Re: [Paddlewise] lift and efficiency

I think it is a bit misleading to think of turbulence as merely an
indication of inefficiency. Any motion in the water is the _reaction_ from
the _action_ of moving your boat forward and as such is both a sign of
power being applied and an indication of inefficiency. Even if your paddle
is working completely with laminar flow it is still moving the water. The
energy lost to moving water does not discriminate between smooth and
chaotic motion. If you move (m) grams of water at a velocity (v) the energy
involved in moving it is the same. (Have I said the same thing enough times
yet?) The inefficiency is also not indicated by slippage (distance between
entry and exit), but how much water is moved, and more importantly, how
fast. How that water is moved is not important.

It is important what direction the water is initially moved. Note that if
you were able to place a paddle so the only motion through the water was
parallel to the direction of motion (pure drag), all the force applied to
it would be used for propelling the boat. As soon as you start moving the
paddle off parallel, you introduce a component of drag perpendicular to
your motion. This is wasted effort. This is not to imply that good things
can not be obtained from that off-parallel motion, but you are introducing
another source of inefficiency to your analysis. BTW once the water has
moved beyond the influence of the paddle it can move anywhere it wants
without effecting efficiency.
 Nick


At 12:30 AM -0700 7/27/98, K. Whilden wrote:

>Ok, now lets talk about lift... but first lets talk about drag. The
>paddler is pulling backwards on the paddle (force vector points towards
>the stern). The resistance of the water (drag) on the paddle resists that
>pull (force vector points towards the bow). The drag force vector is
>slightly smaller than the paddler force vector, which is another way to
>think about efficiency. The difference in the size of the vectors
>represents the energy that is lost due to turbulence and the slippage of
>the paddle through the water. When lift is generated due to laminar flow,
>the size of the resistance vector is slightly increased because the lift
>vector points in the same direction as the drag vector. Even if further
>calculations were to show that the lift generated by Greenland paddles
>really is insignificant, efficiency is probably still increased because
>there is a lot less turbulence created by the laminar flow. And note,
>modern, non-wing paddles can significantly reduce turbulence by slicing
>the paddle outwards away from the kayak, just like racers and greenland
>paddlers.
>
>Well, the concepts above are quite clear to me, but I wonder how clear it
>is to the readers. I suppose I could put it down on a web page, with force
>vector diagrams, and with maybe even a bonus picture of me waving my
>hands.  Anyhow, I hope my definitions make sense, and maybe clear up a
>little confusion.
>
>Cheers,
>Kevin
>	 ___________________
>
>	/   Kevin Whilden   \
>       |Dept. of Geosciences \___
>       |University of Washington \
>       |kwhilden_at_u.washington.edu|
>        \________________________/
>
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Nick Schade
Guillemot Kayaks
c/o Newfound Woodworks, 67 Danforth Brook Rd, Bristol, NH 03222
(603) 744-6872

Schade_at_guillemot-kayaks.com
http://www.guillemot-kayaks.com/

>>>>"It's not just Art, It's a Craft!"<<<<


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