curved edge 
that interacts with the surface to generate turning forces _toward_ that 
side, not away from it.  [I feel particularly unqualified to discuss the 
mechanics of sidecut on snow, inasmuch as I never learned to do parallel 
turns!  Strictly a skidded turn guy, perhaps a consequence of my surfer 
heritage and upbringing!]

-- 
Dave Kruger
Astoria, OR
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Received on Mon Jan 22 2007 - 13:11:13 PST

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