Re: [Paddlewise] "Regular" paddle stroke

From: "Gabriel L Romeu" <romeug_at_erols.com>


> Steve Cramer wrote:
> > 
> > On Sat, 16 Jun 2001, Gabriel L Romeu wrote:
> > 
> > > Steve Cramer wrote:
> > > > Michael makes an excellent point about the blindness of the kayak. It
> > > > doesn't know where the paddle is, it just reacts to the forces exerted
> > > > by your butt, knees, and feet.
> > >
> > > This is just speculation, but I think you would be correct if we were
> > > paddling a spherical object in the water.
> > 
> > I'm not sure I can see the sequitur. A spherical kayak is blind to what
> > the paddle is doing, but our long skinny ones are not? 
>
> I agree with you Steve, but the effect of the stroke throughout the
> sweep  may not be uniform on the motion of the kayak.  
> 

Just a note.  The forces and moments in a sweep are mutually orthogonal.
That is, they are independent and their effects are independent.  The moments
cause turning.  The forces cause translation (linear motion).   These forces
and moments act through the paddler at the center of the kayak, not where
the blade touches the water.

My point made way back when was that the turning effects are not dependent 
on the location of the paddle blade (give or take biomechanical effects).  Niels 
brought to our attention the importance of the translation to certain paddlers, 
such as slalom kayakers.  He also pointed out that the linear forces when the 
paddle blade is drawn toward the kayak at the rear can contribute to the kayak's
stern yawing in a skid.

I think, in the end, that several different correct points have been made.  As you 
say, the motion is not uniform, even if the turning is.  In a full sweep, the lateral 
translations can cancel out, while the longitudinal translation results in a net
forward motion.  That's why you need alternate forward and reverse sweeps on
opposite sides of the kayak to do a 360 in a tight spot (cancel the longitudinal
motions).

As long as paddlers can keep these concepts straight, I'm happy.  If they don't and
start coming to ridiculous conclusions, I get cranky.  That's because I'm one of those
fastidious engineer types.

Mike


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